1,924 research outputs found
Solving the stationary Liouville equation via a boundary element method
Intensity distributions of linear wave fields are, in the high frequency
limit, often approximated in terms of flow or transport equations in phase
space. Common techniques for solving the flow equations for both time dependent
and stationary problems are ray tracing or level set methods. In the context of
predicting the vibro-acoustic response of complex engineering structures,
reduced ray tracing methods such as Statistical Energy Analysis or variants
thereof have found widespread applications. Starting directly from the
stationary Liouville equation, we develop a boundary element method for solving
the transport equations for complex multi-component structures. The method,
which is an improved version of the Dynamical Energy Analysis technique
introduced recently by the authors, interpolates between standard statistical
energy analysis and full ray tracing, containing both of these methods as
limiting cases. We demonstrate that the method can be used to efficiently deal
with complex large scale problems giving good approximations of the energy
distribution when compared to exact solutions of the underlying wave equation
Dynamical energy analysis on mesh grids: a new tool for describing the vibro-acoustic response of complex mechanical structures
We present a new approach for modelling noise and vibration in complex mechanical structures in the mid-to-high frequency regime. It is based on a dynamical energy analysis (DEA) formulation which extends standard techniques such as statistical energy analysis (SEA) towards non-diffusive wave fields. DEA takes into account the full directionality of the wave field and makes sub-structuring obsolete. It can thus be implemented on mesh grids commonly used, for example, in the finite element method (FEM). The resulting mesh based formulation of DEA can be implemented very efficiently using discrete flow mapping (DFM) as detailed in [1] and described here for applications in vibro-acoustics
Flexural properties of fiber reinforced root canal posts.
AbstractOBJECTIVES: Fiber-reinforced
composite (FRC) root canal posts have been introduced to be used
instead of metal alloys and ceramics. The aim of this study was to
investigate the flexural properties of different types of FRC posts and
compare those values with a novel FRC material for dental applications.METHODS: Seventeen
different FRC posts of various brands (Snowpost, Carbopost, Parapost,
C-post, Glassix, Carbonite) and diameters, (1.0-2.1 mm) and a continuous
unidirectional E-glass FRC polymerized by light activation to a
cylindrical form (everStick, diameter 1.5 mm) as a control material were
tested. The posts (n=5) were stored at room's humidity or thermocycled
(12.000 x, 5 degrees C/55 degrees C) and stored in water for 2 weeks
before testing. A three-point bending test (span=10 mm) was used to
measure the flexural strength and modulus of FRC post specimens.RESULTS: Analysis
of ANOVA revealed that thermocycling, brand of material and diameter of
specimen had a significant effect (p<0.001) on the fracture load and
flexural strength. The highest flexural strength was obtained with the
control material (everStick, 1144.9+/-99.9 MPa). There was a linear
relationship between fracture load and diameter of posts for both glass
fiber and carbon fiber posts. Thermocycling decreased the flexural
modulus of the tested specimens by approximately 10%. Strength and
fracture load decreased approximately 18% as a result of thermocycling.SIGNIFICANCE: Considerable
variation can be found in the calculated strength values of the studied
post brands. Commercial prefabricated FRC posts showed lower flexural
properties than an individually polymerised FRC material.</div
The DEAD-box helicase Ded1 from yeast is an mRNP cap-associated protein that shuttles between the cytoplasm and nucleus
International audienceThe DEAD-box helicase Ded1 is an essential yeast protein that is closely related to mammalian DDX3 and to other DEAD-box proteins involved in developmental and cell cycle regulation. Ded1 is considered to be a translation-initiation factor that helps the 40S ribosome scan the mRNA from the 5 7-methylguanosine cap to the AUG start codon. We used IgG pull-down experiments, mass spectrom-etry analyses, genetic experiments, sucrose gradients , in situ localizations and enzymatic assays to show that Ded1 is a cap-associated protein that actively shuttles between the cytoplasm and the nucleus. NanoLC-MS/MS analyses of purified complexes show that Ded1 is present in both nuclear and cytoplasmic mRNPs. Ded1 physically interacts with purified components of the nuclear CBC and the cytoplasmic eIF4F complexes, and its enzymatic activity is stimulated by these factors. In addition, we show that Ded1 is genetically linked to these factors. Ded1 comigrates with these proteins on sucrose gradients, but treatment with rapamycin does not appreciably alter the distribution of Ded1; thus, most of the Ded1 is in stable mRNP complexes. We conclude that Ded1 is an mRNP cofactor of the cap complex that may function to remodel the different mRNPs and thereby regulate the expression of the mRNAs
Nanoscale integration of single cell biologics discovery processes using optofluidic manipulation and monitoring.
