For a generalized radiation problem,an infinitely long submerged horizontal cylinder is forced to vibrate periodically in the transverse direction,with a described elastic harmonic motion along its longitudinal direct...For a generalized radiation problem,an infinitely long submerged horizontal cylinder is forced to vibrate periodically in the transverse direction,with a described elastic harmonic motion along its longitudinal direction.A critical frequency corresponds to the described wave number of elastic vibration,and the generalized hydrodynamic coefficients abruptly change in the vicinity of critical frequency.In this work,a numerical examination is carried out to study the characteristics of wave profiles and wave propagation in the vicinity of the critical frequency.Results show that below the critical frequency,the real parts of complex wave profiles have large values in the vicinity of the cylinder and decay to zero with the increasing distance from the cylinder.Meanwhile,the imaginary parts of complex wave profiles are all zero,which explains why the generalized radiation damping is zero when the vibration is less than the critical frequency.At far distances,no radiation wave is observed.When the vibration exceeds the critical frequency,the real and imaginary parts of the wave profiles oscillate harmonically and keep steady amplitudes.In addition,the generated radiation wave propagates obliquely outward.The influence of the cylinder’s submergence depth on the wave profile is also studied,and the results indicate that the amplitude of the wave profile decreases as the submergence depth of the cylinder increases.The 3D wave profiles are graphically presented to show the wave propagation characteristics in the vicinity of the critical frequency for this generalized radiation problem.This study provides a good reference for the interaction between fluid and slender elastic structures.展开更多
BACKGROUND Critical flicker frequency(CFF)is a quantitative tool for assessing hepatic enceph-alopathy(HE),particularly minimal HE,which is associated with poor prognosis in liver cirrhosis.Alcohol-related liver disea...BACKGROUND Critical flicker frequency(CFF)is a quantitative tool for assessing hepatic enceph-alopathy(HE),particularly minimal HE,which is associated with poor prognosis in liver cirrhosis.Alcohol-related liver disease(ALD)is a leading global cause of cirrhosis;however,the effects of alcohol on CFF and its relationship with liver stiffness(LS)remain underexplored.AIM To study the impact of alcohol withdrawal on CFF and its correlation with LS in ALD patients.METHODS A total of 108 patients were included:93 heavy drinkers hospitalized for detoxi-fication,15 with non-ALD etiologies,and 20 healthy controls.CFF was measured using the Hepatonorm analyzer,and LS via transient elastography(FibroScan).Baseline and post-detoxification assessments were conducted in 57 ALD patients.RESULTS The cohort had a mean age of 53.7±13.8 years,with 74% male participants.CFF measurements were reliable,with 97.2% of patients showing an interquartile range<20%.ALD patients exhibited significantly lower CFF compared to controls.Receiver operating characteristic analysis for overt HE(n=12)yielded an area under the curve of 0.66(95%confidence interval:0.49-0.84,P=0.0142),with an optimal cutoff of 36.5 Hz.CFF significantly improved post-detoxification.Patients with LS>17 kPa had lower CFF,while those with intermediate LS showed no significant difference.CONCLUSION CFF is influenced by HE severity and acute alcohol exposure,showing improvement after detoxification.Its weak correlation with fibrosis stage suggests that CFF serves as a sensitive neurocognitive marker in ALD.展开更多
Rollover of commercial heavy vehicles can cause enormous economic losses and fatalities.It is easier for such vehicles to rollover if the driver’s steering frequency is close to the critical frequency of the vehicle...Rollover of commercial heavy vehicles can cause enormous economic losses and fatalities.It is easier for such vehicles to rollover if the driver’s steering frequency is close to the critical frequency of the vehicle’s roll motion;however,the critical roll frequency has rarely been investigated.In this study,the second-order transfer function between the steering input and roll angle was developed to calculate the critical frequency of the vehicle’s roll motion.The simulated spectrum and transfer function were then used to dynamically predict the peak lateral load transfer ratio.Laboratory experiments were conducted using a scaled vehicle to verify the critical roll frequency.The results suggest that the peak value of the lateral load transfer ratio during steering can be accurately determined from the driver’s input,and the critical roll frequency has a dominant effect on the dynamic rollover of heavy vehicles.展开更多
A model for the negative phase of ionospheric storms in middle latitudes is presented. It is assumed that there will be molecule enriched air in the thermosphere above the auroral oval during the period of the main ph...A model for the negative phase of ionospheric storms in middle latitudes is presented. It is assumed that there will be molecule enriched air in the thermosphere above the auroral oval during the period of the main phase of a magnetic storm. The molecule enriched air is carried to the middle latitudes by thermospheric neutral wind, and at the same time it diffuses away. When the molecule enriched air arrives at the F2 layer above a station, the electron loss rate in the F2 layer increases, the electron density decreases and then the negative phase at the station begins. We have calculated the variations of the fo F2 following magnetic storms for Manzhouli （29.5°N, 117.5°E）, Freiburg （48°N, 07°E） and Billerica （43°N, 71°W） respectively. The results agree very well with typical events observed at the three stations and can be used to explain some average features of negative phase ionospheric storms in middle latitudes.展开更多
BACKGROUND:Minimal hepatic encephalopathy (MHE) impairs quality of life and predicts overt hepatic encephalopathy (HE) in cirrhotic patients.Diagnosis of MHE requires cumbersome tests.Lactulose is effective in the tre...BACKGROUND:Minimal hepatic encephalopathy (MHE) impairs quality of life and predicts overt hepatic encephalopathy (HE) in cirrhotic patients.Diagnosis of MHE requires cumbersome tests.Lactulose is effective in the treatment of MHE.This study aimed to evaluate the use of critical flicker frequency (CFF) for the diagnosis of MHE in cirrhotic patients after treatment.METHODS:One hundred and ten patients were evaluated by psychometry (number connection tests A,B or figure connection tests A,B),P300 auditory event related potential (P300ERP),venous ammonia,and CFF for MHE.MHE was diagnosed by abnormal psychometry (>2SD age matched controls) and P300ERP.MHE patients were treated with lactulose for one month.Response was defined by normalization (<2SD of matched controls) of both psychometry and P300ERP.RESULTS:Of the 110 patients [Child Turcott Pugh score A:B:C 39:42:29,(age 41.6±11.6 years,M:F 82:28)],75 (68%) had abnormal results of psychometric tests,and 74 (67%) had prolonged P300ERP.Fifteen (20%) patients with abnormal results of psychometric tests had normal P300ERP.Thus sixty (54.5%) patients were diagnosed as having MHE.After treatment for one month,34 (57%) recovered while 26 (43%) continued to have abnormal resents of psychometric or P300ERP tests.CFF was <39 Hz in 72 (65.4%) patients before treatment and in 20 (33.3%) after treatment.CFF sensitivity,specificity,positive predictive value,negative predictive value,and diagnostic accuracy for the assessment of recovery of MHE were 65%,91%,85%,77% and 80%,respectively.CONCLUSION:CFF is a simple,relatively reliable,and accurate test without any dependence on age or literacy in the diagnosis and assessment of recovery of patients with MHE.展开更多
