This study aims to introduce a novel hybrid design with a combination of two more common mechanisms for improving the capacity of systems in absorbing the kinetic energy of moving vehicles or devices. This new model c...This study aims to introduce a novel hybrid design with a combination of two more common mechanisms for improving the capacity of systems in absorbing the kinetic energy of moving vehicles or devices. This new model consists of two individual mechanisms, i.e., expansion of a circular tube accompanied by crushing of an inner tube, which dissipate the energy through friction, plastic deformations and failures of inner tube. This study comprises 24 case studies surveyed under two different design controls, constant mass and constant volume, for comparing purposes. Finite element simulations are utilized so as to investigate models’ deformations and to extract some crashworthiness parameters in aid of representing the efficiency of the mechanism as well as conducting a parametric study between three different profiles of inner tube. This study shows that models with inner circular and hexagonal tube profile absorb higher amount of energy due to experiencing three different modes of energy dissipation systems, including folding, shear and ductile damages.展开更多
BACKGROUND Dysfunctional beliefs about sleep may influence academic performance through their impact on sleep quality.Differences in chronotype can further moderate this relationship,particularly among students with i...BACKGROUND Dysfunctional beliefs about sleep may influence academic performance through their impact on sleep quality.Differences in chronotype can further moderate this relationship,particularly among students with irregular sleep patterns.AIM To examine the indirect effects of dysfunctional beliefs about sleep on academic performance through sleep quality while considering individual differences in chronotypes among medical students.METHODS The participants were categorized by chronotype and administered the Dysfunctional Beliefs and Attitudes about Sleep Scale and the Pittsburgh Sleep Quality Index and reported their grade point averages(GPAs).Mediation analysis was performed to examine indirect pathways through sleep quality.RESULTS Dysfunctional sleep beliefs did not directly affect academic success but indirectly impaired GPA via reduced sleep quality,especially in evening-type students.CONCLUSION Chronotype moderates the relationship between sleep quality and academic performance, highlighting the need for targeted cognitive interventions.展开更多
Recently,multilevel diffractive lenses(MDLs)have attracted considerable attention,mainly due to their superior wave-focusing performance;however,efforts to reduce chromatic aberration are still ongoing.Here,we present...Recently,multilevel diffractive lenses(MDLs)have attracted considerable attention,mainly due to their superior wave-focusing performance;however,efforts to reduce chromatic aberration are still ongoing.Here,we present a numerical design and experimentally demonstrate a high-numerical aperture(∼0.99),diffraction-limited achromatic multilevel diffractive lens(AMDL),operating in the microwave range of 10–14 GHz.A multi-objective differential evolution(MO-DE)algorithm was incorporated with the three-dimensional(3D)finite-difference time-domain method to optimize the heights and widths of each concentric ring(zone)of the AMDL structure.To the best of our knowledge for the first time,in this study,the desired focal distance was also treated as an optimization parameter in addition to the structural parameters of the zones.Thus,MO-DE diminishes the necessity of predetermined focal distance and center wavelength by also providing an alternative method for phase profile tailoring.The proposed AMDL can be considered an ultra-compact and flat lens since it has the radius of 3.7λ_(c) and a thickness of∼λ_(c),whereλ_(c) is the center wavelength of 24.98 mm(i.e.,12 GHz).The numerically calculated full width at half maximum values are<0.554λand focusing efficiency values are varying between 28%and 45.5%.To experimentally demonstrate the functionality of the optimized lens,the AMDL composed of polylactic acid material polymer is fabricated via 3D-printing technology.The numerical and experimental results are compared,discussed in detail,and observed to be in good agreement.Moreover,the verified AMDL in the microwave regime is scaled down to the visible wavelengths to observe achromatic and diffraction-limited focusing behavior between 380 and 620 nm wavelengths.展开更多
In this paper, a technique was numerically implemented to generate a frequency shift keying （FSK） radio-over-fiber （RoF） signal in optical domain. Due to the oscillator free generation of FSK signal, this scheme i...In this paper, a technique was numerically implemented to generate a frequency shift keying （FSK） radio-over-fiber （RoF） signal in optical domain. Due to the oscillator free generation of FSK signal, this scheme is highly stable with reduced complexity and extremely cost effective. The remote heterodyne detection method was used to detect the signal, where beating occurs to detect the FSK signal. With this scheme, it is able to efficiently generate FSK signal in the range of 60 and 75 GHz at 8 Gbit/s and effectively transmit it over 80 km link without degrading the signal shape and quality. The nonlinear threshold （NLT） point of the system has also been numerically analyzed to estimate the nonlinear tolerance of the system. Besides, the impact of transmission distance and polarization mode dispersion （PMD） was evaluated. Furthermore, the wavelength reuse for the uplink was implemented in the scheme by reusing the same wave- length for uplink that was used for signal generation at downlink. The whole process was performed in optical domain. Thus this scheme is very cost effective as the overall architecture of RoF system is simplified.展开更多
