1,552 research outputs found
A Simple Boltzmann Transport Equation for Ballistic to Diffusive Transient Heat Transport
Developing simplified, but accurate, theoretical approaches to treat heat
transport on all length and time scales is needed to further enable scientific
insight and technology innovation. Using a simplified form of the Boltzmann
transport equation (BTE), originally developed for electron transport, we
demonstrate how ballistic phonon effects and finite-velocity propagation are
easily and naturally captured. We show how this approach compares well to the
phonon BTE, and readily handles a full phonon dispersion and energy-dependent
mean-free-path. This study of transient heat transport shows i) how fundamental
temperature jumps at the contacts depend simply on the ballistic thermal
resistance, ii) that phonon transport at early times approach the ballistic
limit in samples of any length, and iii) perceived reductions in heat
conduction, when ballistic effects are present, originate from reductions in
temperature gradient. Importantly, this framework can be recast exactly as the
Cattaneo and hyperbolic heat equations, and we discuss how the key to capturing
ballistic heat effects is to use the correct physical boundary conditions.Comment: 9 pages, 5 figure
Content-based microarray search using differential expression profiles
<p>Abstract</p> <p>Background</p> <p>With the expansion of public repositories such as the Gene Expression Omnibus (GEO), we are rapidly cataloging cellular transcriptional responses to diverse experimental conditions. Methods that query these repositories based on gene expression content, rather than textual annotations, may enable more effective experiment retrieval as well as the discovery of novel associations between drugs, diseases, and other perturbations.</p> <p>Results</p> <p>We develop methods to retrieve gene expression experiments that differentially express the same transcriptional programs as a query experiment. Avoiding thresholds, we generate differential expression profiles that include a score for each gene measured in an experiment. We use existing and novel dimension reduction and correlation measures to rank relevant experiments in an entirely data-driven manner, allowing emergent features of the data to drive the results. A combination of matrix decomposition and <it>p</it>-weighted Pearson correlation proves the most suitable for comparing differential expression profiles. We apply this method to index all GEO DataSets, and demonstrate the utility of our approach by identifying pathways and conditions relevant to transcription factors Nanog and FoxO3.</p> <p>Conclusions</p> <p>Content-based gene expression search generates relevant hypotheses for biological inquiry. Experiments across platforms, tissue types, and protocols inform the analysis of new datasets.</p
Recycling of Pretreated Polyolefin-Based Ocean-Bound Plastic Waste by Incorporating Clay and Rubber
Plastic waste found in oceans has become a major concern because of its impact on marine organisms and human health. There is significant global interest in recycling these materials, but their reclamation, sorting, cleaning, and reprocessing, along with the degradation that occurs in the natural environment, all make it difficult to achieve high quality recycled resins from ocean plastic waste. To mitigate these limitations, various additives including clay and rubber were explored. In this study, we compounded different types of ocean-bound (o-HDPE and o-PP) and virgin polymers (v-LDPE and v-PS) with various additives including a functionalized clay, styrene-multi-block-copolymer (SMB), and ethylene-propylene-based rubber (EPR). Physical observation showed that all blends containing PS were brittle due to the weak interfaces between the polyolefin regions and the PS domains within the polymer blend matrix. Blends containing clay showed rough surfaces and brittleness because of the non-uniform distribution of clay particles in the polymer matrix. To evaluate the properties and compatibility of the blends, characterizations using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and small-amplitude oscillatory shear (SAOS) rheology were carried out. The polymer blend (v-LDPE, o-HDPE, o-PP) containing EPR showed improved elasticity. Incorporating additives such as rubber could improve the mechanical properties of polymer blends for recycling purposes
An Analytic Variational Study of the Mass Spectrum in 2+1 Dimensional SU(3) Hamiltonian Lattice Gauge Theory
We calculate the masses of the lowest lying eigenstates of improved SU(2) and
SU(3) lattice gauge theory in 2+1 dimensions using an analytic variational
approach. The ground state is approximated by a one plaquette trial state and
mass gaps are calculated in the symmetric and antisymmetric sectors by
minimising over a suitable basis of rectangular states
Identifying Boosted Objects with N-subjettiness
We introduce a new jet shape -- N-subjettiness -- designed to identify
boosted hadronically-decaying objects like electroweak bosons and top quarks.