With an increase in the density of the seed roll in the roll box of the saw gin, the quality indicators of the fiber and seed are poor, energy consumption increases, machine breakdowns increase, and when the density d...With an increase in the density of the seed roll in the roll box of the saw gin, the quality indicators of the fiber and seed are poor, energy consumption increases, machine breakdowns increase, and when the density decreases, the performance of the saw gin increases. Therefore, the density control of the seed roll is one of the important problems in the ginning process. The paper proposes a change in the rotation speed of the saw cylinder with a decrease in the diameter of its numerical linear speed and machine productivity. The article describes the problem of regulating the density of a seed roll in a saw gin of the DP series, provides an overview of work on regulating the operation of the machine, determines the dependence of the productivity of gins and linters on the state of the saw system in these machines, as well as changes in the linear speed of the saw by changing its diameter. Also, the critical speed of the gin and linter saw cylinder was determined to prevent resonance. In this case, the Simulation package of the SolidWorks computer program was used. The results of the study made it possible to adjust the speed of the cylinders when changing the diameter of the saws, which improved the productivity of the machine while maintaining the quality of the fiber and seed.展开更多
The effects of the location,number and stiffness of guide pads on the lowest critical rotational frequencies of the rotating circular saw damped at the inside and free at the perimeter are discussed by the non linear...The effects of the location,number and stiffness of guide pads on the lowest critical rotational frequencies of the rotating circular saw damped at the inside and free at the perimeter are discussed by the non linear theory and the perturbation theory of structural vibration analysis The influence of the centrifugal force and the cutting temperature are considered in the course of the analysis The results of the analysis and the calculation show that the introduction of one guide does not stably raise critical rotational frequencies of the circular saw The two guides can raise lowest critical rotational frequency of the circular saw when the angle between the two guides fixed on the direction of the circumference satisfies the certain conditions展开更多
A theoretical model of describing the electromagnetic and thermal dynamics of high-Tc superconducting bulks in a high-Tc superconducting Maglev system is built up.The model contains the effects of hysteresis-type loss...A theoretical model of describing the electromagnetic and thermal dynamics of high-Tc superconducting bulks in a high-Tc superconducting Maglev system is built up.The model contains the effects of hysteresis-type loss,flux flow,flux creep,and thermal diffusion on the superconducting bulks in the Maglev system.As the first stage of this study,the behavior of magnetic and electric fields,as well as the distribution energy flow density in the superconducting bulk is studied.The results show that the flux flow and thermal diffusion affect the behaviors of the electromagnetic field in the high-Tc superconducting bulks in different ways;however,both of them contribute significantly to the energy dissipation of the superconducting bulks when they are used in the Maglev train.展开更多
Despite the continuous improvement of the widely used empirical model international reference ionosphere(IRI),the recently appeared new models must be tested worldwide.Testing along the meridians has the advantage of ...Despite the continuous improvement of the widely used empirical model international reference ionosphere(IRI),the recently appeared new models must be tested worldwide.Testing along the meridians has the advantage of dealing with the latitudinal dependent parameters.This paper uses new models of parameters foF2(critical frequency),TEC(total electron content),andτ(equivalent slab thickness of the ionosphere),which are of great importance for evaluating the effects of space weather.IRI-Plas,NNT2F2,and NTSM models were tested using data from 6 ionosondes located along the meridian 110°E in March 2012.It is shown that the IRI-Plas model provides the closest values to experiment with respect toτ,while the NTSM model provides a rather limited reflection of the latitude dependence.Analyses of foF2(NNT2F2)have shown that,the NNT2F2 model provides good conformity with experimental values in this area,but it is very dependent on the TEC processing method.The latitudinal dependences of foF2 obtained with TEC and polynomial dependenceτ(Appr)showed the presence of positive deviations from medians not only during disturbances but also quiet periods,longitudinally at the meridian.展开更多
In this paper, we use an empirical method to derive the height of maximum electron concentration of the F2 region and the effective meridional neutral wind at Great Wall Station, Antarctica. The meridional wind is als...In this paper, we use an empirical method to derive the height of maximum electron concentration of the F2 region and the effective meridional neutral wind at Great Wall Station, Antarctica. The meridional wind is also calculated with the HWM90 model. Results can be used to explain two anomaly features of ionosphere at Great Wall Station. In summer, peak values of f0F2 appear during nighttime. In winter, especially during June and July, f0F2 decrease dramatically as compared with summer's one.Summer anomaly can be explained by combining effects of two causes:thermospheric winds and solar radiation. An important reason for the anomaly is the location of Great Wall Station, which is in both high geographic latitude and middle geomagnetic latitude.展开更多