In this paper,we report on the performance comparison of all-optical signal processing methodologies to compensate fiber transmission impairments,namely chromatic dispersion and nonlinear distortion caused by the Ker...In this paper,we report on the performance comparison of all-optical signal processing methodologies to compensate fiber transmission impairments,namely chromatic dispersion and nonlinear distortion caused by the Kerr effect,in a coherent 112 Gbit∕s dual-polarization 64 bit quadrature amplitude modulation system over 800 km standard single-mode fiber.We numerically compare optical backward propagation(OBP)with optical phase conjugation(OPC)techniques,namely.mid-link spectral inversion,predispersed spectral inversion,and OPC with nonlinearity module.We also evaluate a self-phase-modulation-based optical limiter with an appropriate prechirping to compensate for the intensity fluctuations as a hybrid approach with OBP.The results depict improvement in system performance by a factor of∼4 dB of signal input power by all-optical signal processing methods,which is comparative with ideal digital backward propagation where the high complexity is the intrinsic impediment in the real-time implementation of the technique with coherent receivers.展开更多
Beyond resource efficiencies,green buildings aim to create healthy indoor environments for building occupants.In terms of improving occupant well-being,a unique case emerges for healthcare facilities,whose patients ma...Beyond resource efficiencies,green buildings aim to create healthy indoor environments for building occupants.In terms of improving occupant well-being,a unique case emerges for healthcare facilities,whose patients may be at a vulnerable state.In the U.S.,the Leadership in Energy and Environmental Design(LEED)rating system has become the most widely recognized certification system for green buildings,including green healthcare facilities and buildings.Hospitals with high total scores in the LEED rating system are green buildings but may not necessarily be the optimal green healthcare environment from a patient’s wellbeing perspective.Certified healthcare facilities were analyzed in terms of their credit valuation to assess whether healthcare facilities prioritize specific criteria that influence patient wellbeing and recovery time.Analysis of results indicate hospitals may be valuing the level of certification more than those credits that were deemed relevant for patient wellbeing and rate of recovery,either due to lack of information or due to economic constraints.To consolidate the previous results and to compare the performance of LEED certified green hospitals to the national average,the Hospital Consumer Assessment of Healthcare Providers and Systems(HCAHPS)survey was analyzed for patients’perspectives on the healthcare facility.Results indicate higher satisfaction in green hospitals’overall patient care performance as well as a greater tendency to recommend green hospitals to others compared to the national average.No statistical significance was found for hospital cleanliness and quietness between green hospitals and the national average.展开更多
文摘This study aims to introduce a novel hybrid design with a combination of two more common mechanisms for improving the capacity of systems in absorbing the kinetic energy of moving vehicles or devices. This new model consists of two individual mechanisms, i.e., expansion of a circular tube accompanied by crushing of an inner tube, which dissipate the energy through friction, plastic deformations and failures of inner tube. This study comprises 24 case studies surveyed under two different design controls, constant mass and constant volume, for comparing purposes. Finite element simulations are utilized so as to investigate models’ deformations and to extract some crashworthiness parameters in aid of representing the efficiency of the mechanism as well as conducting a parametric study between three different profiles of inner tube. This study shows that models with inner circular and hexagonal tube profile absorb higher amount of energy due to experiencing three different modes of energy dissipation systems, including folding, shear and ductile damages.
文摘BACKGROUND Dysfunctional beliefs about sleep may influence academic performance through their impact on sleep quality.Differences in chronotype can further moderate this relationship,particularly among students with irregular sleep patterns.AIM To examine the indirect effects of dysfunctional beliefs about sleep on academic performance through sleep quality while considering individual differences in chronotypes among medical students.METHODS The participants were categorized by chronotype and administered the Dysfunctional Beliefs and Attitudes about Sleep Scale and the Pittsburgh Sleep Quality Index and reported their grade point averages(GPAs).Mediation analysis was performed to examine indirect pathways through sleep quality.RESULTS Dysfunctional sleep beliefs did not directly affect academic success but indirectly impaired GPA via reduced sleep quality,especially in evening-type students.CONCLUSION Chronotype moderates the relationship between sleep quality and academic performance, highlighting the need for targeted cognitive interventions.
基金TED University Scientific Research Project(T-19-B2010-90016)support of KAIST Startup Funding(Project number G04200054).
