The purpose of this paper is to seek a connection between noncommutative geometry, an offshoot of string theory, and certain aspects of dark matter and dark energy. The former case is based on a simple mathematical ar...The purpose of this paper is to seek a connection between noncommutative geometry, an offshoot of string theory, and certain aspects of dark matter and dark energy. The former case is based on a simple mathematical argument showing that the main manifestation of dark matter in connection with flat galactic rotation curves is also a consequence of noncommutative geometry. The latter case requires an examination of the local effect of noncommutative geometry and the subsequent extension to the global phenomenon of an accelerating Universe.展开更多
Clinical engineering(CE) has evolved rapidly over the last 25 years in China. Among the 34 provincial-level administrative units within China, the Zhejiang Province is one of the most advanced in terms of healthcare t...Clinical engineering(CE) has evolved rapidly over the last 25 years in China. Among the 34 provincial-level administrative units within China, the Zhejiang Province is one of the most advanced in terms of healthcare technology maintenance and management. In order to determine Zhejiang's current stage of development and opportunities for further improvement, a comparison of the performance of its CE departments was made against hospitals in the USA. Data were collected from 21 Zhejiang hospitals and compared to those from 270 acute-care hospitals in USA collected by Truven Health Analytics. The benchmarking comparison was made in three categories: operational, financial, and productivity. Within the operational category, the following metrics were compared: equipment inventory size/operating beds, annual repairs/inventory size, and annual scheduled maintenance/inventory size. Within the Financial category, the following metrics were compared: total CE expense/operating beds and total CE expense/total hospital expense. Within the Productivity category, the following metrics were compared: total CE full-time equivalent(FTE)/inventory size and total CE FTE/total hospital expense. These comparisons showed that:(1) While the equipment inventory in Zhejiang tends to be much smaller than USA for hospitals of comparable amount of operating beds, the numbers of repairs and scheduled maintenance per inventory size are similar;(2) The total CE expense/total hospital expense ratio is around 1% in both Zhejiang and USA; however, the total CE expense/operating beds and total CE expense/cost of equipment inventory are significantly lower in Zhejiang than USA;(3) The FTE amount in Zhejiang is significantly higher than in USA relative to both inventory size and total hospital operating expense, but significantly lower relative to the number of operating beds. The fact that repairs and scheduled maintenance are similar in Zhejiang and USA shows that CE leaders are managing equipment in comparable manner. Most of the differences found in the comparisons were traced to a few factors. First, the average length of stay in China is substantially higher than USA, which explains why hospitals in Zhejiang tend to have more operating beds but fewer pieces of equipment. Second, labor cost is significantly lower in China than USA, thus allowing Zhejiang hospitals to employ more workers than their American counterparts. Third, there is significantly difference in the cost of living between China and USA; Finally, being public entities Chinese hospitals are managed and operated in a different manner than American hospitals, which are mostly private, albeit nonprofit organizations. Nonetheless, it is interesting to note that hospitals in both areas spend roughly 1% of their total expenditure for CE. The results suggest that CE in Zhejiang is comparable to USA in terms of managerial excellence but there could be some room for improvement in financial management and productivity.展开更多
This paper discusses the effect that conformal symmetry can have on a charged wormhole. The analysis yields a physical interpretation of the conformal factor in terms of the electric charge. The rate of change of the ...This paper discusses the effect that conformal symmetry can have on a charged wormhole. The analysis yields a physical interpretation of the conformal factor in terms of the electric charge. The rate of change of the conformal factor determines much of the outcome, which ranges from having no solution to wormholes having either one or two throats.展开更多
It is shown in the first part of this paper that a combined model comprising ordinary and quintessential matter can support a traversable wormhole in Einstein-Maxwell gravity. Since the solution allows zero tidal forc...It is shown in the first part of this paper that a combined model comprising ordinary and quintessential matter can support a traversable wormhole in Einstein-Maxwell gravity. Since the solution allows zero tidal forces, the wormhole is suitable for a humanoid traveler. The second part of the paper shows that the electric field can be eliminated (Einstein gravity), but only by tolerating enormous tidal forces. Such a wormhole would still be capable of transmitting signals.展开更多