AIM: To evaluate the association between serum concentrations of S100β in patients with cirrhosis and the presence of low grade hepatic encephalopathy (HE).METHODS: This was a cross-sectional study. The po...AIM: To evaluate the association between serum concentrations of S100β in patients with cirrhosis and the presence of low grade hepatic encephalopathy (HE).METHODS: This was a cross-sectional study. The population was categorized into four groups healthy subjects, cirrhosis without HE, cirrhosis with covert hepatic encephalopathy (CHE) and cirrhosis with overt HE. Kruskal-Wallis, Mann Whitney’s U with Bonferroni adjustment Spearman correlations and area under the ROC were used as appropriate.RESULTS: A total of 61 subjects were included, 46 cirrhotic patients and 15 healthy volunteers. S100β values were different among all groups, and differences remained significant between groups 1 and 2 (P < 0.001), and also between groups 2 and 3 (P = 0.016), but not between groups 3 and 4. In cirrhotic patients with HE S100β was higher than in patients without HE [0.18 (0.14-0.28) ng/mL vs 0.11 (0.06-0.14) ng/mL, P < 0.001]. There was a close correlation between serum concentrations of S100β and psychometric hepatic encephalopathy score in patients with cirrhosis without HE compared to the patients with cirrhosis with CHE (r = -0.413, P = 0.019). ROC curve analysis yielded > 0.13 ng/mL as the best cutoff value of S100β for the diagnosis of HE (sensitivity 83.3%, specificity 63.6%).CONCLUSION: Serum concentrations of S100β are higher in patients with cirrhosis than in healthy volunteers, and are further increased in the presence of hepatic encephalopathy. The results suggest that serum biomarkers such as S100β could help in the correct characterization of incipient stages of HE.展开更多
Background:Due to media opacity,it is usually difficult to accurately evaluate the postoperative visual acuity in cataracts patients.As a small and portable tool,the critical flicker fusion frequency(CFF)device reflec...Background:Due to media opacity,it is usually difficult to accurately evaluate the postoperative visual acuity in cataracts patients.As a small and portable tool,the critical flicker fusion frequency(CFF)device reflects the temporal resolution of visual function and has been widely used in clinical research.However,poor understanding of the technique and equipment limitations have restricted its clinical application in China.Main text:There was a decrease in the CFF value in various ophthalmic diseases,indicating that the CFF is sensitive to detect visual functional changes.A number of studies have shown that the CFF test can accurately distinguish patients with simple cataracts from those with cataracts combined with fundus disease,and,as a visual test,it can more accurately predict postoperative visual acuity without being affected by media opacity.This study comprehensive reviews the basic principles of CFF and its application in ophthalmology,especially in cataracts.Conclusions:As one of the tools for dynamic visual function detection,the CFF test could help doctors to assess the possible presence of fundus disease in cataracts patients,especially in eyes with dense cataracts,and more precisely provide a reasonable visual prognosis than other available visual tests.展开更多
Delaminations in structures may significantly reduce the stiffness and strength of the structures and may affect their vibration characteristics. As structural components, beams have been used for various purposes, in...Delaminations in structures may significantly reduce the stiffness and strength of the structures and may affect their vibration characteristics. As structural components, beams have been used for various purposes, in many of which beams are often subjected to axial loads and static end moments. In the present study, an analytical solution is developed to study the coupled bending-torsion vibration of a homogeneous beam with a single delamination subjected to axial loads and static end moments. Euler-Bernoulli beam theory and the ＂free mode＂ assumption in delamination vibration are adopted. This is the first study of the influences of static end moments upon the effects of delaminations on natural frequencies, critical buckling loads and critical moments for lateral instability. The results show that the effects of delamination on reducing natural frequencies, critical buckling load and critical moment for lateral instability are aggravated by the presence of static end moment. In turn, the effects of static end moments on vibration and instability characteristics are affected by the presence of delamination. The analytical results of this study can serve as a benchmark for finite element method and other numerical solutions.展开更多
Minimal hepatic encephalopathy(MHE)is a critical neurocognitive complication of decompensated liver cirrhosis and portosystemic shunting,which results in a wide range of cognitive deficits including impairments in wor...Minimal hepatic encephalopathy(MHE)is a critical neurocognitive complication of decompensated liver cirrhosis and portosystemic shunting,which results in a wide range of cognitive deficits including impairments in working attention,psychomotor speed,and executive function.Current guidelines have recommended paper-and-pencil psychometric tests for the diagnosis of MHE.Most high-risk cirrhotic patients are required to be examined;however,paperand-pencil psychometric tests are neither convenient nor rapid to perform in the clinic.Recently,novel computerized psychometric tests,including the inhibitory control test,EncephalApp Stroop App,and critical flicker frequency,have been proven to be rapid,effective,and convenient methods for screening MHE in clinical practice and for identifying high-risk cirrhotic patients for further validation using rigid neuropsychometric examinations.However,diagnostic accuracy of these tests is influenced by educational background,age,and cultural differences.This review summarizes clinical evidence of the application of novel computerized psychometric tests for screening MHE.展开更多
The purpose of this study was to assess the effects of reducing driving fatigue with magnitopuncture stimuli on Dazhui (DU14) point and Neiguan (PC6) points using heart rate (HR), reaction time (RT) testing, critical ...The purpose of this study was to assess the effects of reducing driving fatigue with magnitopuncture stimuli on Dazhui (DU14) point and Neiguan (PC6) points using heart rate (HR), reaction time (RT) testing, critical flicker fusion frequency (CFF) and subjective evaluation. Twenty healthy subjects were randomly divided into two groups: A-group (study group) and B-group (control group). All subjects were required to be well rested before the experiment. The subjects were engaged in high speed driving at a constant vehicle velocity of 80 km/h continuously for three hours on a test course simulating an expressway. During the driving magnitopunctures were applied to the Dazhui (DU14) point and Neiguan (PC6) points for the A-group when the subject performed the task for two and half hours, and for the B-group magnitopunctures were applied to non-acupuncture points at the same time session. In this study RT exbited a significant delay in B-group (P<0.01) but no found in A-group after the driving task. CFF and subjective evaluation also exhibited significant differences between the two groups after the driving task (P<0.05). The findings showed that magnitopuncture stimuli on Dazhui (DU14) point and Neiguan (PC6) points could reduce the effects of driving fatigue.展开更多
