2,021 research outputs found
On Generalized Self-Duality Equations Towards Supersymmetric Quantum Field Theories Of Forms
We classify possible `self-duality' equations for p-form gauge fields in
space-time dimension up to D=16, generalizing the pioneering work of Corrigan
et al. (1982) on Yang-Mills fields (p=1) for D from 5 to 8. We impose two
crucial requirements. First, there should exist a 2(p+1)-form T invariant under
a sub-group H of SO(D). Second, the representation for the SO(D) curvature of
the gauge field must decompose under H in a relevant way. When these criteria
are fulfilled, the `self-duality' equations can be candidates as gauge
functions for SO(D)-covariant and H-invariant topological quantum field
theories. Intriguing possibilities occur for dimensions greater than 9, for
various p-form gauge fields.Comment: 20 pages, Late
Excess Body Weight and Gait Influence Energy Cost of Walking in Older Adults
Purpose: To study how excess body weight influences the energy cost of walking (Cw) and determine if overweight and obese older adults self-select stride frequency to minimize Cw.
Methods: Using body mass index (BMI) men and women between the ages of 65–80 yr were separated into normal weight (NW, BMI ≤ 24.9 kg m−2, n = 13) and overweight-obese groups (OWOB, BMI ≥25.0 kg m−2, n = 13). Subjects walked at 0.83 m s−1 on an instrumented treadmill that recorded gait parameters, and completed three, six-minute walking trials; at preferred stride frequency (PSF), at +10% PSF, and at −10% PSF. Cw was determined by indirect calorimetry. Repeated measures analysis of variance was used to compare groups, and associations were tested with Pearson correlations, α = 0.05.
Results: OWOB had 62% greater absolute Cw (301 ± 108 vs. 186 ± 104 J m−1, P \u3c 0.001) and 20% greater relative Cwkg (3.48 ± 0.95 vs. 2.91 ± 0.94 J kg−1 m−1, P = 0.046) than NW. Although PSF was not different between OWOB and NW (P = 0.626), Cw was 8% greater in OWOB at +10% PSF (P \u3c 0.001). At PSF OWOB spent less time in single-limb support (33.1 ± 1.5 vs. 34.9 ± 1.6 %GC, P = 0.021) and more time in double-limb support (17.5 ± 1.6 vs. 15.4 ± 1.4 %GC, P = 0.026) than NW. In OWOB, at PSF, Cw was correlated to impulse (r = −0.57, P = 0.027) and stride frequency (r = 0.51, P = 0.046).
Conclusions: Excess body weight is associated with greater Cw in older adults, possibly contributing to reduced mobility in overweight and obese older persons
Formation and transportation of sand-heap in an inclined and vertically vibrated container
We report the experimental findings of formation and motion of heap in
granular materials in an inclined and vertically vibrated container. We show
experimentally how the transport velocity of heap up container is related to
the driving acceleration as well as the driving frequency of exciter. An
analogous experiment was performed with a heap-shaped Plexiglas block. We
propose that cohesion force resulted from pressure gradient in ambient gas
plays a crucial role in enhancing and maintaining a heap, and ratchet effect
causes the movement of the heap. An equation which governs the transport
velocity of the heap is presented.Comment: 9 pages, 5 figures, submitted to PR
From sea surface to seafloor: A benthic allochthonous eDNA survey for the abyssal ocean
Environmental DNA (eDNA) metabarcoding could facilitate rapid and comprehensive biotic surveys in the deep ocean, yet many aspects of the sources and distribution of eDNA in the deep sea are still poorly understood. In order to examine the influence of the water column on benthic eDNA surveys in regions targeted for deep-sea polymetallic nodule mining, we investigated the occurrence of pelagic eDNA across: (1) two different deep-sea habitat types, abyssal plains and seamounts, (2) benthic sample types, including nodules, sediment, and seawater within the benthic boundary layer (BBL), and (3) sediment depth horizons (0–2 and 3–5 cm). Little difference was observed between seamounts and the adjacent abyssal plains in the proportion of legacy pelagic eDNA sampled in the benthos, despite >1,000 m depth difference for these habitats. In terms of both reads and amplicon sequence variants (ASVs), pelagic eDNA was minimal within sediment and nodule samples (<2%), and is unlikely to affect benthic surveys that monitor resident organisms at the deep seafloor. However, pelagic eDNA was substantial within the BBL (up to 13% ASVs, 86% reads), derived both from the high-biomass upper ocean as well as deep pelagic residents. While most pelagic metazoan eDNA found in sediments and on nodules could be sourced from the epipelagic, protist legacy eDNA sampled on these substrates appeared to originate across a range of depths in the water column. Some evidence of eDNA degradation across a vertical sediment profile was observed for protists, with higher diversity in the 0–2 cm layer and a significantly lower proportion of legacy pelagic eDNA in deeper sediments (3–5 cm). Study-wide, our estimated metazoan sampling coverage ranged from 40 to 74%, despite relatively large sample size. Future deep-sea eDNA surveys should examine oceanographic influences on eDNA transport and residence times, consider habitat heterogeneity at a range of spatial scales in the abyss, and aim to process large amounts of material per sample (with replication) in order to increase the sampling coverage in these diverse deep ocean communities.publishedVersio
Influence of metallic nanoparticles on upconversion processes
It is well known that Raman scattering and fluorescence can be enhanced by
the presence of metallic nanoparticles. Here, we derive simple equations to
analyse the influence of metallic nanoparticles on upconversion processes such
as non-radiative energy transfer or excited state absorption. We compare the
resulting expressions with the more familiar Raman and fluorescence cases, and
