485 research outputs found
Magnetic-field cycling induced anomalous irreversibility in resistivity of charge-ordered manganites
The rare-earth ions (RE = Eu, Dy Ho, Tm, Y) substituted charge-ordered
antiferromagnetic manganites, Pr0.45RE0.05Ca0.5MnO3, were studied for the
magnetic and the transport properties in the presence of external
magnetic-fields of up to 14 Tesla. Regardless of the intrinsic magnetic
property of RE ions, all the compounds exhibit successive step-like
metamagnetic transitions at low temperatures, which are strongly correlated to
their electronic transitions. At any fixed temperature in two different
temperature-regimes, we observed contrary effects of the magnetic-field cycling
on the resistivity of these manganites, namely, i) in the low temperature
regime (<70 K), the resistivity was irreversible showing lower values than
initial after a magnetic-field cycle was over, which is consistent with the
irreversible magnetization, and ii) in a temperature regime above 70 K, the
resistivity is irreversible with noticeably higher values than initial, whereas
the magnetization was found to be reversible. For the latter case, we further
show that this irreversibility of resistivity systematically depends on the
temperature and the magnitude of applied magnetic-field. These results suggest
that the observed resistivity behavior originated from the magnetic-field
induced metamagnetic transitions and training effect.Comment: 11 pages including 1 table and 7 figures. To appear in Europhysics
Letter
X_(CO2) retrieval error over deserts near critical surface albedo
Large retrieval errors in columnâweighted CO_2 mixing ratio (X_(CO2)) over deserts are evident in the Orbiting Carbon Observatory 2 version 7 L2 products. We argue that these errors are caused by the surface albedo being close to a critical surface albedo (α_c). Over a surface with albedo close to α_c, increasing the aerosol optical depth (AOD) does not change the continuum radiance. The spectral signature caused by changing the AOD is identical to that caused by changing the absorbing gas column. The degeneracy in the retrievals of AOD and X_(CO2) results in a loss of degrees of freedom and information content. We employ a twoâstreamâexact single scattering radiative transfer model to study the physical mechanism of X_(CO2) retrieval error over a surface with albedo close to α_c. Based on retrieval tests over surfaces with different albedos, we conclude that over a surface with albedo close to α_c, the X_(CO2) retrieval suffers from a significant loss of accuracy. We recommend a bias correction approach that has significantly improved the X_(CO2) retrieval from the California Laboratory for Atmospheric Remote Sensing data in the presence of aerosol loading
Wigner's Friend paradoxes: consistency with weak-contextual and weak-macroscopic realism models
Wigner's friend paradoxes highlight contradictions between measurements made
by Friends inside a laboratory and superobservers outside a laboratory, who
have access to an entangled state of the measurement apparatus. The
contradictions lead to no-go theorems for observer-independent facts, thus
challenging concepts of objectivity. Here, we examine the paradoxes from the
perspective of establishing consistency with macroscopic realism. We present
versions of the Brukner-Wigner-friend and Frauchiger-Renner paradoxes in which
the spin- system measured by the Friends corresponds to two
macroscopically distinct states. The local unitary operations that
determine the measurement setting are carried out using nonlinear
interactions, thereby ensuring measurements need only distinguish between the
macroscopically distinct states. The macroscopic paradoxes are perplexing,
seemingly suggesting there is no objectivity in a macroscopic limit. However,
we demonstrate consistency with a contextual weak form of macroscopic realism
(wMR): The premise wMR asserts that the system can be considered to have a
definite spin outcome , at the time after the system has
undergone the unitary rotation to prepare it in a suitable pointer
basis. We further show that the paradoxical outcomes imply failure of
deterministic macroscopic local realism, and arise when there are unitary
interactions occurring due to a change of measurement setting at
both sites, with respect to the state prepared by each Friend. In models which
validate wMR, there is a breakdown of a subset of the assumptions that
constitute the Bell-Locality premise. A similar interpretation involving a weak
contextual form of realism exists for the original paradoxes
Flavor Changing Effects in Family Nonuniversal Z' Models
Flavor-changing and CP-violating interactions of Z' to fermions are generally
present in models with extra U(1) gauge symmetry that are string-inspired or
related to broken gauged family symmetry. We study the consequences of such
couplings in fermion electric dipole moments, muon g-2, and K and B meson
mixings. From experimental limits or measured values, we constrain the
off-diagonal Z' couplings to fermions. Some of these constraints are comparable
or stronger than the existing constraints obtained from other observables.Comment: 17 pages, 2 figure
The Impact of International Labour Standards Enforcement Initiatives: The Case of the Cambodian Garment Industry
Inadequate working conditions are frequently reported within clothing manufacturing, particularly in the least developed countries where loose legislative enforcement contributes to lower labour costs that are favoured by retail buyers. Global efforts, including from the
International Labour Organisation (ILO), seek to develop better working practices however the effectiveness of such efforts are not fully understood. The research proposed focuses on Cambodia, assessing the effectiveness of two initiatives led by the ILO, namely, Better Factories Cambodia and Cambodia Decent Work Country Programme. The lens of
Institutional Theory will be used to understand the dimensions of Isomorphism and Decoupling that influence stakeholder responses to pressure to raise worker conditions. Inductive Semi-Structured Interviews are planned with ILO officials, factory owners and factory workers to gain depth understanding of key stakeholdersâ views, particularly surrounding changes enacted âon the groundâ and the motives and barriers to compliance with international standards
