380 research outputs found
Phonons and thermal transport in Si/SiO multishell nanotubes: Atomistic study
Thermal transport in the Si/SiO multishell nanotubes is investigated
theoretically. The phonon energy spectra are obtained using the atomistic
Lattice Dynamics approach. Thermal conductivity is calculated using the
Boltzmann transport equation within the relaxation time approximation.
Redistribution of the vibrational spectra in multishell nanotubes leads to a
decrease of the phonon group velocity and the thermal conductivity as compared
to homogeneous Si nanowires. Phonon scattering on the Si/SiO interfaces is
another key factor of strong reduction of the thermal conductivity in these
structures (down to 0.2 W/mK at room temperature). We demonstrate that phonon
thermal transport in Si/SiO nanotubes can be efficiently suppressed by a
proper choice of nanotube's geometrical parameters: lateral cross-section,
thickness and number of shells.Comment: 14 pages, 4 figure
Adipose Tissue as a Site of Toxin Accumulation
We examine the role of adipose tissue, typically considered an energy storage site, as a potential site of toxicant accumulation. Although the production of most persistent organic pollutants (POPs) was banned years ago, these toxicants persist in the environment due to their resistance to biodegradation and widespread distribution in various environmental forms (e.g., vapor, sediment, and water). As a result, human exposure to these toxicants is inevitable. Largely due to their lipophilicity, POPs bioaccumulate in adipose tissue, resulting in greater body burdens of these environmental toxicants with obesity. POPs of major concern include polychlorinated biphenyls (PCBs), polychlorinated dibenzoβpβdioxins and furans (PCDDs/PCDFs), and polybrominated biphenyls and diphenyl ethers (PBBs/PBDEs), among other organic compounds. In this review, we 1) highlight the physical characteristics of toxicants that enable them to partition into and remain stored in adipose tissue, 2) discuss the specific mechanisms of action by which these toxicants act to influence adipocyte function, and 3) review associations between POP exposures and the development of obesity and diabetes. An area of controversy relates to the relative potential beneficial versus hazardous health effects of toxicant sequestration in adipose tissue
Modeling Genomes to Phenomes to Populations in a Changing Climate: The Need for Collaborative Networks
Condensed Abstract
Climate is changing globally and its impacts can arise at different levels of biological organization; yet, cross-level consequences of climate change are still poorly understood. Designing effective environmental management and adaptation plans requires implementation of mechanistic models that span the biological hierarchy. Because biological systems are inherently complex and dynamic in nature, dealing with complexities efficiently necessitates simplification of systems or approximation of relevant processes, but there is little consensus on mathematical approaches to scale from genes to populations. Here we present an effort that aims to bring together groups that often do not interact, but that are essential to illuminating the complexities of life: empirical scientists and mathematical modelers, spanning levels of biological organization from genomes to organisms to populations. Through interplay between theory, models, and data, we aim to facilitate the generation of a new synthesis and a conceptual framework for biology across levels
Association of Pediatric Heart Transplant Coronary Vasculopathy with Abnormal Hemodynamic Measures
Objective.β Transplant coronary artery disease (TCAD) is the limiting factor to longβterm cardiac allograft survival; however, presymptomatic diagnosis remains challenging. To that concern, we evaluated the association of abnormal catheterβderived filling pressures with TCAD in pediatric heart transplant (HTx) recipients.Design, Patients, Outcome Measures.β Data from 52 presymptomatic pediatric HTx patients were analyzed. Catheterβderived right ventricular endβdiastolic pressure (RVEDP) and pulmonary capillary wedge pressure (PCWP) were recorded. Biopsies were collected to verify the absence of rejection.Results.β TCAD was diagnosed an average of 8.3 years postβHTx in 20 (38%) patients, six of whom died and four of whom underwent retransplantation. Catheterβderived pressure measurements showed that RVEDP was elevated in TCAD compared with nonβTCAD patients (9.5 Β± 6.0 vs. 5.4 Β± 4.7; P= .005), as was the PCWP (12.9 Β± 5.7 vs. 9.1 Β± 5.7; P= .012). Results from logistic regression analysis showed RVEDP > 10βmmβHg or PCWP > 12βmmβHg was associated with TCAD (OR = 5.2; P= .010).Conclusions.β In this series, elevated ventricular filling pressures measured during routine surveillance catheterizations were associated with angiographic TCAD. Recognizing the association between elevated RVEDP/PCWP and TCAD may prompt earlier diagnosis and treatment of this potentially lethal process.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111940/1/j.1747-0803.2010.00470.x.pd