文摘Recently,multilevel diffractive lenses(MDLs)have attracted considerable attention,mainly due to their superior wave-focusing performance;however,efforts to reduce chromatic aberration are still ongoing.Here,we present a numerical design and experimentally demonstrate a high-numerical aperture(∼0.99),diffraction-limited achromatic multilevel diffractive lens(AMDL),operating in the microwave range of 10–14 GHz.A multi-objective differential evolution(MO-DE)algorithm was incorporated with the three-dimensional(3D)finite-difference time-domain method to optimize the heights and widths of each concentric ring(zone)of the AMDL structure.To the best of our knowledge for the first time,in this study,the desired focal distance was also treated as an optimization parameter in addition to the structural parameters of the zones.Thus,MO-DE diminishes the necessity of predetermined focal distance and center wavelength by also providing an alternative method for phase profile tailoring.The proposed AMDL can be considered an ultra-compact and flat lens since it has the radius of 3.7λ_(c) and a thickness of∼λ_(c),whereλ_(c) is the center wavelength of 24.98 mm(i.e.,12 GHz).The numerically calculated full width at half maximum values are<0.554λand focusing efficiency values are varying between 28%and 45.5%.To experimentally demonstrate the functionality of the optimized lens,the AMDL composed of polylactic acid material polymer is fabricated via 3D-printing technology.The numerical and experimental results are compared,discussed in detail,and observed to be in good agreement.Moreover,the verified AMDL in the microwave regime is scaled down to the visible wavelengths to observe achromatic and diffraction-limited focusing behavior between 380 and 620 nm wavelengths.
文摘In this paper, a technique was numerically implemented to generate a frequency shift keying （FSK） radio-over-fiber （RoF） signal in optical domain. Due to the oscillator free generation of FSK signal, this scheme is highly stable with reduced complexity and extremely cost effective. The remote heterodyne detection method was used to detect the signal, where beating occurs to detect the FSK signal. With this scheme, it is able to efficiently generate FSK signal in the range of 60 and 75 GHz at 8 Gbit/s and effectively transmit it over 80 km link without degrading the signal shape and quality. The nonlinear threshold （NLT） point of the system has also been numerically analyzed to estimate the nonlinear tolerance of the system. Besides, the impact of transmission distance and polarization mode dispersion （PMD） was evaluated. Furthermore, the wavelength reuse for the uplink was implemented in the scheme by reusing the same wave- length for uplink that was used for signal generation at downlink. The whole process was performed in optical domain. Thus this scheme is very cost effective as the overall architecture of RoF system is simplified.
文摘In this paper,we report on the performance comparison of all-optical signal processing methodologies to compensate fiber transmission impairments,namely chromatic dispersion and nonlinear distortion caused by the Kerr effect,in a coherent 112 Gbit∕s dual-polarization 64 bit quadrature amplitude modulation system over 800 km standard single-mode fiber.We numerically compare optical backward propagation(OBP)with optical phase conjugation(OPC)techniques,namely.mid-link spectral inversion,predispersed spectral inversion,and OPC with nonlinearity module.We also evaluate a self-phase-modulation-based optical limiter with an appropriate prechirping to compensate for the intensity fluctuations as a hybrid approach with OBP.The results depict improvement in system performance by a factor of∼4 dB of signal input power by all-optical signal processing methods,which is comparative with ideal digital backward propagation where the high complexity is the intrinsic impediment in the real-time implementation of the technique with coherent receivers.
文摘Beyond resource efficiencies,green buildings aim to create healthy indoor environments for building occupants.In terms of improving occupant well-being,a unique case emerges for healthcare facilities,whose patients may be at a vulnerable state.In the U.S.,the Leadership in Energy and Environmental Design(LEED)rating system has become the most widely recognized certification system for green buildings,including green healthcare facilities and buildings.Hospitals with high total scores in the LEED rating system are green buildings but may not necessarily be the optimal green healthcare environment from a patient’s wellbeing perspective.Certified healthcare facilities were analyzed in terms of their credit valuation to assess whether healthcare facilities prioritize specific criteria that influence patient wellbeing and recovery time.Analysis of results indicate hospitals may be valuing the level of certification more than those credits that were deemed relevant for patient wellbeing and rate of recovery,either due to lack of information or due to economic constraints.To consolidate the previous results and to compare the performance of LEED certified green hospitals to the national average,the Hospital Consumer Assessment of Healthcare Providers and Systems(HCAHPS)survey was analyzed for patients’perspectives on the healthcare facility.Results indicate higher satisfaction in green hospitals’overall patient care performance as well as a greater tendency to recommend green hospitals to others compared to the national average.No statistical significance was found for hospital cleanliness and quietness between green hospitals and the national average.