Purpose:To investigate the application of critical flicker fusion frequency(CFF)in demyelinating optic neuritis(DON).Methods:A cross-sectional study.A total of 127 eyes in 69 DON patients and 63 eyes in 33 healthy con...Purpose:To investigate the application of critical flicker fusion frequency(CFF)in demyelinating optic neuritis(DON).Methods:A cross-sectional study.A total of 127 eyes in 69 DON patients and 63 eyes in 33 healthy control(HC)groups were included between January 2021 to September 2021 from Department of Ophthalmology,PLA General Hospital.Patients underwent best-corrected visual acuity(BCVA),visual field,optical coherence tomography(OCT),flash visual evoked potential(F-VEP),and CFF examinations.The affected eyes were divided into aquaporins 4(AQP4-),myelin oligodendrocyte glycoprotein(MOG-),and double negative DON according to serum antibody;mild,moderate,severe degree visual impairment according to BCVA0.5,0.1-0.5,<0.1;and 4 groups:<1,1~<3,3~<6 and>6 months according to time interval from onset to CFF examination.One-way ANOVA was used to perform above subgroup analysis.The correlations between CFF and F-VEP peak time,peak value,BCVA and mean visual filed defect(MD)were analyzed in order via Pearson correlation analysis.Results:he trichromatic values of red,green,and yellow in DON affected eyes were 21.83±9.03,23.66±10.21,24.09±10.77 Hz,respectively,which was significantly reduced compared with the HC group(t=-14.82,-14.22,-14.00;P<0.001).The subgroup analysis showed no significant difference between different antibody subtypes(P=0.914<0.848<0.604),whereas,a significant decrease of CFF trichromatic value was found in severe visual acuity impairment group(P<0.001).There was a significant difference in CFF-trichromatic values at different time points(P<0.001),to be specific,CFF fluctuated under 20Hz within 3 months after onset and tended to be stable around 24-28Hz.Correlation analysis showed that the peak time of F-VEP(r=-0.486,-0.515,-0.526;P<0.001),BVCA(r=-0.640,-0.659,-0.642;P<0.001),were negatively correlated with CFF trichromatic values,MD and CFF were positively correlated(r=0.486,0.453,0.476;P=0.003,0.006,0.004).Conclusions:A significant decrease of CFF value was found in DON-affected eyes,and it has a good correlation with BCVA,MD and latency of F-VEP,and can better reflect the impairment of visual function.展开更多
The vertical ionogram can provide the important ionospheric parameters, such as critical frequency, virtual height and electron density, for ionospheric research. The oblique ionosonde has the ability to detect the io...The vertical ionogram can provide the important ionospheric parameters, such as critical frequency, virtual height and electron density, for ionospheric research. The oblique ionosonde has the ability to detect the ionosphere over sea and other terrain where it is not practical to deploy vertical sounder and provide more ionograms with less transmitting and receiving devices. Therefore, the conversion of the oblique ionogram to vertical ionogram for obtaining the important ionospheric parameters is a very useful inversion technology. The experimental comparison between oblique and vertical detections was carried out in the equatorial ionospheric anomaly (EIA) region of south China on 25 and 26 August 2010. The oblique detecting path was from Wuhan to Shenzhen and the VI ionosonde was located in the midpoint of the oblique path. The oblique ionogram reversion results showed a small deviation of the critical frequency, minimum virtual height as well as the electron density profile of the ionospheric F layer, as compared with the real vertical observations.展开更多
The analysis of the satellite altimeter data suggests that the propagating speed of intraseasonal long Rossby wave amplified in the subtropical Pacific Ocean is faster than that of first mode baroclinic free Rossby wa...The analysis of the satellite altimeter data suggests that the propagating speed of intraseasonal long Rossby wave amplified in the subtropical Pacific Ocean is faster than that of first mode baroclinic free Rossby wave predicted by the liner theory and the propagating speed of intrascasonal long Rossby wave reflected in the eastern boundary of Pacific Ocean agrees basically with the liner theory speed of first mode baroelinic free P, ossby wave. If we do not distinguish the two kinds of hmg Rossby waves and estimate the Rossby wave speed in the whole basin, the phase speed is merely 25% higher than the linear theory long Rossby wave speed. The acceleration of the propagating speed of intraseasonal long Rossby wave amplified in the subtropical Pacific Ocean is due to the existence of westward thermolcline mean flow.展开更多
Nighttime enhancements in ionospheric electron density at mid- and low-latitudes are investigated by using the critical frequency of the F2-1ayer （foF2） data measured from ionosonde stations at Okinawa （26.3°N...Nighttime enhancements in ionospheric electron density at mid- and low-latitudes are investigated by using the critical frequency of the F2-1ayer （foF2） data measured from ionosonde stations at Okinawa （26.3°N, 127.8°E, Geomagnetic 15.3°N）, Yamagawa （31.2°N, 130.6°E, Geomagnetic 20.4°N）, Kokubunji （35.7°N, 139.5°E, Geomagnetic 25.5°N）, and Wakkanai （45.4°N, 141.7°E, Geomagnetic 35.4°N） in East Asia during several solar cycles. The results show that there are obvious seasonal and solar activity dependencies of the nighttime electron density enhancements. The enhancements are termed pre-midnight enhancement and post-midnight enhancement, according to the local time when the enhancement appeared. The former has a higher occurrence probability in summer months than in winter months. In contrast, the latter has a larger occurrence probability in winter months than in summer months. Moreover, the nighttime enhancements in electron density are more likely to occur at lower solar activity. These seasonal and solar activity variations of the nighttime enhancements in electron density can be explained in terms of the combined effects of downward plasma flux from the plasmasphere and the neutral winds.展开更多
The vibration of dusty surfaces inevitably causes re-entrainment of particles into the atmosphere.Given that movement of mineral dust particles deposited on a surface begins at a critical frequency (fc) and amplitude,...The vibration of dusty surfaces inevitably causes re-entrainment of particles into the atmosphere.Given that movement of mineral dust particles deposited on a surface begins at a critical frequency (fc) and amplitude,an experimental laboratory study was conducted to determine the onset conditions for resuspension of a vibrated granular soil.We determined the resuspension state diagram as a function of frequency and amplitude of a sinusoidal vibration,the granulometry of the dust and the thickness of the soil bed.The mitigation effect of humidity was also evaluated.Critical frequencies ranged between 2.5 and 23 Hz when amplitudes were less than 12 rmm.These results were independent of bed thickness and perturbation type.For all particle sizes observed,fc decreased monotonically with A,contrasting with behavior observed for individual particles.In dry samples,fe for large size classes was markedly less when A was greater than 6 mm;while thefc for fine fractions only decreased once amplitudes reached 10 mm.Experiments with wet granular soils demonstrated that wetting above an optimum humidity did not necessarily impede movement and caused agglomeration.This study provides guidelines for managing resuspension of granular soils subjected to vibrations.展开更多
基金supported by the National Key Research and Development Program of China(2022YFB2602800)National Natural Science Foundation of China(No.52271261).
