2,496 research outputs found
Different Melting Behavior in Pentane and Heptane Monolayers on Graphite; Molecular Dynamics Simulations
Molecular dynamics simulations are utilized to study the melting transition
in pentane (C5H12) and heptane (C7H16), physisorbed onto the basal plane of
graphite at near-monolayer coverages. Through use of the newest, optimized
version of the anisotropic united-atom model (AUA4) to simulate both systems at
two separate coverages, this study provides evidence that the melting
transition for pentane and heptane monolayers are significantly different.
Specifically, this study proposes a very rapid transition from the solid
crystalline rectangular-centered (RC) phase to a fluid phase in pentane
monolayers, whereas heptane monolayers exhibit a slower transition that
involves a more gradual loss of RC order in the solid-fluid phase transition.
Through a study of the melting behavior, encompassing variations where the
formation of gauche defects in the alkyl chains are eliminated, this study
proposes that this gradual melting behavior for heptane monolayers is a result
of less orientational mobility of the heptane molecules in the solid RC phase,
as compared to the pentane molecules. This idea is supported through a study of
a nonane monolayer, which gives the gradual melting signature that heptane
monolayers also seem to indicate. The results of this work are compared to
previous experiment over pentane and heptane monolayers, and are found to be in
good agreement
Introductory Physics: Writing scheme teaches science to non-scientists
DOI: 10.1088/0031-9120/42/6/F05 http://iopscience.iop.org/0031-9120/42/6/F05/pdf/0031-9120_42_6_F05.pdfWriting-intensive activities can be made use of to implement a 'narrow-but-deep' approach in an undergraduate introductory physics course for non-science majors. In this approach, a carefully selected number of topics are treated not only in more detail but also with attention to developing
them logically and rigorously. We teach a course that utilizes parts of an interdisciplinary text by Alan Lightman [1] and focuses on three subjects: (i) the conservation of energy, (ii) the second law of thermodynamics and (iii) the special theory of relativity
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"Perhaps Irrelevant". The Iconography of Tycho Brahe's Small Gilt Brass Quadrant.
When Tycho Brahe published a description of his astronomical instruments in 1598 as part of a strategy to procure royal patronage, it was not with one of his grander, precision measurement tools that he opened his account, but rather a small brass quadrant with limited observational utility. The defining feature of this instrument was seemingly a small emblematic image inscribed within the arc of the quadrant. Through this symbolic motif Tycho conveyed a moralising message about the relative worth of astronomy. Considering a range of visual productions that may have influenced his iconography, the present paper situates the quadrant within the broader context of Renaissance visual culture and examines the significance of the quadrant in Tycho's wider instrument collection.Emma Perkins’ research was made possible through the generous support of an AHRC doctoral award.This is the accepted manuscript. The final version is available from Brill at http://booksandjournals.brillonline.com/content/journals/10.1163/18253911-03001002
Relativistic Acoustic Geometry
Sound wave propagation in a relativistic perfect fluid with a non-homogeneous
isentropic flow is studied in terms of acoustic geometry. The sound wave
equation turns out to be equivalent to the equation of motion for a massless
scalar field propagating in a curved space-time geometry. The geometry is
described by the acoustic metric tensor that depends locally on the equation of
state and the four-velocity of the fluid. For a relativistic supersonic flow in
curved space-time the ergosphere and acoustic horizon may be defined in a way
analogous the non-relativistic case. A general-relativistic expression for the
acoustic analog of surface gravity has been found.Comment: 14 pages, LaTe
Phase Transitions in Hexane Monolayers Physisorbed onto Graphite
We report the results of molecular dynamics (MD) simulations of a complete
monolayer of hexane physisorbed onto the basal plane of graphite. At low
temperatures the system forms a herringbone solid. With increasing temperature,
a solid to nematic liquid crystal transition takes place at K
followed by another transition at K into an isotropic fluid.
We characterize the different phases by calculating various order parameters,
coordinate distributions, energetics, spreading pressure and correlation
functions, most of which are in reasonable agreement with available
experimental evidence. In addition, we perform simulations where the
Lennard-Jones interaction strength, corrugation potential strength and dihedral
rigidity are varied in order to better characterize the nature of the two
transitions through. We find that both phase transitions are facilitated by a
``footprint reduction'' of the molecules via tilting, and to a lesser degree
via creation of gauche defects in the molecules.Comment: 18 pages, eps figures embedded, submitted to Phys. Rev.
Lensing Properties of Lightlike Current Carrying Cosmic Strings
The lensing properties of superconducting cosmic strings endowed with a time
dependent pulse of lightlike current are investigated. The metric outside the
core of the string belongs to the --wave class, with a deficit angle. We
study the field theoretic bosonic Witten model coupled to gravity, and we show
that the full metric (both outside and inside the core) is a Taub-Kerr-Shild
generalization of that for the static string with no current. It is shown that
the double image due to the deficit angle evolves in an unambiguous way as a
pulse of lightlike current passes between the source and the observer.
