4,731 research outputs found
Distribution of Relaxation Times Based on Lasso Regression: A Tool for High-Resolution Analysis of IMPS Data in Photoelectrochemical Systems
Intensity-modulated photocurrent spectroscopy (IMPS) has been largely employed in semiconductor characterization for solar energy conversion devices to probe the operando behavior with widely available facilities. However, the implementation of IMPS data analysis to complex structures, whether based on the physical rate constant model (RCM) or the assumption-free distribution of relaxation times (DRT), is generally limited to a semi-quantitative description of the charge carrier kinetics of the system. In this study, a new algorithm for the analysis of IMPS data is developed, providing unprecedented time resolution to the investigation of μs to s charge carrier dynamics in semiconductor-based systems used in photoelectrochemistry and photovoltaics. The algorithm, based on the previously developed DRT analysis, is herein modified with a Lasso regression method and available to the reader free of charge. A validation of this new algorithm is performed on a α-Fe2O3 photoanode for photoelectrochemical water splitting, identified as a standard platform in the field, highlighting multiple potential-dependent charge transfer paths, otherwise hidden in the conventional IMPS data analysis
PIXE and ToF-SIMS analysis of streaker samplers filters
This paper presents methodological innovations introduced in the characterisation of urban aerosol collected in Italy in a recent campaign. Two complementary ion beam analysis (IBA) techniques were used to analyse Nuclepore filters used in continuous streaker samplers to collect airborne particles in four Italian towns. Na to Pb elemental concentrations were obtained by particle induced X-ray emission (PIXE), while time of flight secondary ion mass spectrometry (ToF-SIMS) produced, on the same samples, time trends for several elements and molecular fragments. In addition, light attenuation measurements were used as a tracer for black carbon. The data produced by these three techniques was merged into a unique data set to address the characterisation of particulate matter sources. Correlations between elemental concentration trends (PIXE) and relative trends for molecular fragments (ToF-SIMS) and black carbon (light attenuation) have been studied by cluster and principal component analysis
Shall we dance? Recreational dance, well-being and productivity performance during COVID-19: a three-country study
Mental health issues are increasingly prevalent worldwide, emphasizing the need to research antecedents and consequences of well-being. Prior research shows that within organizations, higher levels of subjective well-being (SWB) promote productivity performance. Building on this research, the authors hypothesize that recreational dance positively influences productivity through higher SWB. Survey data from Brazil, Italy, and the United Kingdom reveal that recreational dancers are more productive than nondancers due to their higher intrinsic motivation and SWB. Dancing has an additional direct effect on productivity, beyond the mediating role of SWB. The results indicate well-being and productivity improvements in all three countries, although they show a moderating effect such that the relationship between recreational dance and SWB is stronger when social norms are perceived to be looser. This study indicates potentially far-reaching benefits that could be achieved by including recreational dance in corporate well-being programs. International dance organizations could market dance classes as a pathway to increase productivity at work and explore synergies with public health marketing to promote the benefits of recreational dance in joint international campaigns
Multitrace deformations, Gamow states, and Stability of AdS/CFT
We analyze the effect of multitrace deformations in conformal field theories
at leading order in a large N approximation. These theories admit a description
in terms of a weakly coupled gravity dual. We show how the deformations can be
mapped into boundary terms of the gravity theory and how to reproduce the RG
equations found in field theory. In the case of doubletrace deformations, and
for bulk scalars with masses in the range , the deformed
theory flows between two fixed points of the renormalization group, manifesting
a resonant behavior at the scale characterizing the transition between the two
CFT's. On the gravity side the resonance is mapped into an IR non-normalizable
mode (Gamow state) whose overlap with the UV region increases as the dual
operator approaches the free field limit. We argue that this resonant behavior
is a generic property of large N theories in the conformal window, and
associate it to a remnant of the Nambu-Goldstone mode of dilatation invariance.
