142 research outputs found
Averaging rheological quantities in descriptions of soft glassy materials
Many mean-field models have been introduced to describe the mechanical
behavior of glassy materials. They often rely on averages performed over
distributions of elements or states. We here underline that averaging is a more
intricate procedure in mechanics than in more classical situations such as
phase transitions in magnetic systems. This leads us to modify the predictions
of the recently proposed SGR model for soft glassy materials, for which we
suggest that the viscosity should diverge at the glass transition temperature
with an exponential form .Comment: 4 pages, Latex, 1 eps figur
Capillary micromechanics: Measuring the elasticity of microscopic soft objects
We present a simple method for accessing the elastic properties of
microscopic deformable particles. This method is based on measuring the
pressure-induced deformation of soft particles as they are forced through a
tapered glass microcapillary. It allows us to determine both the compressive
and the shear modulus of a deformable object in one single experiment.
Measurements on a model system of poly-acrylamide microgel particles exhibit
excellent agreement with measurements on bulk gels of identical composition.
Our approach is applicable over a wide range of mechanical properties and
should thus be a valuable tool for the characterization of a variety of soft
and biological materials
Old Goucher neighborhood : strengthening a community identity through an exploration of the past
"University of Maryland School of Architecture, Planning & Preservation, Graduate Program in Historic Preservation, Fall 2013.
Rheological constitutive equation for model of soft glassy materials
We solve exactly and describe in detail a simplified scalar model for the low
frequency shear rheology of foams, emulsions, slurries, etc. [P. Sollich, F.
Lequeux, P. Hebraud, M.E. Cates, Phys. Rev. Lett. 78, 2020 (1997)]. The model
attributes similarities in the rheology of such ``soft glassy materials'' to
the shared features of structural disorder and metastability. By focusing on
the dynamics of mesoscopic elements, it retains a generic character.
Interactions are represented by a mean-field noise temperature x, with a glass
transition occurring at x=1 (in appropriate units). The exact solution of the
model takes the form of a constitutive equation relating stress to strain
history, from which all rheological properties can be derived. For the linear
response, we find that both the storage modulus G' and the loss modulus G''
vary with frequency as \omega^{x-1} for 1<x<2, becoming flat near the glass
transition. In the glass phase, aging of the moduli is predicted. The steady
shear flow curves show power law fluid behavior for x<2, with a nonzero yield
stress in the glass phase; the Cox-Merz rule does not hold in this
non-Newtonian regime. Single and double step strains further probe the
nonlinear behavior of the model, which is not well represented by the BKZ
relation. Finally, we consider measurements of G' and G'' at finite strain
amplitude \gamma. Near the glass transition, G'' exhibits a maximum as \gamma
is increased in a strain sweep. Its value can be strongly overestimated due to
nonlinear effects, which can be present even when the stress response is very
nearly harmonic. The largest strain \gamma_c at which measurements still probe
the linear response is predicted to be roughly frequency-independent.Comment: 24 pages, REVTeX, uses multicol, epsf and amssymp; 20 postscript
figures (included). Minor changes to text (relation to mode coupling theory,
update on recent foam simulations etc.) and figures (emphasis on low
frequency regime); typos corrected and reference added. Version to appear in
Physical Review
Rapid Assessment of Power Requirements and Optimization of Thermal Ice Protection Systems
Presented at 2018 Aviation Technology, Integration, and Operations Conference (AIAA 2018-4136)A thermal ice protection system prevents or dispatches ice formed on critical aircraft components like wings or nacelles by heating them either through electro-thermal or pneumatic means. The power requirements for such a system are a function of flight and atmospheric conditions and protected surface area. The developed analysis framework allows evaluation of transient and steady-state cases, anti-icing and de-icing designs, as well as evaporative and running-wet operation. To enable these analyses, a flow solver is first used to calculate local water catch efficiencies and convective heat transfer coefficients on an airfoil. These are then used within a thermal solver which evaluates water and ice accumulations over multiple control volumes under different cases of interest. This control volume approach includes both thermal and mass balances to track temperatures of the protected surface, ice, and water, as well as water/ice layer thicknesses and the water mass flow in or out of the control volume through evaporation or runback. Finally, this tool can yield power requirements for different system layouts and operating conditions, or optimize the protected surface area for a given airfoil under given operating conditions. This can help designers get an estimate of the power draw, and obtain more information on placement of the IPS on novel configurations during the design space exploration phase itself with greater fidelity and minimal computational costs
The Temporal Signature of Memories: Identification of a General Mechanism for Dynamic Memory Replay in Humans
Reinstatement of dynamic memories requires the replay of neural patterns that unfold over
time in a similar manner as during perception. However, little is known about the mechanisms
that guide such a temporally structured replay in humans, because previous studies
used either unsuitable methods or paradigms to address this question. Here, we overcome
these limitations by developing a new analysis method to detect the replay of temporal patterns
in a paradigm that requires participants to mentally replay short sound or video clips.
