703 research outputs found
The Validity and Reliability of Co-heating Tests Made on Highly Insulated Dwellings
AbstractThe ability of a co-heating test to accurately identify a dwelling's envelope heat-loss coefficient has been explored using dynamic thermal simulation techniques, against a number of fabric specifications ranging from 1990 UK regulation levels through to modern Passivhaus requirements.Simple analysis methods can underestimate the heat-loss coefficient, by up to 50% for the highest performance standards considered. Using the best test and analysis methods found the envelope heat loss coefficient could be determined for current stock to better than 10% accuracy in a three week test duration. However that accuracy could not be reliably achieved in a shorter period, nor could it be achieved with a dwelling specification representing emerging standards of insulation, unless longer test periods were used
Nonvanishing Cosmological Constant of Flat Universe in Brane-World Scenario
The finite temperature effect is examined in Randall-Sundrum brane-world
scenario with inclusion of the matter fields on the brane. At zero temperature
it is found that the theory on the brane is conformally invariant, which
guarantees /CFT. At 4d effective action we derived a temperature-dependent
nonvanishing cosmological constant at the flat spacetime limit of brane
worldvolume. At the cosmological temperature the cosmological
constant is roughly which is within the upper bound of the
recent experimental value Comment: 10 pages, 1 figure; V2 12 pages, figure removed, the contribution of
matter to the cosmological constant is added, will appear in PL
3D chemical characterization of frozen hydrated hydrogels using ToF-SIMS with argon cluster sputter depth profiling
Hydrogels have been used extensively in bioengineering as artificial cell culture supports. Investigation of the interrelationship between cellular response to the hydrogel and its chemistry ideally requires methods that allow characterization without labels and can map species in three dimensional to follow biomolecules adsorbed to, and absorbed into, the open structure before and during culture. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) has the potential to be utilized for through thickness characterization of hydrogels. The authors have established a simple sample preparation procedure to successfully achieve analysis of frozen hydrated hydrogels using ToF-SIMS without the need for dry glove box entry equipment. They demonstrate this on a poly(2-hydroxyethyl methacrylate) (pHEMA) film where a model protein (lysozyme) is incorporated using two methods to demonstrate how protein distribution can be determined. A comparison of lysozyme incorporation is made between the situation where the protein is present in a polymer dip coating solution and where lysozyme is in an aqueous medium in which the film is incubated. It is shown that protonated water clusters H(H2O)nþ where n ¼ 5–11 that are indicative of ice are detected through the entire thickness of the pHEMA. The lysozyme distribution through the pHEMA hydrogel films can be determined using the intensity of a characteristic amino acid secondary ion fragment
Compromise of Localized Graviton with a Small Cosmological Constant in Randall-Sundrum Scenario
A new mechanism which leads to a linearized massless graviton localized on
the brane is found in the /CFT setting, {\it i.e.} in a single copy of
spacetime with a singular brane on the boundary, within the
Randall-Sundrum brane-world scenario. With an help of a recent development in
path-integral techniques, a one-parameter family of propagators for linearized
gravity is obtained analytically, in which a parameter reflects various
kinds of boundary conditions that arise as a result of the half-line
constraint. In the case of a Dirichlet boundary condition () the
graviton localized on the brane can be massless {\it via} coupling constant
renormalization. Our result supports a conjecture that the usual
Randall-Sundrum scenario is a regularized version of a certain underlying
theory.Comment: 6 pages, no figure, V2 12 pages, one more author added, will appear
in PL
Newton Law on the Generalized Singular Brane with and without 4d Induced Gravity
Newton law arising due to the gravity localized on the general singular brane
embedded in bulk is examined in the absence or presence of the 4d
induced Einstein term. For the RS brane, apart from the subleading correction,
Newton potential obeys 4d-type and -type gravitational law at long- and
short-ranges if it were not for the induced Einstein term. The 4d induced
Einstein term generates an intermediate range at short distance, in which the
Newton potential emerges. For Neumann brane the long-range
behavior of Newton potential is exponentially suppressed regardless of the
existence of the induced Einstein term. For Dirichlet brane the expression of
Newton potential is dependent on the renormalized coupling constant .