The new and rapid advancement in the complexity of biologics drug discovery has been driven by a deeper understanding of biological systems combined with innovative new therapeutic modalities, paving the way to breakthrough therapies for previously intractable diseases. These exciting times in biomedical innovation require the development of novel technologies to facilitate the sophisticated, multifaceted, high-paced workflows necessary to support modern large molecule drug discovery. A high-level aspiration is a true integration of "lab-on-a-chip" methods that vastly miniaturize cellulmical experiments could transform the speed, cost, and success of multiple workstreams in biologics development. Several microscale bioprocess technologies have been established that incrementally address these needs, yet each is inflexibly designed for a very specific process thus limiting an integrated holistic application. A more fully integrated nanoscale approach that incorporates manipulation, culture, analytics, and traceable digital record keeping of thousands of single cells in a relevant nanoenvironment would be a transformative technology capable of keeping pace with today's rapid and complex drug discovery demands. The recent advent of optical manipulation of cells using light-induced electrokinetics with micro- and nanoscale cell culture is poised to revolutionize both fundamental and applied biological research. In this review, we summarize the current state of the art for optical manipulation techniques and discuss emerging biological applications of this technology. In particular, we focus on promising prospects for drug discovery workflows, including antibody discovery, bioassay development, antibody engineering, and cell line development, which are enabled by the automation and industrialization of an integrated optoelectronic single-cell manipulation and culture platform. Continued development of such platforms will be well positioned to overcome many of the challenges currently associated with fragmented, low-throughput bioprocess workflows in biopharma and life science research
Climate effects and stature since 1800
During the last 30 years, economic and social historians have collected and analysed large amounts of anthropometric data in order to explore key aspects of the human past. Attention has also been devoted to the examination of factors that can exert an influence on stature. This article outlines the different ways in which climate might influence stature, either directly or indirectly. It then uses Geographical Information System (GIS) software to explore the relationship between variations in temperature and precipitation and the average heights of men in France, India, Mexico, Spain and the United States (US) over the last two centuries. It is possible to observe an influence of climate on stature in some countries, especially during the nineteenth century, but the relationship weakens across time and largely disappears in recent decades. The attenuation of this relationship is attributed to a process of “technophysio evolution” as countries modernised and developed economically
Variable Infrared Emission from the Supermassive Black Hole at the Center of the Milky Way
We report the detection of a variable point source, imaged at L'(3.8 microns)
with the W. M. Keck II 10-meter telescope's adaptive optics system, that is
coincident to within 18 mas of the Galaxy's central supermassive black hole and
the unique radio source Sgr A*. While in 2002 this source (SgrA*-IR) was
confused with the stellar source S0-2, in 2003 these two sources are separated
by 87 mas allowing the new source's properties to be determined directly. On
four separate nights, its observed L' magnitude ranges from 12.2 to 13.8, which
corresponds to a flux density of 0.7 - 3 mJy, observed, and 4 - 17 mJy,
dereddened; no other source in this region shows such large variations in flux
density - a factor of 4 over a week and a factor of 2 over 40 min. In addition,
it has a K-L' color greater than 2.1, which is at least 1 mag redder than any
other source detected at L' in its vicinity. Based on this source's coincidence
with the Galaxy's dynamical center, its lack of motion, its variability, and
its red color, we conclude that it is associated with the central supermassive
black hole. The short timescale for the 3.8 micron flux density variations
implies that the emission arises in the accretion flow on physical size scales
smaller than 5 AU, or 80 R_s for a 4x10^6 Mo black hole. We suggest that the
3.8 micron emission and the X-ray flares arise from the same underlying
physical process, possibly the acceleration of a small populations of electrons
to ultrarelativistic energies. In contrast to the X-ray flares which are only
detectable 2% of the time, the 3.8 micron emission provides a new, constantly
accessible, window into the physical conditions of the plasma in close
proximity to the central black hole.Comment: published in Astrophysical Journal Letter
A constitutive law for dense granular flows
A continuum description of granular flows would be of considerable help in
predicting natural geophysical hazards or in designing industrial processes.
However, the constitutive equations for dry granular flows, which govern how
the material moves under shear, are still a matter of debate. One difficulty is
that grains can behave like a solid (in a sand pile), a liquid (when poured
from a silo) or a gas (when strongly agitated). For the two extreme regimes,
constitutive equations have been proposed based on kinetic theory for
collisional rapid flows, and soil mechanics for slow plastic flows. However,
the intermediate dense regime, where the granular material flows like a liquid,
still lacks a unified view and has motivated many studies over the past decade.
The main characteristics of granular liquids are: a yield criterion (a critical
shear stress below which flow is not possible) and a complex dependence on
shear rate when flowing. In this sense, granular matter shares similarities
with classical visco-plastic fluids such as Bingham fluids. Here we propose a
new constitutive relation for dense granular flows, inspired by this analogy
and recent numerical and experimental work. We then test our three-dimensional
(3D) model through experiments on granular flows on a pile between rough
sidewalls, in which a complex 3D flow pattern develops. We show that, without
any fitting parameter, the model gives quantitative predictions for the flow
shape and velocity profiles. Our results support the idea that a simple
visco-plastic approach can quantitatively capture granular flow properties, and
could serve as a basic tool for modelling more complex flows in geophysical or
industrial applications.Comment: http://www.nature.com/nature/journal/v441/n7094/abs/nature04801.htm
Planar digital nanoliter dispensing system based on thermocapillary actuation
We provide guidelines for the design and operation of a planar digital nanodispensing system based on
thermocapillary actuation. Thin metallic microheaters embedded within a chemically patterned glass
substrate are electronically activated to generate and control 2D surface temperature distributions
which either arrest or trigger liquid flow and droplet formation on demand. This flow control is
a consequence of the variation of a liquid’s surface tension with temperature, which is used to draw
liquid toward cooler regions of the supporting substrate. A liquid sample consisting of several
microliters is placed on a flat rectangular supply cell defined by chemical patterning. Thermocapillary
switches are then activated to extract a slender fluid filament from the cell and to divide the filament into
an array of droplets whose position and volume are digitally controlled. Experimental results for the
power required to extract a filament and to divide it into two or more droplets as a function of
geometric and operating parameters are in excellent agreement with hydrodynamic simulations. The
capability to dispense ultralow volumes onto a 2D substrate extends the functionality of microfluidic
devices based on thermocapillary actuation previously shown effective in routing and mixing nanoliter
liquid samples on glass or silicon substrates
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