Observational consequences of this signature of the existence of cosmic strings
are briefly discussed.Comment: 21 pages, LaTeX-REVTeX, 7 figures available upon request, preprint #
DAMTP-R94/1
Sodium-Glucose Cotransporter-2 Inhibitor Use is Associated with a Reduced Risk of Heart Failure Hospitalization in Patients with Heart Failure with Preserved Ejection Fraction and Type 2 Diabetes Mellitus: A Real-World Study on a Diverse Urban Population
Background: Limited evidence-based therapies exist for the management of heart failure with preserved ejection fraction (HFpEF). Sodium-glucose cotransporter-2 inhibitor (SGLT2i) use in patients with systolic heart failure (HFrEF) and type-2-diabetes mellitus (T2DM) is associated with improved cardiovascular (CV) and renal outcomes. Objective: We sought to examine whether there is an association of SGLT2i use with improved CV outcomes in patients with HFpEF. Patients and methods: We conducted a single-center, retrospective review of patients with HFpEF and T2DM. The cohort was divided into two groups based on prescription of a SGLT2i or sitagliptin. The primary outcome was heart failure hospitalization (HFH); secondary outcomes were all-cause hospitalization and acute kidney injury (AKI). Results: After propensity score matching, there were 250 patients (89 in the SGLT2i group, 161 in the sitagliptin group), with a mean follow-up of 295 days. Univariate Cox regression analysis showed that the SGLT2i group had a reduced risk of HFH versus the sitagliptin group (hazard ratio (HR) 0.13; 95% confidence interval (CI) (0.05–0.36); p \u3c 0.001). The SGLT2i group had a decreased risk of all-cause hospitalization (HR 0.48; 95% CI (0.33–0.70); p \u3c 0.001) and SGLT2i had a lower risk of AKI (HR 0.39; 95% CI (0.20–0.74); p = 0.004). Conclusions: The use of SGLT2is is associated with a reduced incidence of HFH and AKI in patients with HFpEF and T2DM
Modified Boltzmann Transport Equation and Freeze Out
We study Freeze Out process in high energy heavy ion reaction. The
description of the process is based on the Boltzmann Transport Equation (BTE).
We point out the basic limitations of the BTE approach and introduce Modified
BTE. The Freeze Out dynamics is presented in the 4-dimensional space-time in a
layer of finite thickness, and we employ Modified BTE for the realistic Freeze
Out description.Comment: 9 pages, 2 figure
Action functionals for relativistic perfect fluids
Action functionals describing relativistic perfect fluids are presented. Two
of these actions apply to fluids whose equations of state are specified by
giving the fluid energy density as a function of particle number density and
entropy per particle. Other actions apply to fluids whose equations of state
are specified in terms of other choices of dependent and independent fluid
variables. Particular cases include actions for isentropic fluids and
pressureless dust. The canonical Hamiltonian forms of these actions are
derived, symmetries and conserved charges are identified, and the boundary
value and initial value problems are discussed. As in previous works on perfect
fluid actions, the action functionals considered here depend on certain
Lagrange multipliers and Lagrangian coordinate fields. Particular attention is
paid to the interpretations of these variables and to their relationships to
the physical properties of the fluid.Comment: 40 pages, plain Te
Identification of genes differentially expressed in T cells following stimulation with the chemokines CXCL12 and CXCL10
BACKGROUND: Chemokines are involved in many biological activities ranging from leukocyte differentiation to neuronal morphogenesis. Despite numerous reports describing chemokine function, little is known about the molecular changes induced by cytokines. METHODS: We have isolated and identified by differential display analysis 182 differentially expressed cDNAs from CXCR3-transfected Jurkat T cells following treatment with CXCL12 or CXCL10. These chemokine-modulated genes were further verified using quantitative RT-PCR and Western blot analysis. RESULTS: One hundred and forty-six of the cDNAs were successfully cloned, sequenced, and identified by BLAST. Following removal of redundant and non-informative clones, seventeen mRNAs were found to be differentially expressed post treatment with either chemokine ligand with several representing known genes with established functions. Twenty-one genes were upregulated in these transfected Jurkat cells following both CXCL12 and CXCL10, four genes displayed a discordant response and seven genes were downregulated upon treatment with either chemokine. Identified genes include geminin (GEM), thioredoxin (TXN), DEAD/H box polypeptide 1 (DDX1), growth hormone inducible transmembrane protein (GHITM), and transcription elongation regulator 1 (TCERG1). Subsequent analysis of several of these genes using semi-quantitative PCR and western blot analysis confirmed their differential expression post ligand treatment. CONCLUSIONS: Together, these results provide insight into chemokine-induced gene activation and identify potentially novel functions for known genes in chemokine biology
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