1,195 research outputs found
Boundary layer physics over snow and ice
Observations of the unique chemical environment over snow and ice in recent decades, particularly in the polar regions. have stimulated increasing interest in the boundary layer processes that mediate exchanges between the ice/snow interface and the atmosphere. This paper provides a review of the underlying concepts and examples from recent field studies in polar boundary layer meteorology, which will generally apply to atmospheric flow over snow and ice surfaces. It forms a companion paper to the chemistry review papers in this special issue of ACP that focus on processes linking halogens to the depletion of boundary layer ozone in coastal environments, mercury transport and deposition, snow photochemistry, and related snow physics. In this context, observational approaches, stable boundary layer behavior, the effects of a weak or absent diurnal cycle, and transport and mixing over the heterogeneous surfaces characteristic of coastal ocean environments are of particular relevance
Sialic acid content of erythrocytes in normal individuals and patients with certain hematologic disorders
The sialic acid content of erythrocytes from healthy individuals of different blood types and of patients with known hematological disorders has been determined. The sialic acid was completely released enzymatically with sialidase and quantitated by the thiobarbituric acid method. The sialic acid content of erythrocytes was constant irrespective of ABO blood type, or anticoagulant used; viz, 0.85â0.92 mÌmoles/ml of packed erythrocytes or 46â53 Ă 10 6 sialyl residues per cell. Deviations from these normal values were obtained with erythrocytes from patients with a variety of hematological disorders. Patients with the following disorders have significantly (P < 0.01) lower sialic acid values compared to erythrocytes from healthy individuals (given in the order of decreasing sialic acid content): sickle cell anemia, acute lymphocytic leukemia, chronic lymphocytic leukemia, acute myelomonocytic leukemia, nonâHodgkin lymphocytic lymphoma, chronic granulocytic leukemia, acute myelocytic leukemia, leukemia, and Hodgkin disease.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/101840/1/2830090405_ftp.pd
Computational techniques for the assessment of fracture repair
The combination of high-resolution three-dimensional medical imaging, increased computing power, and modern computational methods provide unprecedented capabilities for assessing the repair and healing of fractured bone. Fracture healing is a natural process that restores the mechanical integrity of bone and is greatly influenced by the prevailing mechanical environment. Mechanobiological theories have been proposed to provide greater insight into the relationships between mechanics (stress and strain) and biology. Computational approaches for modelling these relationships have evolved from simple tools to analyze fracture healing at a single point in time to current models that capture complex biological events such as angiogenesis, stochasticity in cellular activities, and cell-phenotype specific activities. The predictive capacity of these models has been established using corroborating physical experiments. For clinical application, mechanobiological models accounting for patient-to-patient variability hold the potential to predict fracture healing and thereby help clinicians to customize treatment. Advanced imaging tools permit patient-specific geometries to be used in such models. Refining the models to study the strain fields within a fracture gap and adapting the models for case-specific simulation may provide more accurate examination of the relationship between strain and fracture healing in actual patients. Medical imaging systems have significantly advanced the capability for less invasive visualization of injured musculoskeletal tissues, but all too often the consideration of these rich datasets has stopped at the level of subjective observation. Computational image analysis methods have not yet been applied to study fracture healing, but two comparable challenges which have been addressed in this general area are the evaluation of fracture severity and of fracture-associated soft tissue injury. CT-based methodologies developed to assess and quantify these factors are described and results presented to show the potential of these analysis methods
Loading of a Rb magneto-optic trap from a getter source
We study the properties of a Rb magneto-optic trap loaded from a commercial
getter source which provides a large flux of atoms for the trap along with the
capability of rapid turn-off necessary for obtaining long trap lifetimes. We
have studied the trap loading at two different values of background pressure to
determine the cross-section for Rb--N collisions to be 3.5(4)x10^{-14} cm^2
