11,949 research outputs found
Comparison of Material Properties and Microstructure of Specimens Built Using the 3D Systems Vanguard HS and Vanguard HiQ+HSSLS Systems
The HiQ upgrade to the 3D Systems Vanguard selective laser sintering (SLS) machine incorporates a revised thermal calibration system and new control software. The paper compares
the tensile modulus, tensile strength, elongation at break, flexural modulus, Izod impact resistance and microstructure of two batteries of standard specimens built from recycled Duraform
PA (Nylon 12). The first set is built on a Vanguard HS system and the second on the same
system with the HiQ upgrade installed. The upgrade reduces user intervention, decreases total build time and improves surface finish. However, using the default processing parameters,
tensile, flexure and impact properties are all found to decline after the upgrade is installed.Mechanical Engineerin
Chiral molecules split light: Reflection and refraction in a chiral liquid
A light beam changes direction as it enters a liquid at an angle from another
medium, such as air. Should the liquid contain molecules that lack mirror
symmetry, then it has been predicted by Fresnel that the light beam will not
only change direction, but will actually split into two separate beams with a
small difference in the respective angles of refraction. Here we report the
observation of this phenomenon. We also demonstrate that the angle of
reflection does not equal the angle of incidence in a chiral medium. Unlike
conventional optical rotation, which depends on the path-length through the
sample, the reported reflection and refraction phenomena arise within a few
wavelengths at the interface and thereby suggest a new approach to polarimetry
that can be used in microfluidic volumes
An open systems approach to calculating time dependent spectra
A new method to calculate the spectrum using cascaded open systems and master
equations is presented. The method uses two state analyzer atoms which are
coupled to the system of interest, whose spectrum of radiation is read from the
excitation of these analyzer atoms. The ordinary definitions of a spectrum uses
two-time averages and Fourier-transforms. The present method uses only one-time
averages. The method can be used to calculate time dependent as well as
stationary spectra.Comment: 8 pages, revtex, 18 figures, to be published in J.Mod.Op
Ionization Mechanisms in Jet-Dominated Seyferts: A Detailed Case Study
For the past 10 years there has been an active debate over whether fast
shocks play an important role in ionizing emission line regions in Seyfert
galaxies. To investigate this claim, we have studied the Seyfert 2 galaxy Mkn
78, using HST UV/optical images and spectroscopy. Since Mkn 78 provides the
archetypal jet-driven bipolar velocity field, if shocks are important anywhere
they should be important in this object. Having mapped the emission line fluxes
and velocity field, we first compare the ionization conditions to standard
photoionization and shock models. We find coherent variations of ionization
consistent with photoionization model sequences which combine optically thick
and thin gas, but are inconsistent with either autoionizing shock models or
photoionization models of just optically thick gas. Furthermore, we find
absolutely no link between the ionization of the gas and its kinematic state,
while we do find a simple decline of ionization degree with radius. We feel
this object provides the strongest case to date against the importance of shock
related ionization in Seyferts.Comment: 4 pages, 1 figure, to appear in the proceedings of IAU Symposium 222
"The Interplay among Black Holes, Stars and ISM in Galactic Nuclei", T.