This article develops a procedure for screening variables, in ultra high-di- mensional settings, based on their predictive significance. This is achieved by ranking the variables according to the variance of their res...This article develops a procedure for screening variables, in ultra high-di- mensional settings, based on their predictive significance. This is achieved by ranking the variables according to the variance of their respective marginal regression functions (RV-SIS). We show that, under some mild technical conditions, the RV-SIS possesses a sure screening property, which is defined by Fan and Lv (2008). Numerical comparisons suggest that RV-SIS has competitive performance compared to other screening procedures, and outperforms them in many different model settings.展开更多
This paper discusses the feasibility of thin-shell wormholes in spacetimes of embedding class one admitting a one-parameter group of conformal motions. It is shown that the surface energy density σis positive, while ...This paper discusses the feasibility of thin-shell wormholes in spacetimes of embedding class one admitting a one-parameter group of conformal motions. It is shown that the surface energy density σis positive, while the surface pressure is negative, resulting in , thereby signaling a violation of the null energy condition, a necessary condition for holding a wormhole open. For a Morris-Thorne wormhole, matter that violates the null energy condition is referred to as “exotic”. For the thin-shell wormholes in this paper, however, the violation has a physical explanation since it is a direct consequence of the embedding theory in conjunction with the assumption of conformal symmetry. These properties avoid the need to hypothesize the existence of the highly problematical exotic matter.展开更多
The idea of an oscillating Universe has remained a topic of interest even after the discovery of dark energy. This paper confirms this idea by means of another well-established theory in general relativity, the embedd...The idea of an oscillating Universe has remained a topic of interest even after the discovery of dark energy. This paper confirms this idea by means of another well-established theory in general relativity, the embedding of curved spacetimes in higher-dimensional flat spacetimes: an n-dimensional Riemannian space is said to be of embedding class m if m +n is the lowest dimension of the flat space in which the given space can be embedded;here . So a four-dimensional Riemannian space is of class two and can therefore be embedded in a six-dimensional flat space. A line element of class two can be reduced to a line element of class one by a suitable coordinate transformation. The extra dimension can be either spacelike or timelike, leading to accelerating and decelerating expansions, respectively. Accordingly, it is proposed in this paper that the free parameter occurring in the transformation be a periodic function of time. The result is a mathematical model that can be interpreted as a periodic change in the signature of the embedding space. This signature change may be the best model for an oscillating Universe and complements various models proposed in the literature.展开更多
The main goal of this paper is to determine the effect of an extra dimension on a traversable wormhole. Here an earlier study by the author [Phys. Rev. D 98, 064041 (2018)] is extended in several significant ways. To ...The main goal of this paper is to determine the effect of an extra dimension on a traversable wormhole. Here an earlier study by the author [Phys. Rev. D 98, 064041 (2018)] is extended in several significant ways. To begin with, the extra spatial dimension is assumed to be time dependent, while the redshift and shape functions, as well as the extra dimension, are functions of both r and l, the respective radial and extra coordinates;the last of these is therefore a function of r, l, and t. The main objective is to determine the conditions that allow the throat of the wormhole to be threaded with ordinary matter (by respecting the null energy condition) and that the same conditions lead to a violation of the null energy condition in the fifth dimension, which is therefore responsible for sustaining the wormhole. The dependence of the extra dimension on l and t is subject to additional conditions that are subsequently analyzed in this paper. Finally, the extra dimension may be extremely small or even curled up.展开更多
Cyber-physical systems (CPS) represent a class of complex engineered systems where functionality and behavior emerge through the interaction between the computational and physical domains. Simulation provides design e...Cyber-physical systems (CPS) represent a class of complex engineered systems where functionality and behavior emerge through the interaction between the computational and physical domains. Simulation provides design engineers with quick and accurate feedback on the behaviors generated by their designs. However, as systems become more complex, simulating their behaviors becomes computation all complex. But, most modern simulation environments still execute on a single thread, which does not take advantage of the processing power available on modern multi-core CPUs. This paper investigates methods to partition and simulate differential equation-based models of cyber-physical systems using multiple threads on multi-core CPUs that can share data across threads. We describe model partitioning methods using fixed step and variable step numerical in-tegration methods that consider the multi-layer cache structure of these CPUs to avoid simulation performance degradation due to cache conflicts. We study the effectiveness of each parallel simu-lation algorithm by calculating the relative speedup compared to a serial simulation applied to a series of large electric circuit models. We also develop a series of guidelines for maximizing performance when developing parallel simulation software intended for use on multi-core CPUs.展开更多