find significant differences. We use numerical simulations to calculate the
upconverted signal enhancement achievable by means of metallic spheres of
different radii, and find particles of 100-400nm radius at infrared frequencies
to be favorable. We also discuss the considerable challenges involved in using
metallic particles to enhance upconversion for solar energy.Comment: Changes mostly made on the structure of the text and on the notation
to improve clarity. Other changes attempt to better clarify the conditions
under which the equations and simulations are valid. Main results and
conclusions essentially unchange
Heterogeneous Extractive Batch Distillation of Chloroform - Methanol – Water : Feasibility and Experiments
A novel heterogeneous extractive distillation process is considered for separating the azeotropic mixture chloroform – methanol in a batch rectifying column, including for the first time an experimental validation of the process. Heterogeneous heavy entrainer water is selected inducing an unstable ternary heteroazeotrope and a saddle binary heteroazeotrope with chloroform (ternary diagram class 2.1-2b). Unlike to well-known heterogeneous azeotropic distillation process and thanks to continuous water feeding at the column top, the saddle binary heteroazeotrope chloroform – water is obtained at the column top, condensed and further split into the liquid – liquid decanter where the chloroform-rich phase is drawn as distillate. First, feasibility analysis is carried out by using a simplified differential model in the extractive section for determining the proper range of the entrainer flowrate and the reflux ratio. The operating conditions and reflux policy are validated by rigorous simulation with ProSim Batch Column® where technical features of a bench scale distillation column have been described. Six reproducible experiments are run in the bench scale column matching the simulated operating conditions with two sequentially increasing reflux ratio values. Simulation and experiments agree well. With an average molar purity higher than 99%, more than 85% of recovery yield was obtained for chloroform and methanol
Photochemical Chemoselective Alkylation of Tryptophan-Containing Peptides
We report a photochemical method for the chemoselective radical functionalization of tryptophan (Trp)-containing peptides. The method exploits the photoactivity of an electron donor-acceptor complex generated between the tryptophan unit and pyridinium salts. Irradiation with weak light (390 nm) generates radical intermediates right next to the targeted Trp amino acid, facilitating a proximity-driven radical functionalization. This protocol exhibits high chemoselectivity for Trp residues over other amino acids and tolerates biocompatible conditions
Experimental study and numerical simulation of preform or sheet exposed to infrared radiative heating
International conference on Advances in Materials and Processing Technology, DUBLIN, IRELAND, AUG 03-06, 1999International audienceThermoplastic processing like the injection stretch blow moulding and thermoforming processes provide the heating stage with infrared oven. This is a critical stage of the process, as the final part thickness is strongly dependent on the preform or sheet temperature distribution prior to forming. Optimisation of the infrared oven is therefore necessary. Experiments have been conducted in order to characterise the heat source of the infrared emitter and the interaction between the heaters and a semi-transparent PET sheet. An 880 LW AGEMA infrared camera has been used to determine the surface distribution of the transmitted heat flux by measuring the temperature distribution on the surface of the thermoplastic sheet. In addition, numerical simulations of the temperature distribution using control-volume method have been carried out and compared with experimental data
Fluctuation-Dissipation-Theorem violation during the formation of a colloidal-glass
The relationship between the conductivity and the polarization noise is
measured in a gel as a function of frequency in the range . It is
found that at the beginning of the transition from a fluid like sol to a solid
like gel the fluctuation dissipation theorem is strongly violated. The
amplitude and the persistence time of this violation are decreasing functions
of frequency. At the lowest frequencies of the measuring range it persists for
times which are about 5% of the time needed to form the gel. This phenomenology
is quite close to the recent theoretical predictions done for the violation of
the fluctuation dissipation theorem in glassy systems.Comment: 6 pages + 4 figure
Intracerebral Implantation of Hydrogel-Coupled Adhesion Peptides: Tissue Reaction
Arg-Gly-Asp peptides (RGD) were synthesized
and chemically coupled to the bulk of N-(2-hydroxypropyl) methacrylamide-based polymer
hydrogels. Fourier Transform Infrared Spectroscopy
(FFIR) and amino acid analysis confirmed
the peptide coupling to the polymer. Activated
and control (unmodified) polymer matrices were
stereotaxically implanted in the striata of rat
brains, and two months later the brains were
processed for immunohistochemistry using antibodies
for glial acidic fibrillary protein (GFAP),
laminin and neurofilaments. RGD-containing
polymer matrices promoted stronger adhesion to
the host tissue than the unmodified polymer
matrices. In addition, the RGD-grafted polymer
implants promoted and supported the growth
and spread of GFAP-positive glial tissue onto
and into the hydrogels. Neurofilament-positive
fibers were also seen running along the surface
of the polymer and, in some instances, penetrating
the matrix. These findings are discussed
in the context of using bioactive polymers as a
new approach for promoting tissue repair and
axonal regeneration of damaged structures of
the central nervous system
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