17,547 research outputs found
The Theory of the Nucleon Spin
I discuss two topics of current interest in the study of the spin structure
of the nucleon. First, I discuss whether there is a sum rule for the components
of the nucleon's angular moments. Second, I discuss the measurement of the
nucleon's transversity distribution in light of recent results reported by the
HERMES collaboration at DESY.Comment: 15 pages, 8 figures, LaTeX using rspublic.cls and BoxedEPS macros; as
submitted to Phil Trans A of the Royal Society for forthcoming volume: The
Quark Structure of Matter; email correspondence to [email protected]
Impact of Extreme Climate Events on Rice-Based Farming System : Case Study at Bandung District
Bandung District is found to be an area that is vulnerable to the El-Niño Southern Oscillation (ENSO) events. Whenever ENSO occurs, this district is always suffering from drought and flood leading to significant crop production lost. The vulnerable areas to flood and drought are Bojongsoang and Ciparay. The objectives of the study are : a) to identify problems related climate risks in rice-based farming system and the adaptation of mechanism to cope with climate extreme; b) to elucidate relationship of ENSO development with rainfall variability and effect of rainfall to flood and drought occurrences; and c) to evaluate economics loss due to climate extreme. Assessment of farming system at the study sites was conducted using Rapid Rural Appraisal (RRA) method. Farmer's annual income were analyzed using frequency analysis of gross margin. The results showed that Sea Surface Temperature (SST) in Tropical Pacific has significantly affected on rainfall in Ciparay sub-District. The raise in SST anomaly is clearly a subject to delay the rainy season, to prolong the dry season period, and to decrease rainfall amount up to below normal, while the decreasing of SST anomaly resulting high intensity of rainfall in the rainy season and lower in the dry season. Whenever ENSO occurs, most farmers is always suffering from drought and flood leading to significant crop failure. Most farmers realized that climate has been changed and recently there is a trend uncertainly of rainfall pattern (proved by 84% of respondents). Nevertheless, they are still using traditional way to determine the beginning of planting season. Results showed that Benefit Cost Ratio (BCR) have smaller value in floods and droughts than normal conditions. Annual net income analysis suggests that many farmers will have negative annual income either at first or second crops fail. Based on the interviews with local authorities and farmers, it is needed to increase awareness of decision maker, extension workers and farmers to climate extremes and to improve their capacity to manage climate risks
Organic Single-Crystal Field-Effect Transistors
We present an overview of recent studies of the charge transport in the field
effect transistors on the surface of single crystals of organic
low-molecular-weight materials. We first discuss in detail the technological
progress that has made these investigations possible. Particular attention is
devoted to the growth and characterization of single crystals of organic
materials and to different techniques that have been developed for device
fabrication. We then concentrate on the measurements of the electrical
characteristics. In most cases, these characteristics are highly reproducible
and demonstrate the quality of the single crystal transistors. Particularly
noticeable are the small sub-threshold slope, the non-monotonic temperature
dependence of the mobility, and its weak dependence on the gate voltage. In the
best rubrene transistors, room-temperature values of as high as 15
cm/Vs have been observed. This represents an order-of-magnitude increase
with respect to the highest mobility previously reported for organic thin film
transistors. In addition, the highest-quality single-crystal devices exhibit a
significant anisotropy of the conduction properties with respect to the
crystallographic direction. These observations indicate that the field effect
transistors fabricated on single crystals are suitable for the study of the
\textit{intrinsic} electronic properties of organic molecular semiconductors.
We conclude by indicating some directions in which near-future work should
focus to progress further in this rapidly evolving area of research.Comment: Review article, to appear in special issue of Phys. Stat. Sol. on
organic semiconductor
A numerical study of a method for measuring the effective in situ sound absorption coefficient
The accuracy of a method [Wijnant et al., “Development and applica-
tion of a new method for the in-situ measurement of sound absorption”, ISMA 31,
Leuven, Belgium (2010).], for measurement of the effective area-averaged in situ
sound absorption coefficient is investigated. Based on a local plane wave assump-
tion, this method can be applied to sound fields for which a model is not available.