While wormholes are as good a prediction of Einstein’s theory as black holes, they are subject to severe restrictions from quantum field theory. In particular, holding a wormhole open requires a violation of the null...While wormholes are as good a prediction of Einstein’s theory as black holes, they are subject to severe restrictions from quantum field theory. In particular, holding a wormhole open requires a violation of the null energy condition, calling for the existence of exotic matter. The Casimir effect has shown that this physical requirement can be met on a small scale, thereby solving a key conceptual problem. The Casimir effect does not, however, guarantee that the small-scale violation is sufficient for supporting a macroscopic wormhole. The purpose of this paper is to connect the Casimir effect to noncommutative geometry, which also aims to accommodate small-scale effects, the difference being that these can now be viewed as intrinsic properties of spacetime. As a result, the noncommutative effects can be implemented by modifying only the energy momentum tensor in the Einstein field equations, while leaving the Einstein tensor unchanged. The wormhole can therefore be macroscopic in spite of the small Casimir effect.展开更多
When Morris and Thorne first proposed that wormholes might be actual physical structures suitable for interstellar travel, they needed to pay close attention to certain traversability conditions such as low tidal forc...When Morris and Thorne first proposed that wormholes might be actual physical structures suitable for interstellar travel, they needed to pay close attention to certain traversability conditions such as low tidal forces, which placed severe constraints on the wormhole geometry. Even more problematical was the need for “exotic matter” resulting from the unavoidable violation of the null energy condition required to hold a wormhole open. The purpose of this paper is to overcome these problems by starting with the charged wormhole model of Kim and Lee and assuming a noncommutative-geometry background: the violation of the null energy condition can be attributed to the latter, while the electric charge allows the reduction of the tidal forces to acceptable levels without invoking the trivial zero-tidal-force assumption.展开更多
The starting point in this note is f(R) modified gravity in a cosmological setting. We assume a spatially flat universe to describe late-time cosmology and the perfect-fluid equation of state to model the hypothesized...The starting point in this note is f(R) modified gravity in a cosmological setting. We assume a spatially flat universe to describe late-time cosmology and the perfect-fluid equation of state to model the hypothesized dark energy. Given that on a cosmological scale, f(R) modified gravity must remain close to Einstein gravity to be consistent with observation, it was concluded that either (1) Einstein’s cosmological constant was the only acceptable model for the accelerated expansion, or that (2) the equation of state for dark energy was far more complicated than the perfect-fluid model and might even exclude a constant w.展开更多
It was shown earlier by Rahaman et al. that a noncommutative-geometry background can account for galactic rotation curves without the need for dark matter. The smearing effect that characterizes noncommutative geometr...It was shown earlier by Rahaman et al. that a noncommutative-geometry background can account for galactic rotation curves without the need for dark matter. The smearing effect that characterizes noncommutative geometry is described by means of a Gaussian distribution intended to replace the Dirac delta function. The purpose of this paper is two-fold: 1) to account for the galactic rotation curves in a more transparent and intuitively more appealing way by replacing the Gaussian function by the simpler Lorentzian distribution proposed by Nozari and Mehdipour and 2) to show that the smearing effect is both a necessary and sufficient condition for meeting the stability criterion.展开更多
The Brouwer fixed-point theorem in topology states that for any continuous mapping <em>f</em> on a compact convex set into itself admits a fixed point, <em>i.e.</em>, a point <em>x</em...The Brouwer fixed-point theorem in topology states that for any continuous mapping <em>f</em> on a compact convex set into itself admits a fixed point, <em>i.e.</em>, a point <em>x</em><sub>0</sub> such that<em> f</em>(<em>x</em><sub>0</sub>) = <em>x</em><sub>0</sub>. Under suitable conditions, this fixed point corresponds to the throat of a traversable wormhole, <em>i.e.</em>, <em>b</em>(<em>r</em><sub>0</sub>) = <em>r</em><sub>0</sub> for the shape function <em>b</em> = <em>b</em>(<em>r</em>). The possible existence of wormholes can therefore be deduced from purely mathematical considerations without going beyond the existing physical requirements.展开更多