文摘For a generalized radiation problem,an infinitely long submerged horizontal cylinder is forced to vibrate periodically in the transverse direction,with a described elastic harmonic motion along its longitudinal direction.A critical frequency corresponds to the described wave number of elastic vibration,and the generalized hydrodynamic coefficients abruptly change in the vicinity of critical frequency.In this work,a numerical examination is carried out to study the characteristics of wave profiles and wave propagation in the vicinity of the critical frequency.Results show that below the critical frequency,the real parts of complex wave profiles have large values in the vicinity of the cylinder and decay to zero with the increasing distance from the cylinder.Meanwhile,the imaginary parts of complex wave profiles are all zero,which explains why the generalized radiation damping is zero when the vibration is less than the critical frequency.At far distances,no radiation wave is observed.When the vibration exceeds the critical frequency,the real and imaginary parts of the wave profiles oscillate harmonically and keep steady amplitudes.In addition,the generated radiation wave propagates obliquely outward.The influence of the cylinder’s submergence depth on the wave profile is also studied,and the results indicate that the amplitude of the wave profile decreases as the submergence depth of the cylinder increases.The 3D wave profiles are graphically presented to show the wave propagation characteristics in the vicinity of the critical frequency for this generalized radiation problem.This study provides a good reference for the interaction between fluid and slender elastic structures.
文摘BACKGROUND Critical flicker frequency(CFF)is a quantitative tool for assessing hepatic enceph-alopathy(HE),particularly minimal HE,which is associated with poor prognosis in liver cirrhosis.Alcohol-related liver disease(ALD)is a leading global cause of cirrhosis;however,the effects of alcohol on CFF and its relationship with liver stiffness(LS)remain underexplored.AIM To study the impact of alcohol withdrawal on CFF and its correlation with LS in ALD patients.METHODS A total of 108 patients were included:93 heavy drinkers hospitalized for detoxi-fication,15 with non-ALD etiologies,and 20 healthy controls.CFF was measured using the Hepatonorm analyzer,and LS via transient elastography(FibroScan).Baseline and post-detoxification assessments were conducted in 57 ALD patients.RESULTS The cohort had a mean age of 53.7±13.8 years,with 74% male participants.CFF measurements were reliable,with 97.2% of patients showing an interquartile range<20%.ALD patients exhibited significantly lower CFF compared to controls.Receiver operating characteristic analysis for overt HE(n=12)yielded an area under the curve of 0.66(95%confidence interval:0.49-0.84,P=0.0142),with an optimal cutoff of 36.5 Hz.CFF significantly improved post-detoxification.Patients with LS>17 kPa had lower CFF,while those with intermediate LS showed no significant difference.CONCLUSION CFF is influenced by HE severity and acute alcohol exposure,showing improvement after detoxification.Its weak correlation with fibrosis stage suggests that CFF serves as a sensitive neurocognitive marker in ALD.
基金supported by the National Natural Science Foundation of China(NSFC)under Grant 51905483.
文摘Rollover of commercial heavy vehicles can cause enormous economic losses and fatalities.It is easier for such vehicles to rollover if the driver’s steering frequency is close to the critical frequency of the vehicle’s roll motion;however,the critical roll frequency has rarely been investigated.In this study,the second-order transfer function between the steering input and roll angle was developed to calculate the critical frequency of the vehicle’s roll motion.The simulated spectrum and transfer function were then used to dynamically predict the peak lateral load transfer ratio.Laboratory experiments were conducted using a scaled vehicle to verify the critical roll frequency.The results suggest that the peak value of the lateral load transfer ratio during steering can be accurately determined from the driver’s input,and the critical roll frequency has a dominant effect on the dynamic rollover of heavy vehicles.
文摘A model for the negative phase of ionospheric storms in middle latitudes is presented. It is assumed that there will be molecule enriched air in the thermosphere above the auroral oval during the period of the main phase of a magnetic storm. The molecule enriched air is carried to the middle latitudes by thermospheric neutral wind, and at the same time it diffuses away. When the molecule enriched air arrives at the F2 layer above a station, the electron loss rate in the F2 layer increases, the electron density decreases and then the negative phase at the station begins. We have calculated the variations of the fo F2 following magnetic storms for Manzhouli （29.5°N, 117.5°E）, Freiburg （48°N, 07°E） and Billerica （43°N, 71°W） respectively. The results agree very well with typical events observed at the three stations and can be used to explain some average features of negative phase ionospheric storms in middle latitudes.