Combined with a jet invariant mass cut, N-subjettiness is an effective
discriminating variable for tagging boosted objects and rejecting the
background of QCD jets with large invariant mass. In efficiency studies of
boosted W bosons and top quarks, we find tagging efficiencies of 30% are
achievable with fake rates of 1%. We also consider the discovery potential for
new heavy resonances that decay to pairs of boosted objects, and find
significant improvements are possible using N-subjettiness. In this way,
N-subjettiness combines the advantages of jet shapes with the discriminating
power seen in previous jet substructure algorithms.Comment: 26 pages, 26 figures, 2 tables; v2: references added; v3: discussion
of results extende
Tetrahedral colloidal clusters from random parking of bidisperse spheres
Using experiments and simulations, we investigate the clusters that form when
colloidal spheres stick irreversibly to -- or "park" on -- smaller spheres. We
use either oppositely charged particles or particles labeled with complementary
DNA sequences, and we vary the ratio of large to small sphere radii.
Once bound, the large spheres cannot rearrange, and thus the clusters do not
form dense or symmetric packings. Nevertheless, this stochastic aggregation
process yields a remarkably narrow distribution of clusters with nearly 90%
tetrahedra at . The high yield of tetrahedra, which reaches 100%
in simulations at , arises not simply because of packing
constraints, but also because of the existence of a long-time lower bound that
we call the "minimum parking" number. We derive this lower bound from solutions
to the classic mathematical problem of spherical covering, and we show that
there is a critical size ratio , close to
the observed point of maximum yield, where the lower bound equals the upper
bound set by packing constraints. The emergence of a critical value in a random
aggregation process offers a robust method to assemble uniform clusters for a
variety of applications, including metamaterials.Comment: 24 pages, 6 figure
GluN2A NMDA Receptor Enhancement Improves Brain Oscillations, Synchrony, and Cognitive Functions in Dravet Syndrome and Alzheimer's Disease Models.
NMDA receptors (NMDARs) play subunit-specific roles in synaptic function and are implicated in neuropsychiatric and neurodegenerative disorders. However, the in vivo consequences and therapeutic potential of pharmacologically enhancing NMDAR function via allosteric modulation are largely unknown. We examine the in vivo effects of GNE-0723, a positive allosteric modulator of GluN2A-subunit-containing NMDARs, on brain network and cognitive functions in mouse models of Dravet syndrome (DS) and Alzheimer's disease (AD). GNE-0723 use dependently potentiates synaptic NMDA receptor currents and reduces brain oscillation power with a predominant effect on low-frequency (12-20 Hz) oscillations. Interestingly, DS and AD mouse models display aberrant low-frequency oscillatory power that is tightly correlated with network hypersynchrony. GNE-0723 treatment reduces aberrant low-frequency oscillations and epileptiform discharges and improves cognitive functions in DS and AD mouse models. GluN2A-subunit-containing NMDAR enhancers may have therapeutic benefits in brain disorders with network hypersynchrony and cognitive impairments
Photo-induced second-order nonlinearity in stoichiometric silicon nitride waveguides
We report the observation of second-harmonic generation in stoichiometric
silicon nitride waveguides grown via low-pressure chemical vapour deposition.
Quasi-rectangular waveguides with a large cross section were used, with a
height of 1 {\mu}m and various different widths, from 0.6 to 1.2 {\mu}m, and
with various lengths from 22 to 74 mm. Using a mode-locked laser delivering
6-ps pulses at 1064 nm wavelength with a repetition rate of 20 MHz, 15% of the
incoming power was coupled through the waveguide, making maximum average powers
of up to 15 mW available in the waveguide. Second-harmonic output was observed
with a delay of minutes to several hours after the initial turn-on of pump
radiation, showing a fast growth rate between 10 to 10 s,
with the shortest delay and highest growth rate at the highest input power.