Modified Newtonian dynamics (MOND) is a hypothesized modification of Newton’s law of universal gravitation to account for the flat rotation curves in the outer regions of galaxies, thereby eliminating the need for da...Modified Newtonian dynamics (MOND) is a hypothesized modification of Newton’s law of universal gravitation to account for the flat rotation curves in the outer regions of galaxies, thereby eliminating the need for dark matter. Although a highly successful model, it is not a self-contained physical theory since it is based entirely on observations. It is proposed in this paper that noncommutative geometry, an offshoot of string theory, can account for the flat rotation curves and thereby provide an explanation for MOND. This paper extends an earlier heuristic argument by the author.展开更多
While wormholes are just as good a prediction of Einstein’s theory as black holes, they are subject to severe restrictions from quantum field theory. To allow for the possibility of interstellar travel, a macroscopic...While wormholes are just as good a prediction of Einstein’s theory as black holes, they are subject to severe restrictions from quantum field theory. To allow for the possibility of interstellar travel, a macroscopic wormhole would need to maintain sufficiently low radial tidal forces. It is proposed in this paper that the assumption of zero tidal forces, i.e., the limiting case, is sufficient for overcoming the restrictions from quantum field theory. The feasibility of this approach is subsequently discussed by 1) introducing the additional conditions needed to ensure that the radial tidal forces can indeed be sufficiently low and 2) by viewing traversable wormholes as emergent phenomena, thereby increasing the likelihood of their existence.展开更多
In spite of their speculative nature,traversable wormholes are a topic of interest that started with the Einstein-Rosen bridge in 1935 and became a major research area with the introduction of the Morris-Thorne wormho...In spite of their speculative nature,traversable wormholes are a topic of interest that started with the Einstein-Rosen bridge in 1935 and became a major research area with the introduction of the Morris-Thorne wormhole in 1988.It also became apparent in time that such wormholes are likely to be compact stellar objects,akin to neutron stars.Although widely discussed,wormholes having a low energy density may therefore not be massive enough to exist on a macroscopic scale.Important examples are wormholes based on a noncommutative geometry background and wormholes supported by the negative energy density sourced by the Casimir effect.The main goal of this paper is to invoke f(Q)modified gravity to provide the extra degrees of freedom to help overcome these obstacles.展开更多
Hyperspectral photothermal mid-infrared spectroscopic imaging(HP-MIRSI)is an emerging technology with promising applications in cervical cancer diagnosis and quantitative,label-free histopathology.This study pioneers ...Hyperspectral photothermal mid-infrared spectroscopic imaging(HP-MIRSI)is an emerging technology with promising applications in cervical cancer diagnosis and quantitative,label-free histopathology.This study pioneers the application of HP-MIRSI to the evaluation of clinical cervical cancer tissues,achieving excellent tissue type segmentation accuracy of over 95%.This achievement stems from an integrated approach of optimized data acquisition,computational data reconstruction,and the application of machine learning algorithms.The results are statistically robust,drawing from tissue samples of 98 cervical cancer patients and incorporating over 40 million data points.Traditional cervical cancer diagnosis methods entail biopsy,staining,and visual evaluation by a pathologist.This process is qualitative,subject to variations in staining and subjective interpretations,and requires extensive tissue processing,making it costly and time-consuming.In contrast,our proposed alternative can produce images comparable to those from histological analyses without the need for staining or complex sample preparation.This label-free,quantitative method utilizes biochemical data from HPMIRSI and employs machine-learning algorithms for the rapid and precise segmentation of cervical tissue subtypes.This approach can potentially transform histopathological analysis by offering a more accurate and label-free alternative to conventional diagnostic processes.展开更多
文摘The purpose of this paper is to seek a connection between noncommutative geometry, an offshoot of string theory, and certain aspects of dark matter and dark energy. The former case is based on a simple mathematical argument showing that the main manifestation of dark matter in connection with flat galactic rotation curves is also a consequence of noncommutative geometry. The latter case requires an examination of the local effect of noncommutative geometry and the subsequent extension to the global phenomenon of an accelerating Universe.