Gene expression profiling suggests that complement activation is important for blister formation in bullous pemphigoid
Probing Mechanical Properties of Graphene with Raman Spectroscopy
The use of Raman scattering techniques to study the mechanical properties of
graphene films is reviewed here. The determination of Gruneisen parameters of
suspended graphene sheets under uni- and bi-axial strain is discussed and the
values are compared to theoretical predictions. The effects of the
graphene-substrate interaction on strain and to the temperature evolution of
the graphene Raman spectra are discussed. Finally, the relation between
mechanical and thermal properties is presented along with the characterization
of thermal properties of graphene with Raman spectroscopy.Comment: To appear in the Journal of Materials Scienc
A gp41 MPER-specific llama VHH requires a hydrophobic CDR3 for neutralization but not for antigen recognition
The membrane proximal external region (MPER) of the HIV-1 glycoprotein gp41 is targeted by the broadly neutralizing antibodies 2F5 and 4E10. To date, no immunization regimen in animals or humans has produced HIV-1 neutralizing MPER-specific antibodies. We immunized llamas with gp41-MPER proteoliposomes and selected a MPER-specific single chain antibody (VHH), 2H10, whose epitope overlaps with that of mAb 2F5. Bi-2H10, a bivalent form of 2H10, which displayed an approximately 20-fold increased affinity compared to the monovalent 2H10, neutralized various sensitive and resistant HIV-1 strains, as well as SHIV strains in TZM-bl cells. X-ray and NMR analyses combined with mutagenesis and modeling revealed that 2H10 recognizes its gp41 epitope in a helical conformation. Notably, tryptophan 100 at the tip of the long CDR3 is not required for gp41 interaction but essential for neutralization. Thus bi-2H10 is an anti-MPER antibody generated by immunization that requires hydrophobic CDR3 determinants in addition to epitope recognition for neutralization similar to the mode of neutralization employed by mAbs 2F5 and 4E10
Thermal Conductivity and Thermal Rectification in Graphene Nanoribbons: a Molecular Dynamics Study
We have used molecular dynamics to calculate the thermal conductivity of
symmetric and asymmetric graphene nanoribbons (GNRs) of several nanometers in
size (up to ~4 nm wide and ~10 nm long). For symmetric nanoribbons, the
calculated thermal conductivity (e.g. ~2000 W/m-K @400K for a 1.5 nm {\times}
5.7 nm zigzag GNR) is on the similar order of magnitude of the experimentally
measured value for graphene. We have investigated the effects of edge chirality
and found that nanoribbons with zigzag edges have appreciably larger thermal
conductivity than nanoribbons with armchair edges. For asymmetric nanoribbons,
we have found significant thermal rectification. Among various
triangularly-shaped GNRs we investigated, the GNR with armchair bottom edge and
a vertex angle of 30{\deg} gives the maximal thermal rectification. We also
studied the effect of defects and found that vacancies and edge roughness in
the nanoribbons can significantly decrease the thermal conductivity. However,
substantial thermal rectification is observed even in the presence of edge
roughness.Comment: 13 pages, 5 figures, slightly expanded from the published version on
Nano Lett. with some additional note
Simulation of heat transport in low-dimensional oscillator lattices
The study of heat transport in low-dimensional oscillator lattices presents a
formidable challenge. Theoretical efforts have been made trying to reveal the
underlying mechanism of diversified heat transport behaviors. In lack of a
unified rigorous treatment, approximate theories often may embody controversial
predictions. It is therefore of ultimate importance that one can rely on
numerical simulations in the investigation of heat transfer processes in
low-dimensional lattices. The simulation of heat transport using the
non-equilibrium heat bath method and the Green-Kubo method will be introduced.
It is found that one-dimensional (1D), two-dimensional (2D) and
three-dimensional (3D) momentum-conserving nonlinear lattices display power-law
divergent, logarithmic divergent and constant thermal conductivities,
respectively. Next, a novel diffusion method is also introduced. The heat
diffusion theory connects the energy diffusion and heat conduction in a
straightforward manner. This enables one to use the diffusion method to
investigate the objective of heat transport. In addition, it contains
fundamental information about the heat transport process which cannot readily
be gathered otherwise.Comment: Article published in: Thermal transport in low dimensions: From
statistical physics to nanoscale heat transfer, S. Lepri, ed. Lecture Notes
in Physics, vol. 921, pp. 239 - 274, Springer-Verlag, Berlin, Heidelberg, New
York (2016
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