文摘BACKGROUND:Minimal hepatic encephalopathy (MHE) impairs quality of life and predicts overt hepatic encephalopathy (HE) in cirrhotic patients.Diagnosis of MHE requires cumbersome tests.Lactulose is effective in the treatment of MHE.This study aimed to evaluate the use of critical flicker frequency (CFF) for the diagnosis of MHE in cirrhotic patients after treatment.METHODS:One hundred and ten patients were evaluated by psychometry (number connection tests A,B or figure connection tests A,B),P300 auditory event related potential (P300ERP),venous ammonia,and CFF for MHE.MHE was diagnosed by abnormal psychometry (>2SD age matched controls) and P300ERP.MHE patients were treated with lactulose for one month.Response was defined by normalization (<2SD of matched controls) of both psychometry and P300ERP.RESULTS:Of the 110 patients [Child Turcott Pugh score A:B:C 39:42:29,(age 41.6±11.6 years,M:F 82:28)],75 (68%) had abnormal results of psychometric tests,and 74 (67%) had prolonged P300ERP.Fifteen (20%) patients with abnormal results of psychometric tests had normal P300ERP.Thus sixty (54.5%) patients were diagnosed as having MHE.After treatment for one month,34 (57%) recovered while 26 (43%) continued to have abnormal resents of psychometric or P300ERP tests.CFF was <39 Hz in 72 (65.4%) patients before treatment and in 20 (33.3%) after treatment.CFF sensitivity,specificity,positive predictive value,negative predictive value,and diagnostic accuracy for the assessment of recovery of MHE were 65%,91%,85%,77% and 80%,respectively.CONCLUSION:CFF is a simple,relatively reliable,and accurate test without any dependence on age or literacy in the diagnosis and assessment of recovery of patients with MHE.
文摘With an increase in the density of the seed roll in the roll box of the saw gin, the quality indicators of the fiber and seed are poor, energy consumption increases, machine breakdowns increase, and when the density decreases, the performance of the saw gin increases. Therefore, the density control of the seed roll is one of the important problems in the ginning process. The paper proposes a change in the rotation speed of the saw cylinder with a decrease in the diameter of its numerical linear speed and machine productivity. The article describes the problem of regulating the density of a seed roll in a saw gin of the DP series, provides an overview of work on regulating the operation of the machine, determines the dependence of the productivity of gins and linters on the state of the saw system in these machines, as well as changes in the linear speed of the saw by changing its diameter. Also, the critical speed of the gin and linter saw cylinder was determined to prevent resonance. In this case, the Simulation package of the SolidWorks computer program was used. The results of the study made it possible to adjust the speed of the cylinders when changing the diameter of the saws, which improved the productivity of the machine while maintaining the quality of the fiber and seed.
文摘The effects of the location,number and stiffness of guide pads on the lowest critical rotational frequencies of the rotating circular saw damped at the inside and free at the perimeter are discussed by the non linear theory and the perturbation theory of structural vibration analysis The influence of the centrifugal force and the cutting temperature are considered in the course of the analysis The results of the analysis and the calculation show that the introduction of one guide does not stably raise critical rotational frequencies of the circular saw The two guides can raise lowest critical rotational frequency of the circular saw when the angle between the two guides fixed on the direction of the circumference satisfies the certain conditions
基金support of the Fundamental Research Funds for the Central Universities (SWJTU09ZT24)the National Science Foundation of China (50872116)+1 种基金the PCSIRT of the Ministry of Education of China (IRT0751)the Specialized Research Fund for the Doctoral Program of Higher Education (200806130023)
文摘A theoretical model of describing the electromagnetic and thermal dynamics of high-Tc superconducting bulks in a high-Tc superconducting Maglev system is built up.The model contains the effects of hysteresis-type loss,flux flow,flux creep,and thermal diffusion on the superconducting bulks in the Maglev system.As the first stage of this study,the behavior of magnetic and electric fields,as well as the distribution energy flow density in the superconducting bulk is studied.The results show that the flux flow and thermal diffusion affect the behaviors of the electromagnetic field in the high-Tc superconducting bulks in different ways;however,both of them contribute significantly to the energy dissipation of the superconducting bulks when they are used in the Maglev train.
基金financially supported by Southern Federal University,Russia,2020 Project Vn Gr/2020-03-IF
文摘Despite the continuous improvement of the widely used empirical model international reference ionosphere(IRI),the recently appeared new models must be tested worldwide.Testing along the meridians has the advantage of dealing with the latitudinal dependent parameters.This paper uses new models of parameters foF2(critical frequency),TEC(total electron content),andτ(equivalent slab thickness of the ionosphere),which are of great importance for evaluating the effects of space weather.IRI-Plas,NNT2F2,and NTSM models were tested using data from 6 ionosondes located along the meridian 110°E in March 2012.It is shown that the IRI-Plas model provides the closest values to experiment with respect toτ,while the NTSM model provides a rather limited reflection of the latitude dependence.Analyses of foF2(NNT2F2)have shown that,the NNT2F2 model provides good conformity with experimental values in this area,but it is very dependent on the TEC processing method.The latitudinal dependences of foF2 obtained with TEC and polynomial dependenceτ(Appr)showed the presence of positive deviations from medians not only during disturbances but also quiet periods,longitudinally at the meridian.
文摘In this paper, we use an empirical method to derive the height of maximum electron concentration of the F2 region and the effective meridional neutral wind at Great Wall Station, Antarctica. The meridional wind is also calculated with the HWM90 model. Results can be used to explain two anomaly features of ionosphere at Great Wall Station. In summer, peak values of f0F2 appear during nighttime. In winter, especially during June and July, f0F2 decrease dramatically as compared with summer's one.Summer anomaly can be explained by combining effects of two causes:thermospheric winds and solar radiation. An important reason for the anomaly is the location of Great Wall Station, which is in both high geographic latitude and middle geomagnetic latitude.