Storchi Bergmann, L.C. Ho & H.R. Schmitt, ed
Misperceptions about White Gloves
Journal ArticleCollection care and handling policies that mandate curators and/or patrons to wear gloves when handling archival and library materials need reexamining. Contrary to popular opinion, gloves provide no guarantee of protection from perspiration and dirt. Further, they increase the likelihood of physical damage occurring to paper-based collection material by blunting the sense of touch. Gloved readers and collection management personnel are deprived of information concerning the condition of material they handle as well as the aesthetic pleasure of holding artifacts. Implementing an institutionally monitored, hand-cleaning policy is a reasonable and effective alternative to protecting artifacts from damage while promoting the essential humanistic experience of touch. Such a policy follows the standard protocol employed universally by book and paper conservators when handling the same material
Dissipation enhanced vibrational sensing in an olfactory molecular switch
Motivated by a proposed olfactory mechanism based on a
vibrationally-activated molecular switch, we study electron transport within a
donor-acceptor pair that is coupled to a vibrational mode and embedded in a
surrounding environment. We derive a polaron master equation with which we
study the dynamics of both the electronic and vibrational degrees of freedom
beyond previously employed semiclassical (Marcus-Jortner) rate analyses. We
show: (i) that in the absence of explicit dissipation of the vibrational mode,
the semiclassical approach is generally unable to capture the dynamics
predicted by our master equation due to both its assumption of one-way
(exponential) electron transfer from donor to acceptor and its neglect of the
spectral details of the environment; (ii) that by additionally allowing strong
dissipation to act on the odorant vibrational mode we can recover exponential
electron transfer, though typically at a rate that differs from that given by
the Marcus-Jortner expression; (iii) that the ability of the molecular switch
to discriminate between the presence and absence of the odorant, and its
sensitivity to the odorant vibrational frequency, are enhanced significantly in
this strong dissipation regime, when compared to the case without mode
dissipation; and (iv) that details of the environment absent from previous
Marcus-Jortner analyses can also dramatically alter the sensitivity of the
molecular switch, in particular allowing its frequency resolution to be
improved. Our results thus demonstrate the constructive role dissipation can
play in facilitating sensitive and selective operation in molecular switch
devices, as well as the inadequacy of semiclassical rate equations in analysing
such behaviour over a wide range of parameters.Comment: 12 pages, 6 figures, close to published version, comments welcom
Evolutionary multiobjective optimization of the multi-location transshipment problem
We consider a multi-location inventory system where inventory choices at each
location are centrally coordinated. Lateral transshipments are allowed as
recourse actions within the same echelon in the inventory system to reduce
costs and improve service level. However, this transshipment process usually
causes undesirable lead times. In this paper, we propose a multiobjective model
of the multi-location transshipment problem which addresses optimizing three
conflicting objectives: (1) minimizing the aggregate expected cost, (2)
maximizing the expected fill rate, and (3) minimizing the expected
transshipment lead times. We apply an evolutionary multiobjective optimization
approach using the strength Pareto evolutionary algorithm (SPEA2), to
approximate the optimal Pareto front. Simulation with a wide choice of model
parameters shows the different trades-off between the conflicting objectives
High-speed, high-frequency ultrasound, \u3ci\u3ein utero\u3c/i\u3e vector-flow imaging of mouse embryos
Real-time imaging of the embryonic murine cardiovascular system is challenging due to the small size of the mouse embryo and rapid heart rate. High-frequency, linear-array ultrasound systems designed for small-animal imaging provide high-frame-rate and Doppler modes but are limited in regards to the field of view that can be imaged at fine-temporal and -spatial resolution. Here, a plane-wave imaging method was used to obtain high-speed image data from in utero mouse embryos and multi-angle, vector-flow algorithms were applied to the data to provide information on blood flow patterns in major organs. An 18-MHz linear array was used to acquire plane-wave data at absolute frame rates â„10 kHz using a set of fixed transmission angles. After beamforming, vector-flow processing and image compounding, effective frame rates were on the order of 2 kHz. Data were acquired from the embryonic liver, heart and umbilical cord. Vector-flow results clearly revealed the complex nature of blood-flow patterns in the embryo with fine-temporal and -spatial resolution
Quantitative assessment of cell fate decision between autophagy and apoptosis
Abstract Autophagy and apoptosis are cellular processes that regulate cell survival and death, the former by eliminating dysfunctional components in the cell, the latter by programmed cell death. Stress signals can induce either process, and it is unclear how cells âassessâ cellular damage and make a âlifeâ or âdeathâ decision upon activating autophagy or apoptosis. A computational model of coupled apoptosis and autophagy is built here to analyze the underlying signaling and regulatory network dynamics. The model explains the experimentally observed differential deployment of autophagy and apoptosis in response to various stress signals. Autophagic response dominates at low-to-moderate stress; whereas the response shifts from autophagy (graded activation) to apoptosis (switch-like activation) with increasing stress intensity. The model reveals that cytoplasmic Ca2+ acts as a rheostat that fine-tunes autophagic and apoptotic responses. A G-protein signaling-mediated feedback loop maintains cytoplasmic Ca2+ level, which in turn governs autophagic response through an AMP-activated protein kinase (AMPK)-mediated feedforward loop. Ca2+/calmodulin-dependent kinase kinase ÎČ (CaMKKÎČ) emerges as a determinant of the competing roles of cytoplasmic Ca2+ in autophagy regulation. The study demonstrates that the proposed model can be advantageously used for interrogating cell regulation events and developing pharmacological strategies for modulating cell decisions
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