6,584 research outputs found
Rejuvenation and Memory in model Spin Glasses in 3 and 4 dimensions
We numerically study aging for the Edwards-Anderson Model in 3 and 4
dimensions using different temperature-change protocols. In D=3, time scales a
thousand times larger than in previous work are reached with the SUE machine.
Deviations from cumulative aging are observed in the non monotonic time
behavior of the coherence length. Memory and rejuvenation effects are found in
a temperature-cycle protocol, revealed by vanishing effective waiting times.
Similar effects are reported for the D=3$site-diluted ferromagnetic Ising model
(without chaos). However, rejuvenation is reduced if off-equilibrium
corrections to the fluctuation-dissipation theorem are considered. Memory and
rejuvenation are quantitatively describable in terms of the growth regime of
the spin-glass coherence length.Comment: Extended protocols. Accepted in Phys. Rev. B. 10 postscript figure
A new intermediate mass protostar in the Cepheus A HW2 region
We present the discovery of the first molecular hot core associated with an
intermediate mass protostar in the CepA HW2 region. The hot condensation was
detected from single dish and interferometric observations of several high
excitation rotational lines (from 100 to 880K above the ground state) of SO2 in
the ground vibrational state and of HC3N in the vibrationally excited states
v7=1 and v7=2. The kinetic temperature derived from both molecules is 160K. The
high-angular resolution observations (1.25'' x 0.99'') of the SO2
J=28(7,21)-29(6,24) line (488K above the ground state) show that the hot gas is
concentrated in a compact condensation with a size of 0.6''(430AU), located
0.4'' (300AU) east from the radio-jet HW2. The total SO2 column density in the
hot condensation is 10E18cm-2, with a H2 column density ranging from 10E23 to 6
x 10E24cm-2. The H2 density and the SO2 fractional abundance must be larger
than 10E7cm-3 and 2 x 10E-7 respectively. The most likely alternatives for the
nature of the hot and very dense condensation are discussed. From the large
column densities of hot gas, the detection of the HC3N vibrationally excited
lines and the large SO2 abundance, we favor the interpretation of a hot core
heated by an intermediate mass protostar of 10E3 Lo. This indicates that the
CepA HW2 region contains a cluster of very young stars
The Effectiveness of Different Types of Sunscreen against UV Light on Escherichia coli
Ultraviolet (UV) light from the sun damages the DNA of our skin cells which could potentially lead to development of skin cancer (Mahroos, Yaar, Phillps, Bhawan, & Gilchrest, 2002). Sunscreen is used to protect our skin from this damage. The two most commonly used sunscreens are physical and chemical sunscreens. Physical sunscreens, also referred to as mineral sunscreens, work by sitting on top of your skin and reflecting UV light, whereas chemical sunscreens penetrate the skin and absorb UV light. There are many different brands of these sunscreens in the market. We hypothesized that the physical sunscreens would serve as better protection than the chemical sunscreens due to their high cost and natural ingredients. Brands that we used that represent physical sunscreens were Badger and Goddess Garden. Brands of chemical sunscreens were Aveeno, Hawaiian Tropic, and Up & Up Target Sports. All the sunscreens were creamy and had an SPF of 30. On average, the physical sunscreens were two times more expensive than chemical sunscreens. To test our hypothesis, we used the bacterium Escherichia coli (E. coli) as a model organism and exposed it to UV light while using the various sunscreens for protection. We then counted the survival rate of the E.coli colonies that were exposed. Our results demonstrated that there was no statistical significance in sunscreen protection. We concluded that physical sunscreens are not worth their price
The complex organic molecular content in the L1517B starless core
Recent observations of the pre-stellar core L1544 and the younger starless core L1498 have revealed that complex organic molecules (COMs) are enhanced in the gas phase towards their outer and intermediate-density shells. Our goal is to determine the level of chemical complexity towards the starless core L1517B, which seems younger than L1498, and compare it with the other two previously studied cores to see if there is a chemical evolution within the cores. We have carried out 3 mm high-sensitivity observations towards two positions in the L1517B starless core: the core\u27s centre and the position where the methanol emission peaks (at a distance of similar to 5000 au from the core\u27s centre). Our observations reveal that a lower number of COMs and COM precursors are detected in L1517B with respect to L1498 