文摘Clinical engineering(CE) has evolved rapidly over the last 25 years in China. Among the 34 provincial-level administrative units within China, the Zhejiang Province is one of the most advanced in terms of healthcare technology maintenance and management. In order to determine Zhejiang's current stage of development and opportunities for further improvement, a comparison of the performance of its CE departments was made against hospitals in the USA. Data were collected from 21 Zhejiang hospitals and compared to those from 270 acute-care hospitals in USA collected by Truven Health Analytics. The benchmarking comparison was made in three categories: operational, financial, and productivity. Within the operational category, the following metrics were compared: equipment inventory size/operating beds, annual repairs/inventory size, and annual scheduled maintenance/inventory size. Within the Financial category, the following metrics were compared: total CE expense/operating beds and total CE expense/total hospital expense. Within the Productivity category, the following metrics were compared: total CE full-time equivalent(FTE)/inventory size and total CE FTE/total hospital expense. These comparisons showed that:(1) While the equipment inventory in Zhejiang tends to be much smaller than USA for hospitals of comparable amount of operating beds, the numbers of repairs and scheduled maintenance per inventory size are similar;(2) The total CE expense/total hospital expense ratio is around 1% in both Zhejiang and USA; however, the total CE expense/operating beds and total CE expense/cost of equipment inventory are significantly lower in Zhejiang than USA;(3) The FTE amount in Zhejiang is significantly higher than in USA relative to both inventory size and total hospital operating expense, but significantly lower relative to the number of operating beds. The fact that repairs and scheduled maintenance are similar in Zhejiang and USA shows that CE leaders are managing equipment in comparable manner. Most of the differences found in the comparisons were traced to a few factors. First, the average length of stay in China is substantially higher than USA, which explains why hospitals in Zhejiang tend to have more operating beds but fewer pieces of equipment. Second, labor cost is significantly lower in China than USA, thus allowing Zhejiang hospitals to employ more workers than their American counterparts. Third, there is significantly difference in the cost of living between China and USA; Finally, being public entities Chinese hospitals are managed and operated in a different manner than American hospitals, which are mostly private, albeit nonprofit organizations. Nonetheless, it is interesting to note that hospitals in both areas spend roughly 1% of their total expenditure for CE. The results suggest that CE in Zhejiang is comparable to USA in terms of managerial excellence but there could be some room for improvement in financial management and productivity.
文摘This paper discusses the effect that conformal symmetry can have on a charged wormhole. The analysis yields a physical interpretation of the conformal factor in terms of the electric charge. The rate of change of the conformal factor determines much of the outcome, which ranges from having no solution to wormholes having either one or two throats.
文摘It is shown in the first part of this paper that a combined model comprising ordinary and quintessential matter can support a traversable wormhole in Einstein-Maxwell gravity. Since the solution allows zero tidal forces, the wormhole is suitable for a humanoid traveler. The second part of the paper shows that the electric field can be eliminated (Einstein gravity), but only by tolerating enormous tidal forces. Such a wormhole would still be capable of transmitting signals.
文摘This article develops a procedure for screening variables, in ultra high-di- mensional settings, based on their predictive significance. This is achieved by ranking the variables according to the variance of their respective marginal regression functions (RV-SIS). We show that, under some mild technical conditions, the RV-SIS possesses a sure screening property, which is defined by Fan and Lv (2008). Numerical comparisons suggest that RV-SIS has competitive performance compared to other screening procedures, and outperforms them in many different model settings.
文摘This paper discusses the feasibility of thin-shell wormholes in spacetimes of embedding class one admitting a one-parameter group of conformal motions. It is shown that the surface energy density σis positive, while the surface pressure is negative, resulting in , thereby signaling a violation of the null energy condition, a necessary condition for holding a wormhole open. For a Morris-Thorne wormhole, matter that violates the null energy condition is referred to as “exotic”. For the thin-shell wormholes in this paper, however, the violation has a physical explanation since it is a direct consequence of the embedding theory in conjunction with the assumption of conformal symmetry. These properties avoid the need to hypothesize the existence of the highly problematical exotic matter.
文摘The idea of an oscillating Universe has remained a topic of interest even after the discovery of dark energy. This paper confirms this idea by means of another well-established theory in general relativity, the embedding of curved spacetimes in higher-dimensional flat spacetimes: an n-dimensional Riemannian space is said to be of embedding class m if m +n is the lowest dimension of the flat space in which the given space can be embedded;here . So a four-dimensional Riemannian space is of class two and can therefore be embedded in a six-dimensional flat space. A line element of class two can be reduced to a line element of class one by a suitable coordinate transformation. The extra dimension can be either spacelike or timelike, leading to accelerating and decelerating expansions, respectively. Accordingly, it is proposed in this paper that the free parameter occurring in the transformation be a periodic function of time. The result is a mathematical model that can be interpreted as a periodic change in the signature of the embedding space. This signature change may be the best model for an oscillating Universe and complements various models proposed in the literature.
