910 research outputs found
Passenger Flows in Underground Railway Stations and Platforms, MTI Report 12-43
Urban rail systems are designed to carry large volumes of people into and out of major activity centers. As a result, the stations at these major activity centers are often crowded with boarding and alighting passengers, resulting in passenger inconvenience, delays, and at times danger. This study examines the planning and analysis of station passenger queuing and flows to offer rail transit station designers and transit system operators guidance on how to best accommodate and manage their rail passengers. The objectives of the study are to: 1) Understand the particular infrastructural, operational, behavioral, and spatial factors that affect and may constrain passenger queuing and flows in different types of rail transit stations; 2) Identify, compare, and evaluate practices for efficient, expedient, and safe passenger flows in different types of station environments and during typical (rush hour) and atypical (evacuations, station maintenance/ refurbishment) situations; and 3) Compile short-, medium-, and long-term recommendations for optimizing passenger flows in different station environments
On 2D Viscoelasticity with Small Strain
An exact two-dimensional rotation-strain model describing the motion of
Hookean incompressible viscoelastic materials is constructed by the polar
decomposition of the deformation tensor. The global existence of classical
solutions is proved under the smallness assumptions only on the size of initial
strain tensor. The proof of global existence utilizes the weak dissipative
mechanism of motion, which is revealed by passing the partial dissipation to
the whole system.Comment: Different contributions of strain and rotation of the deformation are
studied for viscoelastic fluids of Oldroyd-B type in 2
Blow-up of the hyperbolic Burgers equation
The memory effects on microscopic kinetic systems have been sometimes
modelled by means of the introduction of second order time derivatives in the
macroscopic hydrodynamic equations. One prototypical example is the hyperbolic
modification of the Burgers equation, that has been introduced to clarify the
interplay of hyperbolicity and nonlinear hydrodynamic evolution. Previous
studies suggested the finite time blow-up of this equation, and here we present
a rigorous proof of this fact
Designing and Operating Safe and Secure Transit Systems: Assessing Current Practices in the United States and Abroad, MTI Report 04-05
Public transit systems around the world have for decades served as a principal venue for terrorist acts. Today, transit security is widely viewed as an important public policy issue and is a high priority at most large transit systems and at smaller systems operating in large metropolitan areas. Research on transit security in the United States has mushroomed since 9/11; this study is part of that new wave of research. This study contributes to our understanding of transit security by (1) reviewing and synthesizing nearly all previously published research on transit terrorism; (2) conducting detailed case studies of transit systems in London, Madrid, New York, Paris, Tokyo, and Washington, D.C.; (3) interviewing federal officials here in the United States responsible for overseeing transit security and transit industry representatives both here and abroad to learn about efforts to coordinate and finance transit security planning; and (4) surveying 113 of the largest transit operators in the United States. Our major findings include: (1) the threat of transit terrorism is probably not universal—most major attacks in the developed world have been on the largest systems in the largest cities; (2) this asymmetry of risk does not square with fiscal politics that seek to spread security funding among many jurisdictions; (3) transit managers are struggling to balance the costs and (uncertain) benefits of increased security against the costs and (certain) benefits of attracting passengers; (4) coordination and cooperation between security and transit agencies is improving, but far from complete; (5) enlisting passengers in surveillance has benefits, but fearful passengers may stop using public transit; (6) the role of crime prevention through environmental design in security planning is waxing; and (7) given the uncertain effectiveness of antitransit terrorism efforts, the most tangible benefits of increased attention to and spending on transit security may be a reduction in transit-related person and property crimes
Recommended from our members
Optimization of Tetrapolar Impedance Electrodes in Microfluidic Devices for Point of Care Diagnostics using Finite Element Modeling
Electrophoresis is widely applied in the field of biochemistry and molecular biology. Tetrapolar electrical impedance sensing (TEIS) has been shown capable of replacing the conventional detection technology in order to develop a point of care electrophoretic analyzer. Besides the advantages of reduced influence of electrode polarization, TEIS is affected by sensitivity distribution depending on the electrode design. A well reported practice outside of electrophoresis, systematic investigation of the effects of sensitivity distribution on the TEIS in microfluidic devices has not been conducted. Here we utilize finite element modeling, backed by experimental results, to optimize the sensor design within an electrophoretic separation device. Numerous sensor designs were validated regarding detectability, sensitivity and spatial resolution. The results show, that minimizing the distance between the central/pick-up electrodes increases sensitivity and spatial resolution whereas the distance between the central electrodes and the outer electrode do not influence sensitivity and spatial resolution