After this first, initial build-up, the second-harmonic became generated
instantly with each new turn-on of the pump laser power. Phase matching was
found to be present independent of the used waveguide width, although the
latter changes the fundamental and second-harmonic phase velocities. We address
the presence of a second-order nonlinearity and phase matching, involving an
initial, power-dependent build-up, to the coherent photogalvanic effect. The
effect, via the third-order nonlinearity and multiphoton absorption leads to a
spatially patterned charge separation, which generates a spatially periodic,
semi-permanent, DC-field-induced second-order susceptibility with a period that
is appropriate for quasi-phase matching. The maximum measured second-harmonic
conversion efficiency amounts to 0.4% in a waveguide with 0.9 x 1 {\mu}m
cross section and 36 mm length, corresponding to 53 {\mu}W at 532 nm with 13 mW
of IR input coupled into the waveguide. The according amounts to
3.7 pm/V, as retrieved from the measured conversion efficiency.Comment: 20 pages, 10 figure
Watching Domains Grow: In-situ studies of polarization switching by combined Scanning Probe and Scanning Transmission Electron Microscopy
Ferroelectric domain nucleation and growth in multiferroic BiFeO3 films is
observed directly by applying a local electric field with a conductive tip
inside a scanning transmission electron microscope. The nucleation and growth
of a ferroelastic domain and its interaction with pre-existing 71^{\circ}
domain walls are observed and compared with the results of phase-field
modeling. In particular, a preferential nucleation site and direction-dependent
pinning of domain walls is observed due to slow kinetics of metastable
switching in the sample without a bottom electrode. These in-situ
spatially-resolved observations of a first-order bias-induced phase transition
reveal the mesoscopic mechanisms underpinning functionality of a wide range of
multiferroic materials
Insulin resistance and chronic kidney disease progression, cardiovascular events, and death: findings from the chronic renal insufficiency cohort study
Abstract
Background
Insulin resistance contributes to the metabolic syndrome, which is associated with the development of kidney disease. However, it is unclear if insulin resistance independently contributes to an increased risk of chronic kidney disease (CKD) progression or CKD complications. Additionally, predisposing factors responsible for insulin resistance in the absence of diabetes in CKD are not well described. This study aimed to describe factors associated with insulin resistance and characterize the relationship of insulin resistance to CKD progression, cardiovascular events and death among a cohort of non-diabetics with CKD.
Methods
Data was utilized from Chronic Renal Insufficiency Cohort Study participants without diabetes (N = 1883). Linear regression was used to assess associations with insulin resistance, defined using the Homeostasis Model Assessment of Insulin Resistance (HOMA-IR). The relationship of HOMA-IR, fasting glucose, hemoglobin A1c (HbA1c), and C-peptide with CKD progression, cardiovascular events, and all-cause mortality was examined with Cox proportional hazards models.
Results
Novel positive associations with HOMA-IR included serum albumin, uric acid, and hemoglobin A1c. After adjustment, HOMA-IR was not associated with CKD progression, cardiovascular events, or all-cause mortality. There was a notable positive association of one standard deviation increase in HbA1c with the cardiovascular endpoint (HR 1.16, 95% CI: 1.00–1.34).
Conclusion
We describe potential determinants of HOMA-IR among a cohort of non-diabetics with mild-moderate CKD. HOMA-IR was not associated with renal or cardiovascular events, or all-cause mortality, which adds to the growing literature describing an inconsistent relationship of insulin resistance with CKD-related outcomes.https://deepblue.lib.umich.edu/bitstream/2027.42/148132/1/12882_2019_Article_1220.pd
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