基金Supported by CONACYT/UNAM and FUNDACIóN PARA LA SALUD Y LA EDUCACIóN DR. SALVADOR ZUBIRáN A.C (To Macias-Rodriguez RU)CONACYT/UNAM (To Ruiz-Margáin A) Ramón y Cajal Researcher, No. RYC-2014-15242 (To Cubero FJ)
文摘AIM: To evaluate the association between serum concentrations of S100β in patients with cirrhosis and the presence of low grade hepatic encephalopathy (HE).METHODS: This was a cross-sectional study. The population was categorized into four groups healthy subjects, cirrhosis without HE, cirrhosis with covert hepatic encephalopathy (CHE) and cirrhosis with overt HE. Kruskal-Wallis, Mann Whitney’s U with Bonferroni adjustment Spearman correlations and area under the ROC were used as appropriate.RESULTS: A total of 61 subjects were included, 46 cirrhotic patients and 15 healthy volunteers. S100β values were different among all groups, and differences remained significant between groups 1 and 2 (P < 0.001), and also between groups 2 and 3 (P = 0.016), but not between groups 3 and 4. In cirrhotic patients with HE S100β was higher than in patients without HE [0.18 (0.14-0.28) ng/mL vs 0.11 (0.06-0.14) ng/mL, P < 0.001]. There was a close correlation between serum concentrations of S100β and psychometric hepatic encephalopathy score in patients with cirrhosis without HE compared to the patients with cirrhosis with CHE (r = -0.413, P = 0.019). ROC curve analysis yielded > 0.13 ng/mL as the best cutoff value of S100β for the diagnosis of HE (sensitivity 83.3%, specificity 63.6%).CONCLUSION: Serum concentrations of S100β are higher in patients with cirrhosis than in healthy volunteers, and are further increased in the presence of hepatic encephalopathy. The results suggest that serum biomarkers such as S100β could help in the correct characterization of incipient stages of HE.
基金the Program of National Natural Science Foundation of China(No.82070937)(No.81870640)National Natural Science Foundation for Young Scientists of China(No.82000923)(No.82101097).
文摘Background:Due to media opacity,it is usually difficult to accurately evaluate the postoperative visual acuity in cataracts patients.As a small and portable tool,the critical flicker fusion frequency(CFF)device reflects the temporal resolution of visual function and has been widely used in clinical research.However,poor understanding of the technique and equipment limitations have restricted its clinical application in China.Main text:There was a decrease in the CFF value in various ophthalmic diseases,indicating that the CFF is sensitive to detect visual functional changes.A number of studies have shown that the CFF test can accurately distinguish patients with simple cataracts from those with cataracts combined with fundus disease,and,as a visual test,it can more accurately predict postoperative visual acuity without being affected by media opacity.This study comprehensive reviews the basic principles of CFF and its application in ophthalmology,especially in cataracts.Conclusions:As one of the tools for dynamic visual function detection,the CFF test could help doctors to assess the possible presence of fundus disease in cataracts patients,especially in eyes with dense cataracts,and more precisely provide a reasonable visual prognosis than other available visual tests.
文摘Delaminations in structures may significantly reduce the stiffness and strength of the structures and may affect their vibration characteristics. As structural components, beams have been used for various purposes, in many of which beams are often subjected to axial loads and static end moments. In the present study, an analytical solution is developed to study the coupled bending-torsion vibration of a homogeneous beam with a single delamination subjected to axial loads and static end moments. Euler-Bernoulli beam theory and the ＂free mode＂ assumption in delamination vibration are adopted. This is the first study of the influences of static end moments upon the effects of delaminations on natural frequencies, critical buckling loads and critical moments for lateral instability. The results show that the effects of delamination on reducing natural frequencies, critical buckling load and critical moment for lateral instability are aggravated by the presence of static end moment. In turn, the effects of static end moments on vibration and instability characteristics are affected by the presence of delamination. The analytical results of this study can serve as a benchmark for finite element method and other numerical solutions.
文摘Minimal hepatic encephalopathy(MHE)is a critical neurocognitive complication of decompensated liver cirrhosis and portosystemic shunting,which results in a wide range of cognitive deficits including impairments in working attention,psychomotor speed,and executive function.Current guidelines have recommended paper-and-pencil psychometric tests for the diagnosis of MHE.Most high-risk cirrhotic patients are required to be examined;however,paperand-pencil psychometric tests are neither convenient nor rapid to perform in the clinic.Recently,novel computerized psychometric tests,including the inhibitory control test,EncephalApp Stroop App,and critical flicker frequency,have been proven to be rapid,effective,and convenient methods for screening MHE in clinical practice and for identifying high-risk cirrhotic patients for further validation using rigid neuropsychometric examinations.However,diagnostic accuracy of these tests is influenced by educational background,age,and cultural differences.This review summarizes clinical evidence of the application of novel computerized psychometric tests for screening MHE.
文摘The purpose of this study was to assess the effects of reducing driving fatigue with magnitopuncture stimuli on Dazhui (DU14) point and Neiguan (PC6) points using heart rate (HR), reaction time (RT) testing, critical flicker fusion frequency (CFF) and subjective evaluation. Twenty healthy subjects were randomly divided into two groups: A-group (study group) and B-group (control group). All subjects were required to be well rested before the experiment. The subjects were engaged in high speed driving at a constant vehicle velocity of 80 km/h continuously for three hours on a test course simulating an expressway. During the driving magnitopunctures were applied to the Dazhui (DU14) point and Neiguan (PC6) points for the A-group when the subject performed the task for two and half hours, and for the B-group magnitopunctures were applied to non-acupuncture points at the same time session. In this study RT exbited a significant delay in B-group (P<0.01) but no found in A-group after the driving task. CFF and subjective evaluation also exhibited significant differences between the two groups after the driving task (P<0.05). The findings showed that magnitopuncture stimuli on Dazhui (DU14) point and Neiguan (PC6) points could reduce the effects of driving fatigue.
基金National Key Research and Development Program(2018YFE0113900).