文摘The main goal of this paper is to determine the effect of an extra dimension on a traversable wormhole. Here an earlier study by the author [Phys. Rev. D 98, 064041 (2018)] is extended in several significant ways. To begin with, the extra spatial dimension is assumed to be time dependent, while the redshift and shape functions, as well as the extra dimension, are functions of both r and l, the respective radial and extra coordinates;the last of these is therefore a function of r, l, and t. The main objective is to determine the conditions that allow the throat of the wormhole to be threaded with ordinary matter (by respecting the null energy condition) and that the same conditions lead to a violation of the null energy condition in the fifth dimension, which is therefore responsible for sustaining the wormhole. The dependence of the extra dimension on l and t is subject to additional conditions that are subsequently analyzed in this paper. Finally, the extra dimension may be extremely small or even curled up.
文摘Cyber-physical systems (CPS) represent a class of complex engineered systems where functionality and behavior emerge through the interaction between the computational and physical domains. Simulation provides design engineers with quick and accurate feedback on the behaviors generated by their designs. However, as systems become more complex, simulating their behaviors becomes computation all complex. But, most modern simulation environments still execute on a single thread, which does not take advantage of the processing power available on modern multi-core CPUs. This paper investigates methods to partition and simulate differential equation-based models of cyber-physical systems using multiple threads on multi-core CPUs that can share data across threads. We describe model partitioning methods using fixed step and variable step numerical in-tegration methods that consider the multi-layer cache structure of these CPUs to avoid simulation performance degradation due to cache conflicts. We study the effectiveness of each parallel simu-lation algorithm by calculating the relative speedup compared to a serial simulation applied to a series of large electric circuit models. We also develop a series of guidelines for maximizing performance when developing parallel simulation software intended for use on multi-core CPUs.
文摘While wormholes are as good a prediction of Einstein’s theory as black holes, they are subject to severe restrictions from quantum field theory. In particular, holding a wormhole open requires a violation of the null energy condition, calling for the existence of exotic matter. The Casimir effect has shown that this physical requirement can be met on a small scale, thereby solving a key conceptual problem. The Casimir effect does not, however, guarantee that the small-scale violation is sufficient for supporting a macroscopic wormhole. The purpose of this paper is to connect the Casimir effect to noncommutative geometry, which also aims to accommodate small-scale effects, the difference being that these can now be viewed as intrinsic properties of spacetime. As a result, the noncommutative effects can be implemented by modifying only the energy momentum tensor in the Einstein field equations, while leaving the Einstein tensor unchanged. The wormhole can therefore be macroscopic in spite of the small Casimir effect.
文摘When Morris and Thorne first proposed that wormholes might be actual physical structures suitable for interstellar travel, they needed to pay close attention to certain traversability conditions such as low tidal forces, which placed severe constraints on the wormhole geometry. Even more problematical was the need for “exotic matter” resulting from the unavoidable violation of the null energy condition required to hold a wormhole open. The purpose of this paper is to overcome these problems by starting with the charged wormhole model of Kim and Lee and assuming a noncommutative-geometry background: the violation of the null energy condition can be attributed to the latter, while the electric charge allows the reduction of the tidal forces to acceptable levels without invoking the trivial zero-tidal-force assumption.
文摘The starting point in this note is f(R) modified gravity in a cosmological setting. We assume a spatially flat universe to describe late-time cosmology and the perfect-fluid equation of state to model the hypothesized dark energy. Given that on a cosmological scale, f(R) modified gravity must remain close to Einstein gravity to be consistent with observation, it was concluded that either (1) Einstein’s cosmological constant was the only acceptable model for the accelerated expansion, or that (2) the equation of state for dark energy was far more complicated than the perfect-fluid model and might even exclude a constant w.