At particular value of Newton potential on Dirichlet brane exhibits a
similar behavior to that on RS brane. For other values the long-range behavior
of Newton potential is exponentially suppressed as that in Neumann brane.Comment: 27 pages, 2 postscript figures included V1 figures are improved and
few comments are added for further discussion. version to appear in NP
Kinks in the Hartree approximation
The topological defects of the lambda phi^4 theory, kink and antikink, are
studied in the Hartree approximation. This allows us to discuss quantum effects
on the defects in both stationary and dynamical systems. The kink mass is
calculated for a number of parameters, and compared to classical, one loop and
Monte Carlo results known from the literature. We discuss the thermalization of
the system after a kink antikink collision. A classical result, the existence
of a critical speed, is rederived and shown for the first time in the quantum
theory. We also use kink antikink collisions as a very simple toy model for
heavy ion collisions and discuss the differences and similarities, for example
in the pressure. Finally, using the Hartree Ensemble Approximation allows us to
study kink antikink nucleation starting from a thermal (Bose Einstein)
distribution. In general our results indicate that on a qualitative level there
are few differences with the classical results, but on a quantitative level
there are some import ones.Comment: 20 pages REVTeX 4, 17 Figures. Uses amsmath.sty and subfigure.sty.
Final version, fixed typo in published versio
Revealing cytokine-induced changes in the extracellular matrix with secondary ion mass spectrometry
AbstractCell-secreted matrices (CSMs), where extracellular matrix (ECM) deposited by monolayer cell cultures is decellularized, have been increasingly used to produce surfaces that may be reseeded with cells. Such surfaces are useful to help us understand cell–ECM interactions in a microenvironment closer to the in vivo situation than synthetic substrates with adsorbed proteins. We describe the production of CSMs from mouse primary osteoblasts (mPObs) exposed to cytokine challenge during matrix secretion, mimicking in vivo inflammatory environments. Time-of-flight secondary ion mass spectrometry data revealed that CSMs with cytokine challenge at day 7 or 12 of culture can be chemically distinguished from one another and from untreated CSM using multivariate analysis. Comparison of the differences with reference spectra from adsorbed protein mixtures points towards cytokine challenge resulting in a decrease in collagen content. This is supported by immunocytochemical and histological staining, demonstrating a 44% loss of collagen mass and a 32% loss in collagen I coverage. CSM surfaces demonstrate greater cell adhesion than adsorbed ECM proteins. When mPObs were reseeded onto cytokine-challenged CSMs they exhibited reduced adhesion and elongated morphology compared to untreated CSMs. Such changes may direct subsequent cell fate and function, and provide insights into pathological responses at sites of inflammation
Volatiles in lunar felsite clasts: Impact-related delivery of hydrous material to an ancient dry lunar crust
In this detailed geochemical, petrological, and microstructural study of felsite clast materials contained in Apollo breccia samples 12013, 14321, and 15405, little evidence was found for relatively enriched reservoirs of endogenic lunar volatiles. NanoSIMS measurements have revealed very low volatile abundances (≤2–18 ppm hydrogen) in nominally anhydrous minerals (NAMS) plagioclase, potassic alkali feldspar, and SiO2 that make up a majority of these felsic lithologies. Yet these mineral assemblages and clast geochemistries on Earth would normally yield relatively high volatiles contents in their NAMS (∼20 to ≥80 ppm hydrogen). This difference is particularly notable in felsite 14321,1062 that exhibits extremely low volatile abundances (≤2 ppm hydrogen) and a relatively low amount of microstructural evidence for shock metamorphism given that it is a clast of the most evolved (∼74 wt.% SiO2) rock-type returned from the Moon. If taken at face value, ‘wet’ felsic magmas (∼1.2–1.7 wt.% water) are implied by the relatively high hydrogen contents of feldspar in felsite clasts in Apollo samples 12013 and 15405, but these results are likely misleading. These felsic clasts have microstructural features indicative of significantly higher shock stress than 14321,1062. These crustal lithologies likely obtained no more water from the lunar interior than the magma body producing 14321,1062. Rather, we suggest hydrogen was enriched in samples 12013 and 15405 by impact induced exchange, and/or partial assimilation of volatiles added to the surface of the Moon by a hydrated impactor (asteroid or comet) or the solar wind. Thus, the best estimate for magmatic water contents of felsic lunar magmas comes from 14321,1062 that leads to a calculated magmatic water content of ≤0.2 wt.%. This dry felsic magma has a slightly greater, but comparable water content to the ancient mafic magmas implied by the other lithologies that we have studied. Based on this and expanding evidence for a significantly dry ancient or early degassed Moon it is likely that some recent estimates (100's ppm) of the water abundances in the lunar parental magma ocean have been overestimated
Fock-Darwin-like quantum dot states formed by charged Mn interstitial ions
We report a method of creating electrostatically induced quantum dots by thermal diffusion of interstitial Mn ions out of a p-type (GaMn)As layer into the vicinity of a GaAs quantum well. This approach creates deep, approximately circular, and strongly confined dotlike potential minima in a large (200  μm) mesa diode structure without need for advanced lithography or electrostatic gating. Magnetotunneling spectroscopy of an individual dot reveals the symmetry of its electronic eigenfunctions and a rich energy level spectrum of Fock-Darwin-like states with an orbital angular momentum component |lz| from 0 to 11
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