We show that memory reinstatement is accompanied by a decrease of low-frequency (8
Hz) power, which carries a temporal phase signature of the replayed stimulus. These replay
effects were evident in the visual as well as in the auditory domain and were localized to
sensory-specific regions. These results suggest low-frequency phase to be a domain-general
mechanism that orchestrates dynamic memory replay in humans
Phenytoin versus Leviteracetam for seizure prophylaxis after brain injury - A meta analysis
Background: Current standard therapy for seizure prophylaxis in Neuro-surgical patients involves the use of Phenytoin (PHY). However, a new drug Levetiracetam (LEV) is emerging as an alternate treatment choice. We aimed to conduct a meta-analysis to compare these two drugs in patients with brain injury.Methods: An electronic search was performed in using Pubmed, Embase, and CENTRAL. We included studies that compared the use of LEV vs. PHY for seizure prophylaxis for brain injured patients (Traumatic brain injury, intracranial hemorrhage, intracranial neoplasms, and craniotomy). Data of all eligible studies was extracted on to a standardized abstraction sheet. Data about baseline population characteristics, type of intervention, study design and outcome was extracted. Our primary outcome was seizures.Results: The literature search identified 2489 unduplicated papers. Of these 2456 papers were excluded by reading the abstracts and titles. Another 25 papers were excluded after reading their complete text. We selected 8 papers which comprised of 2 RCTs and 6 observational studies. The pooled estimate\u27s Odds Ratio 1.12 (95% CI = 0.34, 3.64) demonstrated no superiority of either drug at preventing the occurrence of early seizures. In a subset analysis of studies in which follow up for seizures lasted either 3 or 7 days, the effect estimate remained insignificant with an odds ratio of 0.96 (95% CI = 0.34, 2.76). Similarly, 2 trials reporting seizure incidence at 6 months also had insignificant pooled results while comparing drug efficacy. The pooled odds ratio was 0.96 (95% CI = 0.24, 3.79).Conclusions: Levetiracetam and Phenytoin demonstrate equal efficacy in seizure prevention after brain injury. However, very few randomized controlled trials (RCTs) on the subject were found. Further evidence through a high quality RCT is highly recommended
A review of the renal system and diurnal variations of renal activity in livestock
Kidneys are the main organs regulating water-electrolyte homeostasis in the body. They are responsible for maintaining the total volume of water and its distribution in particular water spaces, for electrolyte composition of systemic fluids and also for maintaining acid-base balance. These functions are performed by the plasma filtration process in renal glomeruli and the processes of active absorption and secretion in renal tubules, all adjusted to an 'activity-rest' rhythm. These diurnal changes are influenced by a 24-hour cycle of activity of hormones engaged in the regulation of renal activity. Studies on spontaneous rhythms of renal activity have been carried out mainly on humans and laboratory animals, but few studies have been carried out on livestock animals. Moreover, those results cover only some aspects of renal physiology. This review gives an overview of current knowledge concerning renal function and diurnal variations of some renal activity parameters in livestock, providing greater understanding of general chronobiological processes in mammals. Detailed knowledge of these rhythms is useful for clinical, practical and pharmacological purposes, as well as studies on their physical performance
A Domain-Agnostic Approach for Characterization of Lifelong Learning Systems
Despite the advancement of machine learning techniques in recent years,
state-of-the-art systems lack robustness to "real world" events, where the
input distributions and tasks encountered by the deployed systems will not be
limited to the original training context, and systems will instead need to
adapt to novel distributions and tasks while deployed. This critical gap may be
addressed through the development of "Lifelong Learning" systems that are
capable of 1) Continuous Learning, 2) Transfer and Adaptation, and 3)
Scalability. Unfortunately, efforts to improve these capabilities are typically
treated as distinct areas of research that are assessed independently, without
regard to the impact of each separate capability on other aspects of the
system. We instead propose a holistic approach, using a suite of metrics and an
evaluation framework to assess Lifelong Learning in a principled way that is
agnostic to specific domains or system techniques. Through five case studies,
we show that this suite of metrics can inform the development of varied and
complex Lifelong Learning systems. We highlight how the proposed suite of
metrics quantifies performance trade-offs present during Lifelong Learning
system development - both the widely discussed Stability-Plasticity dilemma and
the newly proposed relationship between Sample Efficient and Robust Learning.
Further, we make recommendations for the formulation and use of metrics to
guide the continuing development of Lifelong Learning systems and assess their
progress in the future.Comment: To appear in Neural Network
Catálogo de autoridades da Rede BIM (DPHDM): Estudo de caso no tratamento de registros de pontos de acesso
Identificar possíveis problemas na alimentação da base de autoridades de assuntos da Rede BIM através da utilização do software Pergamum, e contribuir para padronização de seus pontos de acesso. A partir da revisão da literatura proposta, considera a importância da recuperação da informação para sua disseminação e ainda faz um breve levantamento dos padrões internacionais utilizados para esse fim. A metodologia utilizada envolveu a análise da base, limitada à letra “c” do alfabeto, e se propôs a detectar possíveis inconsistências existentes. Os principais problemas encontrados foram: falhas de grafia, falhas de entrada de cabeçalhos e duplicidade de assuntos. Os resultados práticos para a Rede BIM são: agilização dos serviços de catalogação e referência da Rede BIM, maior controle bibliográfico e facilidade na recuperação de itens nas pesquisas dos usuários. O Estudo de caso se propõe a contribuir com esclarecimentos quanto a equívocos cometidos, de forma a auxiliar na padronização e documentação do processo de alimentação da base de autoridades de assuntos pelos bibliotecários das 45 organizações militares, possibilitando benefícios aos serviços de catalogação e referência e finalmente, propiciando um atendimento mais prático e ágil ao usuário da Rede BIM
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