Pathological and Immunocytochemical Changes in Chronic Calcium Oxalate Nephrolithiasis in the Rat
In the present study, we exposed rats to a crystal-inducing diet (CID) consisting of vitamin D3 and 0.5% ethylene glycol (EG), and we investigated histologically the kidney damage induced by the deposition of calcium oxalate (CaOx) crystals. After 28 days, 50 % of the animals had renal CaOx crystals, of which 60% also had small papillary stones. Most crystals were present in the cortex. The occurrence of these crystals coincided with morphological and cytochemical changes: glomerular damage, tubular dilatation and necrosis, and an enlargement of the interstitium. The number of epithelial and interstitial cells positive for the proliferating cell nuclear antigen (PCNA) was increased. Tamm-Horsfall protein (THP) was not only demonstrable in the thick ascending limb of the loop of Henle (TAL), but also frequently in glomeruli, in the proximal tubular epithelium, and in the papilla. In the lumen of the tubular system, it was associated with urinary casts. Reflection contrast microscopy (RCM) showed that the crystals were coated with a thin layer of THP. In spite of the high urinary oxalate concentrations, the above described cellular changes were not observed in CID-fed rats without renal crystals. We conclude, therefore, that in the kidney, the retained CaOx crystals rather than the urinary oxalate ions are responsible for the observed morphological and immunocytochemical changes
Accounting for aerosol scattering in the CLARS retrieval of column averaged CO_2 mixing ratios
The California Laboratory for Atmospheric Remote Sensing Fourier transform spectrometer (CLARSâFTS) deployed at Mount Wilson, California, has been measuring column abundances of greenhouse gases in the Los Angeles (LA) basin in the nearâinfrared spectral region since August 2011. CLARSâFTS measures reflected sunlight and has high sensitivity to absorption and scattering in the boundary layer. In this study, we estimate the retrieval biases caused by aerosol scattering and present a fast and accurate approach to correct for the bias in the CLARS column averaged CO2 mixing ratio product, X_(CO2). The high spectral resolution of 0.06âcm^(â1) is exploited to reveal the physical mechanism for the bias. We employ a numerical radiative transfer model to simulate the impact of neglecting aerosol scattering on the CO_2 and O_2 slant column densities operationally retrieved from CLARSâFTS measurements. These simulations show that the CLARSâFTS operational retrieval algorithm likely underestimates CO_2 and O_2 abundances over the LA basin in scenes with moderate aerosol loading. The bias in the CO_2 and O_2 abundances due to neglecting aerosol scattering cannot be canceled by ratioing each other in the derivation of the operational product of X_(CO2). We propose a new method for approximately correcting the aerosolâinduced bias. Results for CLARS X_(CO2) are compared to directâSun X_(CO2) retrievals from a nearby Total Carbon Column Observing Network (TCCON) station. The biasâcorrection approach significantly improves the correlation between the X_(CO2) retrieved from CLARS and TCCON, demonstrating that this approach can increase the yield of useful data from CLARSâFTS in the presence of moderate aerosol loading
Microwave assisted heterogeneous catalysis: effects of varying oxygen concentrations on the oxidative coupling of methane
The oxidative coupling of methane was investigated over alumina supported La2O3/CeO2 catalysts under microwave dielectric heating conditions at different oxygen concentrations. It was observed that, at a given temperature using microwave heating, selectivities for both ethane and ethylene were notably higher when oxygen was absent than that in oxygen/methane mixtures. The differences were attributed to the localised heating of microwave radiation resulting in temperature inhomogeneity in the catalyst bed. A simplified model was used to estimate the temperature inhomogeneity; the temperature at the centre of the catalyst bed was 85 °C greater than that at the periphery when the catalyst was heated by microwaves in a gas mixture with an oxygen concentration of 12.5% (v/v), and the temperature difference was estimated to be 168 °C in the absence of oxygen
Etiology of Experimental Calcium Oxalate Monohydrate Nephrolithiasis in Rats
In a rat-model system, tubular crystal retention as a possible mechanism for the etiology of nephrolithiasis in man, was studied by conventional transmission electron microscopy. The animals were supplied for nine days with a crystal-inducing diet, with ethylene glycol plus NH4Cl in their drinking-water. After this induction period, a two day regime with fresh drinking-water was included, to allow crystals to be removed by spontaneous crystalluria. After aldehyde fixation of the rat kidneys, large crystals were seen inside the tubular lumen. The crystals were attached to cell surfaces and covered by neighboring epithelial cells. Some crystals were overgrown by several epithelial cells and underwent a process of so-called exotubulosis, resulting in free or cell-surrounded crystals in the interstitium, and possibly in crystals in Giant cells. To investigate the fate of the retained crystals, some animals were additionally exposed to a low-oxalate challenge from drinking water containing 0.1 volume per cent of ethylene glycol for 12 or 30 days, respectively. It was assumed that this would interfere with the retained intratubular or interstitial crystals, and allow the crystals to grow into mini-stones. This was not observed. After the oxalate challenge, no crystals were found to be retained in the tubules (free or covered by cells). Interstitial crystals were observed, but it remains to be demonstrated whether such crystals actually grow into mini-stones or that they are removed by the sterile inflammation process observed
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