and that for Rb--Rb collisions to be of order 3x10^{-13} cm^2. At a background
pressure of 1.3x10^{-9} torr, we load more than 10^8 atoms into the trap with a
time constant of 3.3 s. The 1/e lifetime of trapped atoms is 13 s limited only
by background collisions.Comment: 5 pages, 5 figure
Being More Realistic About Reasons: On Rationality and Reasons Perspectivism
This paper looks at whether it is possible to unify the
requirements of rationality with the demands of normative
reasons. It might seem impossible to do because one depends
upon the agentâs perspective and the other upon features of
the situation. Enter Reasons Perspectivism. Reasons
perspectivists think they can show that rationality does consist
in responding correctly to reasons by placing epistemic
constraints on these reasons. They think that if normative
reasons are subject to the right epistemic constraints, rational
requirements will correspond to the demands generated by
normative reasons. While this proposal is prima facie plausible,
it cannot ultimately unify reasons and rationality. There is no
epistemic constraint that can do what reasons perspectivists
would need it to do. Some constraints are too strict. The rest
are too slack. This points to a general problem with the
reasons-first program. Once we recognize that the agentâs
epistemic position helps determine what she should do, we
have to reject the idea that the features of the agentâs situation
can help determine what we should do. Either rationality
crowds out reasons and their demands or the reasons will make
unreasonable demands
Tannakian duality for Anderson-Drinfeld motives and algebraic independence of Carlitz logarithms
We develop a theory of Tannakian Galois groups for t-motives and relate this
to the theory of Frobenius semilinear difference equations. We show that the
transcendence degree of the period matrix associated to a given t-motive is
equal to the dimension of its Galois group. Using this result we prove that
Carlitz logarithms of algebraic functions that are linearly independent over
the rational function field are algebraically independent.Comment: 39 page
Study of Dipole Resonance Strength in 12-C via the Reactions 12-C(pol.p,p'c)
This research was sponsored by the National Science Foundation Grant NSF PHY-931478
An ansatz for the nonlinear Demkov-Kunike problem for cold molecule formation
We study nonlinear mean-field dynamics of ultracold molecule formation in the
case when the external field configuration is defined by the level-crossing
Demkov-Kunike model, characterized by a bell-shaped coupling and finite
variation of the detuning. Analyzing the fast sweep rate regime of the strong
interaction limit, which models a situation when the peak value of the coupling
is large enough and the resonance crossing is sufficiently fast, we construct a
highly accurate ansatz to describe the temporal dynamics of the molecule
formation in the mentioned interaction regime. The absolute error of the
constructed approximation is less than 3*10^-6 for the final transition
probability while at certain time points it might increase up to 10^-3.
Examining the role of the different terms in the constructed approximation, we
prove that in the fast sweep rate regime of the strong interaction limit the
temporal dynamics of the atom-molecule conversion effectively consists of the
process of resonance crossing, which is governed by a nonlinear equation,
followed by atom-molecular coherent oscillations which are basically described
by a solution of the linear problem, associated with the considered nonlinear
one.Comment: Accepted for publication in J. Contemp. Phys. (Armenian National
Academy of Sciences) 8 pages, 4 figure
Evidence for hadronic deconfinement in -p collisions at 1.8 TeV
We have measured deconfined hadronic volumes, fm,
produced by a one dimensional (1D) expansion. These volumes are directly
proportional to the charged particle pseudorapidity densities . The hadronization temperature is (syst)
MeV. Using Bjorken's 1D model,the hadronization energy density is (stat) GeV/fm corresponding to an excitation of (stat) quark-gluon degrees of freedom.Comment: 15 pages, 3 figures, 2 table
Evaporative cooling of trapped fermionic atoms
We propose an efficient mechanism for the evaporative cooling of trapped
fermions directly into quantum degeneracy. Our idea is based on an electric
field induced elastic interaction between trapped atoms in spin symmetric
states. We discuss some novel general features of fermionic evaporative cooling
and present numerical studies demonstrating the feasibility for the cooling of
alkali metal fermionic species Li, K, and Rb. We also
discuss the sympathetic cooling of fermionic hyperfine spin mixtures, including
the effects of anisotropic interactions.Comment: to be publishe
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