We emphasize the role of nonminimal couplings to gravity and establish a
stability theorem for scalar/gravity systems with AdS boundary conditions in
the presence of arbitrary boundary potentials and nonminimal coupling.Comment: 14 pages, references added, introduction change
A TGA/FT-IR study for OC and EC quantification applied to carbonaceous aerosol collected in Milan (Italy)
International audienceCarbon analysis consists in the evaluation of the carbonaceous content of the aerosol (TC) but, more importantly, of its distribution between the two components EC (Elemental Carbon) and OC (Organic Carbon) that are characterized by different physical-chemical properties. In spite of the numerous studies focused on this topic, nowadays, a universal methodology for the determination of the two components EC and OC is not available. In fact OC and EC (also known as black carbon or soot) are operationally defined by the method of analysis and, as a consequence, different methods can produce different results. In this paper we present results on the application of TGA/FT-IR (Thermogravimetric Analysis/Fourier Transformed Infrared Spectroscopy) to the characterization of carbonaceous aerosols. The analytical methodology was applied to PM10 four-hour time resolution samples collected in Milan urban area. The method is a two-steps thermal one and bases itself on the different thermal behaviour of OC and EC. It has been set up analyzing suitable standards containing both organic and elemental carbon. Carbon quantification is achieved by on-line, continuous monitoring of CO2 infrared absorption at 2361 cm?1. A good separation between OC and EC on particulate matter samples has been obtained. Ranges and average values were respectively 12?70 µg/m3 and 20 µg/m3 for OC and 0.2?6 µg/m3 and 2 µg/m3 for EC. On average OC and EC made up respectively 29.3 (±12.8) % and 2.5 (±1.8) % of PM10 fraction. The method reliability has been verified by comparison with TOT (Thermal Optical Transmission) technique. OC and EC values determined for ambient samples of PM10 were also correlated with meteorological parameters as well as with Radon concentrations
The Submillimeter Properties of the 1 Ms Chandra Deep Field North X-ray Sample
We present submillimeter observations for 136 of the 370 X-ray sources
detected in the 1 Ms exposure of the Chandra Deep Field North. Ten of the X-ray
sources are significantly detected in the submillimeter. The average X-ray
source in the sample has a significant 850 micron flux of 1.69+/-0.27 mJy. This
value shows little dependence on the 2-8 keV flux from 5e-16 erg/cm^2/s to
1e-14 erg/cm^2/s. The ensemble of X-ray sources contribute about 10% of the
extragalactic background light at 850 microns. The submillimeter excess is
found to be strongest in the optically faint X-ray sources that are also seen
at 20 cm, which is consistent with these X-ray sources being obscured and at
high redshift (z>1).Comment: 5 pages, submitted to The Astrophysical Journal Letter
Energy's and amplitudes' positivity
In QFT, the null energy condition (NEC) for a classical field configuration
is usually associated with that configuration's stability against small
perturbations, and with the sub-luminality of these. Here, we exhibit an
effective field theory that allows for stable NEC-violating solutions with
exactly luminal excitations only. The model is the recently introduced
`galileon', or more precisely its conformally invariant version. We show that
the theory's low-energy S-matrix obeys standard positivity as implied by
dispersion relations. However we also show that if the relevant NEC-violating
solution is inside the effective theory, then other (generic) solutions allow
for superluminal signal propagation. While the usual association between
sub-luminality and positivity is not obeyed by our example, that between NEC
and sub-luminality is, albeit in a less direct way than usual.Comment: 21 pages. v2: Typos in eq. (2.41) and (2.41) corrected; discussion of
section 2.3 modified accordingly. Other sections and conclusions unchanged.