文摘It was shown earlier by Rahaman et al. that a noncommutative-geometry background can account for galactic rotation curves without the need for dark matter. The smearing effect that characterizes noncommutative geometry is described by means of a Gaussian distribution intended to replace the Dirac delta function. The purpose of this paper is two-fold: 1) to account for the galactic rotation curves in a more transparent and intuitively more appealing way by replacing the Gaussian function by the simpler Lorentzian distribution proposed by Nozari and Mehdipour and 2) to show that the smearing effect is both a necessary and sufficient condition for meeting the stability criterion.
文摘The Brouwer fixed-point theorem in topology states that for any continuous mapping <em>f</em> on a compact convex set into itself admits a fixed point, <em>i.e.</em>, a point <em>x</em><sub>0</sub> such that<em> f</em>(<em>x</em><sub>0</sub>) = <em>x</em><sub>0</sub>. Under suitable conditions, this fixed point corresponds to the throat of a traversable wormhole, <em>i.e.</em>, <em>b</em>(<em>r</em><sub>0</sub>) = <em>r</em><sub>0</sub> for the shape function <em>b</em> = <em>b</em>(<em>r</em>). The possible existence of wormholes can therefore be deduced from purely mathematical considerations without going beyond the existing physical requirements.
文摘Modified Newtonian dynamics (MOND) is a hypothesized modification of Newton’s law of universal gravitation to account for the flat rotation curves in the outer regions of galaxies, thereby eliminating the need for dark matter. Although a highly successful model, it is not a self-contained physical theory since it is based entirely on observations. It is proposed in this paper that noncommutative geometry, an offshoot of string theory, can account for the flat rotation curves and thereby provide an explanation for MOND. This paper extends an earlier heuristic argument by the author.
文摘While wormholes are just as good a prediction of Einstein’s theory as black holes, they are subject to severe restrictions from quantum field theory. To allow for the possibility of interstellar travel, a macroscopic wormhole would need to maintain sufficiently low radial tidal forces. It is proposed in this paper that the assumption of zero tidal forces, i.e., the limiting case, is sufficient for overcoming the restrictions from quantum field theory. The feasibility of this approach is subsequently discussed by 1) introducing the additional conditions needed to ensure that the radial tidal forces can indeed be sufficiently low and 2) by viewing traversable wormholes as emergent phenomena, thereby increasing the likelihood of their existence.
文摘In spite of their speculative nature,traversable wormholes are a topic of interest that started with the Einstein-Rosen bridge in 1935 and became a major research area with the introduction of the Morris-Thorne wormhole in 1988.It also became apparent in time that such wormholes are likely to be compact stellar objects,akin to neutron stars.Although widely discussed,wormholes having a low energy density may therefore not be massive enough to exist on a macroscopic scale.Important examples are wormholes based on a noncommutative geometry background and wormholes supported by the negative energy density sourced by the Casimir effect.The main goal of this paper is to invoke f(Q)modified gravity to provide the extra degrees of freedom to help overcome these obstacles.
基金supported in part by the Cancer Prevention and Research Institute of Texas(CPRIT)no.RR170075(RR)National Institutes of Health(NIH)grant no.R01DK135870 and no.R01HL173597(RR)+2 种基金NLM Training Program in Biomedical Informatics and Data Science no.T15LM007093(RR and SB)National Institutes of Health no.R01HL146745(DM)the National Science Foundation CAREER Award no.1943455(DM).
文摘Hyperspectral photothermal mid-infrared spectroscopic imaging(HP-MIRSI)is an emerging technology with promising applications in cervical cancer diagnosis and quantitative,label-free histopathology.This study pioneers the application of HP-MIRSI to the evaluation of clinical cervical cancer tissues,achieving excellent tissue type segmentation accuracy of over 95%.This achievement stems from an integrated approach of optimized data acquisition,computational data reconstruction,and the application of machine learning algorithms.The results are statistically robust,drawing from tissue samples of 98 cervical cancer patients and incorporating over 40 million data points.Traditional cervical cancer diagnosis methods entail biopsy,staining,and visual evaluation by a pathologist.This process is qualitative,subject to variations in staining and subjective interpretations,and requires extensive tissue processing,making it costly and time-consuming.In contrast,our proposed alternative can produce images comparable to those from histological analyses without the need for staining or complex sample preparation.This label-free,quantitative method utilizes biochemical data from HPMIRSI and employs machine-learning algorithms for the rapid and precise segmentation of cervical tissue subtypes.This approach can potentially transform histopathological analysis by offering a more accurate and label-free alternative to conventional diagnostic processes.