Investigations were carried out by means of finite element simulations for a typical
case. The results show that the method is a promising method for determining the
effective area-averaged in situ sound absorption coefficient in complex sound fields
Steering Entropy Revisited
Drivers aim to maintain their vehicle within a number of individualsituated safety margins. Safety margin violations are characterized by rapid strongcorrective steering. Steering entropy was introduced to quantify drivers’ efforts tomaintain their lateral safety margins. In the original steering entropy, severalcomputational assumptions were made. The objective is to scrutinize andmotivate these choices and exemplify the effects of deviations from these choiceswith data from a driver distraction study. The new optimized algorithm is shownto yield significances where a number of classical metrics fail to find anysignificance. Its sensitivity is attributed to the fact that a number of observedchanges in steering behavior all manifest in a widened steering prediction errordistribution which the algorithm picks up sensitively with its log-based weightingof prediction error outliers and its use of a prediction filter that is maximallysensitive to the spectral characteristics of the baseline data
Monitoring the Variable Interstellar Absorption toward HD 219188 with HST/STIS
We discuss the results of continued spectroscopic monitoring of the variable
intermediate-velocity (IV) absorption at v = -38 km/s toward HD 219188. After
reaching maxima in mid-2000, the column densities of both Na I and Ca II in
that IV component declined by factors >= 2 by the end of 2006. Comparisons
between HST/STIS echelle spectra obtained in 2001, 2003, and 2004 and HST/GHRS
echelle spectra obtained in 1994--1995 indicate the following: (1) The
absorption from the dominant species S II, O I, Si II, and Fe II is roughly
constant in all four sets of spectra -- suggesting that the total N(H) and the
(mild) depletions have not changed significantly over a period of nearly ten
years. (2) The column densities of the trace species C I (both ground and
excited fine-structure states) and of the excited state C II* all increased by
factors of 2--5 between 1995 and 2001 -- implying increases in the hydrogen
density n_H (from about 20 cm^{-3} to about 45 cm^{-3}) and in the electron
density n_e (by a factor >= 3) over that 6-year period. (3) The column
densities of C I and C II* -- and the corresponding inferred n_H and n_e --
then decreased slightly between 2001 and 2004. (4) The changes in C I and C II*
are very similar to those seen for Na I and Ca II. The relatively low total
N(H) and the modest n_H suggest that the -38 km/s cloud toward HD 219188 is not
a very dense knot or filament. Partial ionization of hydrogen appears to be
responsible for the enhanced abundances of Na I, C I, Ca II, and C II*. In this
case, the variations in those species appear to reflect differences in density
and ionization [and not N(H)] over scales of tens of AU.Comment: 33 pages, 6 figures, aastex, accepted to Ap
ARGOS IV: The Kinematics of the Milky Way Bulge
We present the kinematic results from our ARGOS spectroscopic survey of the
Galactic bulge of the Milky Way. Our aim is to understand the formation of the
Galactic bulge. We examine the kinematics of about 17,400 stars in the bulge
located within 3.5 kpc of the Galactic centre, identified from the 28,000 star
ARGOS survey. We aim to determine if the formation of the bulge has been
internally driven from disk instabilities as suggested by its boxy shape, or if
mergers have played a significant role as expected from Lambda CDM simulations.
From our velocity measurements across latitudes b = -5 deg, -7.5 deg and -10
deg we find the bulge to be a cylindrically rotating system that transitions
smoothly out into the disk. Within the bulge, we find a kinematically distinct
metal-poor population ([Fe/H] < -1.0) that is not rotating cylindrically. The
5% of our stars with [Fe/H] < -1.0 are a slowly rotating spheroidal population,
which we believe are stars of the metal weak thick disk and halo which
presently lie in the inner Galaxy. The kinematics of the two bulge components
that we identified in ARGOS paper III (mean [Fe/H] = -0.25 and [Fe/H] = +0.15,
respectively) demonstrate that they are likely to share a common formation
origin and are distinct from the more metal poor populations of the thick disk
and halo which are colocated inside the bulge. We do not exclude an underlying
merger generated bulge component but our results favour bulge formation from
instabilities in the early thin disk.Comment: Accepted MNRAS 25 March 2013, 12 pages, 11 figure
Charging of single Si nanocrystals by atomic force microscopy
Conducting-tip atomic force microscopy (AFM) has been used to electronically probe silicon nanocrystals on an insulating substrate. The nanocrystal samples were produced by aerosol techniques and size classified; nanocrystal size can be controlled in the size range of 2-50 nm with a size variation of less than 10%. Using a conducting tip, the charge was injected directly into the nanocrystals, and the subsequent dissipation of the charge was monitored. Estimates of the injected charge can be made by comparison of the data with an intermittent contact mode model of the AFM response to the electrostatic force produced by the stored charge
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