Matches the Erratum published in JHE
X-ray, Optical, and Infrared Imaging and Spectral Properties of the 1 Ms Chandra Deep Field North Sources
We present the optical, near-infrared, submillimeter, and radio follow-up
catalog of the X-ray selected sources from the 1 Ms Chandra observation of the
Hubble Deep Field North region. We have B, V, R, I, and z' magnitudes for the
370 X-ray point sources, HK' magnitudes for 276, and spectroscopic redshifts
for 182. We present high-quality spectra for 175 of these. The redshift
distribution shows indications of structures at z=0.843 and z=1.0175 (also
detected in optical surveys) which could account for a part of the
field-to-field variation seen in the X-ray number counts. The flux
contributions separated into unit bins of redshift show that the z<1
spectroscopically identified sources already contribute about one-third of the
total flux in both the hard and soft bands. We find from ratios of the X-ray
counts that the X-ray spectra are well-described by absorption of an intrinsic
Gamma=1.8 power-law, with log NH values ranging from 21 to 23.7. We estimate
that the Chandra sources that produce 87% of the HEAO-A X-ray background (XRB)
at 3 keV produce 57% at 20 keV, provided that at high energies the spectral
shape of the sources continues to be well-described by a Gamma=1.8 power-law.
However, when the Chandra contributions are renormalized to the BeppoSAX XRB at
3 keV, the shape matches fairly well the observed XRB at both energies. Thus,
whether a substantial population of as-yet undetected Compton-thick sources is
required to completely resolve the XRB above 10 keV depends critically on how
the currently discrepant XRB measurements in the 1-10 keV energy range tie
together with the higher energy XRB. (Abridged)Comment: October 2002 issue of The Astronomical Journal, 19 pages + Table 1,
Figs 2 and 6 can be found at http://www.astro.wisc.edu/~barger/cdfn.htm
The deepest X-ray look at the Universe
The origin of the X-ray background, in particular at hard (2-10 keV)
energies, has been a debated issue for more than 30 years. The Chandra deep
fields provide the deepest look at the X-ray sky and are the best dataset to
study the X-ray background. We searched the Chandra Deep Field South for X-ray
sources with the aid of a dedicated wavelet-based algorithm. We are able to
reconstruct the Log N-Log S source distribution in the soft (0.5-2 keV) and
hard (2-10 keV) bands down to limiting fluxes of 2x10^{-17} erg s^{-1} cm^{-2}
and 2x10^{-16} erg s^{-1} cm^{-2}, respectively. These are a factor ~5 deeper
than previous investigations. We find that the soft relation continues along
the extrapolation from higher fluxes, almost completely accounting for the soft
X-ray background. On the contrary, the hard distribution shows a flattening
below ~2x10^{-14} erg s^{-1} cm^{-2}. Nevertheless, we can account for >68% of
the hard X-ray background, with the main uncertainty being the sky flux itself.Comment: Accepted for publication on ApJL. Two figures, requires emulateapj5
(included
Expected and unexpected behavior of the orientational order and dynamics induced by azobenzene solutes in a nematic
We have explored the changes in the phase stability, orientational order, and dynamics of the nematic 4-cyano-4¢-n-pentylbiphenyl (5CB) doped with either the trans or the cis form of different p-azobenzene derivatives using the ESR spin-probe technique. In particular, we have studied the effects induced by each of the seven nonmesogenic 4-R-phenylazobenzenes (R = H, F, Br, CH3, CF3, On-Bu, Ot-Bu) at 1% and 7% mole fraction on the order parameter and on the shift of the nematic-isotropic transition temperature (TNI), as reported by a nitroxide spin probe, and we have tried to relate them to the solute shape and charge distribution. In all the cases the presence of the azo-derivative causes a depression of TNI, more pronounced for the cis isomers. The dependence of on the reduced temperature T*=T/TNI remains the same as that of pure 5CB in all trans-doped samples at 1% and 7% and decreases only slightly in the cis at 1%. However, we observe different and in some cases large variations (up to 25%) in for the cis at 7%, showing solute effects that go beyond the shift in TNI. Surprisingly enough, even at the highest concentration, the probe dynamics appears to be essentially independent of the nature, the configuration, and the concentration of the different solutes and very similar to that observed in the pure 5CB
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