and L1544, and also show lower abundances. Besides methanol, we only detected CH3O, H2CCO, CH3CHO, CH3CN, CH3NC, HCCCN, and HCCNC. Their measured abundances are similar to 3 times larger towards the methanol peak than towards the core\u27s centre, mimicking the behaviour found towards the more evolved cores L1544 and L1498. We propose that the differences in the chemical complexity observed between the three studied starless cores are a consequence of their evolution, with L1517B being the less evolved one, followed by L1498 and L1544. Chemical complexity in these cores seems to increase over time, with N-bearing molecules forming first and O-bearing COMs forming at a later stage as a result of the catastrophic depletion of CO
The Tevatron Higgs exclusion limits and theoretical uncertainties: a critical appraisal
We examine the exclusion limits set by the CDF and D0 experiments on the
Standard Model Higgs boson mass from their searches at the Tevatron in the
light of large theoretical uncertainties on the signal and background cross
sections. We show that when these uncertainties are consistently taken into
account, the sensitivity of the experiments becomes significantly lower and the
currently excluded mass range -175 GeV would be entirely reopened. The
necessary luminosity required to recover the current sensitivity is found to be
a factor of two higher than the present one.Comment: 11 pages, 5 Figures. Version published in Physics Letter B, including
an erratu
The treatment of the infrared region in perturbative QCD
We discuss the contribution coming from the infrared region to NLO matrix
elements and/or coefficient functions of hard QCD processes. Strictly speaking,
this contribution is not known theoretically, since it is beyond perturbative
QCD. For DGLAP evolution all the infrared contributions are collected in the
phenomenological input parton distribution functions (PDFs), at some relatively
low scale Q_0; functions which are obtained from a fit to the `global' data.
However dimensional regularization sometimes produces a non-zero result coming
from the infrared region. Instead of this conventional regularization
treatment, we argue that the proper procedure is to first subtract from the NLO
matrix element the contribution already generated at the same order in \alpha_s
by the LO DGLAP splitting function convoluted with the LO matrix element. This
prescription eliminates the logarithmic infrared divergence, giving a
well-defined result which is consistent with the original idea that everything
below Q_0 is collected in the PDF input. We quantify the difference between the
proposed treatment and the conventional approach using low-mass Drell-Yan
production and deep inelastic electron-proton scattering as examples; and
discuss the potential impact on the `global' PDF analyses. We present arguments
to show that the difference cannot be regarded as simply the use of an
alternative factorization scheme.Comment: 15 pages, 5 figures, title changed, text considerably modified to
improve presentation, and discussion section enlarge
Mechanical behavior of alkali-cement as function of the temperature.
This investigation reports on a comparative study of the mechanical behavior at different temperatures of three different alkali-activated fly ash pastes chemically activated using sodium silicate. A control Portland cement (OPC) was used as a reference. In an attempt to simulate the conditions prevailing in the event of accidental fire, post-thermal mechanical tests were performed to determine the residual strength. It has therefore been established that FA based cements can be fabricated for construction purposes and these materials have great potential for fire resistance applications
W boson production at hadron colliders: the lepton charge asymmetry in NNLO QCD
We consider the production of W bosons in hadron collisions, and the
subsequent leptonic decay W->lnu_l. We study the asymmetry between the rapidity
distributions of the charged leptons, and we present its computation up to the
next-to-next-to-leading order (NNLO) in QCD perturbation theory. Our
calculation includes the dependence on the lepton kinematical cuts that are
necessarily applied to select W-> lnu_l events in actual experimental analyses
at hadron colliders. We illustrate the main differences between the W and
lepton charge asymmetry, and we discuss their physical origin and the effect of
the QCD radiative corrections. We show detailed numerical results on the charge
asymmetry in ppbar collisions at the Tevatron, and we discuss the comparison
with some of the available data. Some illustrative results on the lepton charge
asymmetry in pp collisions at LHC energies are presented.Comment: 37 pages, 21 figure
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