文摘Purpose:To investigate the application of critical flicker fusion frequency(CFF)in demyelinating optic neuritis(DON).Methods:A cross-sectional study.A total of 127 eyes in 69 DON patients and 63 eyes in 33 healthy control(HC)groups were included between January 2021 to September 2021 from Department of Ophthalmology,PLA General Hospital.Patients underwent best-corrected visual acuity(BCVA),visual field,optical coherence tomography(OCT),flash visual evoked potential(F-VEP),and CFF examinations.The affected eyes were divided into aquaporins 4(AQP4-),myelin oligodendrocyte glycoprotein(MOG-),and double negative DON according to serum antibody;mild,moderate,severe degree visual impairment according to BCVA0.5,0.1-0.5,<0.1;and 4 groups:<1,1~<3,3~<6 and>6 months according to time interval from onset to CFF examination.One-way ANOVA was used to perform above subgroup analysis.The correlations between CFF and F-VEP peak time,peak value,BCVA and mean visual filed defect(MD)were analyzed in order via Pearson correlation analysis.Results:he trichromatic values of red,green,and yellow in DON affected eyes were 21.83±9.03,23.66±10.21,24.09±10.77 Hz,respectively,which was significantly reduced compared with the HC group(t=-14.82,-14.22,-14.00;P<0.001).The subgroup analysis showed no significant difference between different antibody subtypes(P=0.914<0.848<0.604),whereas,a significant decrease of CFF trichromatic value was found in severe visual acuity impairment group(P<0.001).There was a significant difference in CFF-trichromatic values at different time points(P<0.001),to be specific,CFF fluctuated under 20Hz within 3 months after onset and tended to be stable around 24-28Hz.Correlation analysis showed that the peak time of F-VEP(r=-0.486,-0.515,-0.526;P<0.001),BVCA(r=-0.640,-0.659,-0.642;P<0.001),were negatively correlated with CFF trichromatic values,MD and CFF were positively correlated(r=0.486,0.453,0.476;P=0.003,0.006,0.004).Conclusions:A significant decrease of CFF value was found in DON-affected eyes,and it has a good correlation with BCVA,MD and latency of F-VEP,and can better reflect the impairment of visual function.
基金supported by the National Natural Science Foundation of China (Grant Nos. 40804042 and 41074115)the Post Doctor Foundation of China (Grant No. 200902445)the Fundamental Research Funds for the Central Universities (Grant No. 4081004)
文摘The vertical ionogram can provide the important ionospheric parameters, such as critical frequency, virtual height and electron density, for ionospheric research. The oblique ionosonde has the ability to detect the ionosphere over sea and other terrain where it is not practical to deploy vertical sounder and provide more ionograms with less transmitting and receiving devices. Therefore, the conversion of the oblique ionogram to vertical ionogram for obtaining the important ionospheric parameters is a very useful inversion technology. The experimental comparison between oblique and vertical detections was carried out in the equatorial ionospheric anomaly (EIA) region of south China on 25 and 26 August 2010. The oblique detecting path was from Wuhan to Shenzhen and the VI ionosonde was located in the midpoint of the oblique path. The oblique ionogram reversion results showed a small deviation of the critical frequency, minimum virtual height as well as the electron density profile of the ionospheric F layer, as compared with the real vertical observations.
基金Project supported by the National Basic Research Program(Grant No :2005CB422303),the National Natural ScienceFoundation of China(Grant Nos :40333030 ,40506007 and 90411010)
文摘The analysis of the satellite altimeter data suggests that the propagating speed of intraseasonal long Rossby wave amplified in the subtropical Pacific Ocean is faster than that of first mode baroclinic free Rossby wave predicted by the liner theory and the propagating speed of intrascasonal long Rossby wave reflected in the eastern boundary of Pacific Ocean agrees basically with the liner theory speed of first mode baroelinic free P, ossby wave. If we do not distinguish the two kinds of hmg Rossby waves and estimate the Rossby wave speed in the whole basin, the phase speed is merely 25% higher than the linear theory long Rossby wave speed. The acceleration of the propagating speed of intraseasonal long Rossby wave amplified in the subtropical Pacific Ocean is due to the existence of westward thermolcline mean flow.
基金supported by the projects of Chinese Academy of Sciences(Grant No.KZZD-EW-01-3)the National Basic Research Program of China(Grant No.2012CB825604)the National Natural Science Foundation of China(Grant Nos.41231065,41174137,41321003)
文摘Nighttime enhancements in ionospheric electron density at mid- and low-latitudes are investigated by using the critical frequency of the F2-1ayer （foF2） data measured from ionosonde stations at Okinawa （26.3°N, 127.8°E, Geomagnetic 15.3°N）, Yamagawa （31.2°N, 130.6°E, Geomagnetic 20.4°N）, Kokubunji （35.7°N, 139.5°E, Geomagnetic 25.5°N）, and Wakkanai （45.4°N, 141.7°E, Geomagnetic 35.4°N） in East Asia during several solar cycles. The results show that there are obvious seasonal and solar activity dependencies of the nighttime electron density enhancements. The enhancements are termed pre-midnight enhancement and post-midnight enhancement, according to the local time when the enhancement appeared. The former has a higher occurrence probability in summer months than in winter months. In contrast, the latter has a larger occurrence probability in winter months than in summer months. Moreover, the nighttime enhancements in electron density are more likely to occur at lower solar activity. These seasonal and solar activity variations of the nighttime enhancements in electron density can be explained in terms of the combined effects of downward plasma flux from the plasmasphere and the neutral winds.
基金the Universidad Nacional de San Luis(grant 03-2718)National Scientific and Technical Research Council of Argentina(CONICET).
文摘The vibration of dusty surfaces inevitably causes re-entrainment of particles into the atmosphere.Given that movement of mineral dust particles deposited on a surface begins at a critical frequency (fc) and amplitude,an experimental laboratory study was conducted to determine the onset conditions for resuspension of a vibrated granular soil.We determined the resuspension state diagram as a function of frequency and amplitude of a sinusoidal vibration,the granulometry of the dust and the thickness of the soil bed.The mitigation effect of humidity was also evaluated.Critical frequencies ranged between 2.5 and 23 Hz when amplitudes were less than 12 rmm.These results were independent of bed thickness and perturbation type.For all particle sizes observed,fc decreased monotonically with A,contrasting with behavior observed for individual particles.In dry samples,fe for large size classes was markedly less when A was greater than 6 mm;while thefc for fine fractions only decreased once amplitudes reached 10 mm.Experiments with wet granular soils demonstrated that wetting above an optimum humidity did not necessarily impede movement and caused agglomeration.This study provides guidelines for managing resuspension of granular soils subjected to vibrations.