Global exponential stability of classical solutions to the hydrodynamic model for semiconductors
In this paper, the global well-posedness and stability of classical solutions
to the multidimensional hydrodynamic model for semiconductors on the framework
of Besov space are considered. We weaken the regularity requirement of the
initial data, and improve some known results in Sobolev space. The local
existence of classical solutions to the Cauchy problem is obtained by the
regularized means and compactness argument. Using the high- and low- frequency
decomposition method, we prove the global exponential stability of classical
solutions (close to equilibrium). Furthermore, it is also shown that the
vorticity decays to zero exponentially in the 2D and 3D space. The main
analytic tools are the Littlewood-Paley decomposition and Bony's para-product
formula.Comment: 18 page
Global Solutions for Incompressible Viscoelastic Fluids
We prove the existence of both local and global smooth solutions to the
Cauchy problem in the whole space and the periodic problem in the n-dimensional
torus for the incompressible viscoelastic system of Oldroyd-B type in the case
of near equilibrium initial data. The results hold in both two and three
dimensional spaces. The results and methods presented in this paper are also
valid for a wide range of elastic complex fluids, such as magnetohydrodynamics,
liquid crystals and mixture problems.Comment: We prove the existence of global smooth solutions to the Cauchy
problem for the incompressible viscoelastic system of Oldroyd-B type in the
case of near equilibrium initial dat
Quantifying Chaos in Models of the Solar Neighbourhood
{} {To quantify the amount of chaos that exists in the local phase space.} {A
sample of orbits from four different models of the Solar neighbourhood phase
space are analysed by a new chaos identification (and quantification)
technique. While three of the used models bear the signature of the
perturbation due to both the Galactic bar and the spiral pattern, the last of
the models is a bar only one. We explore the models by inter-comparing the
corresponding values of chaos strength that is induced at the various energy
levels .}{(1) We find that of all the viable models that have been demonstrated
to successfully reproduce the local phase space structure, i.e. those that
include the bar as well as the spiral, bear strong chaoticity, though the model
that implies the highest degree of chaos is the one in which overlap of the
major resonances of the bar and the spiral occurs. The bar only model is found
to display regularity. (2) We advance chaos to be primarily responsible for the
splitting of the Hyades-Pleiades mode (the larger mode) of the local velocity
distribution}{}Comment: 6 pages; 4 figures; accepted for publication in Astronomy &
Astrophysic
A comparison of strength and power characteristics prior to anterior cruciate ligament rupture and at the end of rehabilitation in professional soccer players
Background: Strength and power is often reduced on the involved vs. contralateral limb and healthy controls following anterior cruciate ligament (ACL) reconstruction but no study has compared to pre-injury values at the time of return to sport (RTS).
Hypothesis: Divergent recovery patterns in strength and power characteristics will be present at RTS relative to pre-injury baseline data and healthy matched controls.
Study design: Cohort study
Level of evidence: Level 3
Methods: Isokinetic strength tests, bilateral and single leg countermovement jumps (CMJ; SLCMJ) were measured prior to ACL rupture in 20 professional soccer players. These then had surgical reconstruction (ACL group) and completed follow up testing prior to RTS. Healthy controls (uninjured group) were tested at the same time as the ACL group pre-injury. Values recorded at RTS of the ACL group were compared to pre-injury. We also compared the uninjured and ACL groups at baseline and RTS.
Results: Compared to pre-injury, ACL normalised quadriceps peak torque of the involved limb (% difference = -7%), SLCMJ height (% difference = -12.08%) and Reactive Strength Index modified (RSImod) (% difference = -5.04%) were reduced following ACL reconstruction. No significant reductions in CMJ height, RSImod and relative peak power were indicated at RTS in the ACL group when compared to pre-injury values but deficits were present relative to controls. The uninvolved limb significantly improved quadriceps (% difference = 9.34%) and hamstring strength (% difference = 7.36%) from pre-injury to RTS. No significant differences from baseline were shown in SLCMJ height, power and reactive strength of the uninvolved limb following ACL reconstruction.
Conclusion: Strength and power in professional soccer players at RTS following ACL reconstruction were often reduced compared to preinjury values and matched healthy controls.
Clinical relevance: Deficits were more apparent in the SLCMJ suggesting dynamic and multijoint unilateral force production is an important component of rehabilitation. Use of the uninvolved limb and normative data to determine recovery may not always be appropriate
Concerning the Wave equation on Asymptotically Euclidean Manifolds
We obtain KSS, Strichartz and certain weighted Strichartz estimate for the
wave equation on , , when metric
is non-trapping and approaches the Euclidean metric like with
. Using the KSS estimate, we prove almost global existence for
quadratically semilinear wave equations with small initial data for
and . Also, we establish the Strauss conjecture when the metric is radial
with for .Comment: Final version. To appear in Journal d'Analyse Mathematiqu
- …