119 research outputs found
The composition of wage differentials between migrants and natives
We consider the role of unobservables, such as differences in search frictions, reservation wages, and productivities for the explanation of wage differentials between migrants and natives. We disentangle these by estimating an empirical general equilibrium search model with on-the-job search due to Bontemps et al. (1999) on segments of the labour market defined by occupation, age, and nationality using a large scale German administrative dataset.
The native-migrant wage differential is then decomposed into several parts, and we focus especially on the component that we label “migrant effect”, being the difference in wage offers between natives and migrants in the same occupation-age segment in firms of the same productivity. Counterfactual decompositions of wage differentials allow us to identify and quantify their drivers, thus explaining within a common framework what is often labelled the unexplained wage gap
Dynamics of Quasi-ordered Structure in a Regio-regulated pi-Conjugated Polymer:Poly(4-methylthiazole-2,5-diyl)
Dynamics of regio-regulated Poly(4-methylthiazole-2,5-diyl) [HH-P4MeTz] was
inves tigated by solid-state 1H, 2D, 13C NMR spectroscopies, and differential
scanning calorimetry(DSC) measurements. DSC, 2D quadrupolar echo NMR, 13C
cross-polarization and magic-angle spinning(CPMAS) NMR, and 2D spin-echo(2DSE)
CPMAS NMR spectroscopy suggest existence of a quasi-ordered phase in which
backbone twists take place with weakened pi-stackings. Two-dimensional exchange
2D NMR(2DEX) detected slow dynamics with a rate of an order of 10^2Hz for the
CD_3 group in d_3-HH-P4MeTz at 288K. The frequency dependence of proton
longitudinal relaxation rate at 288K shows a omega^-1/2 dependence, which is
due to the one-dimensional diffusion-like motion of backbone conformational
modulation waves. The diffusion rate was estimated as 3+/-2 GHz, which was
approximately 10^7 times larger than that estimated by 2DEX NMR measurements.
These results suggest that there exists anomalous dispersion of modulation
waves in HH-P4MeTz. The one-dimensional group velocity of the wave packet is
responsible for the behavior of proton longitudinal relaxation time. On the
other hand, the 2DEX NMR is sensitive to phase velocity of the nutation of
methyl groups that is associated with backbone twists. From proton T_1 and T_2
measurements, the activation energy was estimated as 2.9 and 3.4 kcal/mol,
respectively. These were in agreement with 3.0 kcal/mol determined by
Moller-Plesset(MP2) molecular orbital(MO) calculation. We also performed
chemical shielding calculation of the methyl-carbon in order to understand
chemical shift tensor behavior, leading to the fact that a quasi-ordered phase
coexist with the crystalline phase.Comment: 14 pages, 11 figures, to appear in Phys.Rev.
Breakdown of the adiabatic limit in low dimensional gapless systems
It is generally believed that a generic system can be reversibly transformed
from one state into another by sufficiently slow change of parameters. A
standard argument favoring this assertion is based on a possibility to expand
the energy or the entropy of the system into the Taylor series in the ramp
speed. Here we show that this argumentation is only valid in high enough
dimensions and can break down in low-dimensional gapless systems. We identify
three generic regimes of a system response to a slow ramp: (A) mean-field, (B)
non-analytic, and (C) non-adiabatic. In the last regime the limits of the ramp
speed going to zero and the system size going to infinity do not commute and
the adiabatic process does not exist in the thermodynamic limit. We support our
results by numerical simulations. Our findings can be relevant to
condensed-matter, atomic physics, quantum computing, quantum optics, cosmology
and others.Comment: 11 pages, 5 figures, to appear in Nature Physics (originally
submitted version
CMB Telescopes and Optical Systems
The cosmic microwave background radiation (CMB) is now firmly established as
a fundamental and essential probe of the geometry, constituents, and birth of
the Universe. The CMB is a potent observable because it can be measured with
precision and accuracy. Just as importantly, theoretical models of the Universe
can predict the characteristics of the CMB to high accuracy, and those
predictions can be directly compared to observations. There are multiple
aspects associated with making a precise measurement. In this review, we focus
on optical components for the instrumentation used to measure the CMB
polarization and temperature anisotropy. We begin with an overview of general
considerations for CMB observations and discuss common concepts used in the
community. We next consider a variety of alternatives available for a designer
of a CMB telescope. Our discussion is guided by the ground and balloon-based
instruments that have been implemented over the years. In the same vein, we
compare the arc-minute resolution Atacama Cosmology Telescope (ACT) and the
South Pole Telescope (SPT). CMB interferometers are presented briefly. We
conclude with a comparison of the four CMB satellites, Relikt, COBE, WMAP, and
Planck, to demonstrate a remarkable evolution in design, sensitivity,
resolution, and complexity over the past thirty years.Comment: To appear in: Planets, Stars and Stellar Systems (PSSS), Volume 1:
Telescopes and Instrumentatio
Status of CMB Polarization Measurements from DASI and Other Experiments
We review the current status and future plans for polarization measurements
of the cosmic microwave background radiation, as well as the cosmology these
measurements will address. After a long period of increasingly sensitive upper
limits, the DASI experiment has detected the E-mode polarization and both the
DASI and WMAP experiments have detected the TE correlation. These detections
provide confirmation of the standard model of adiabatic primordial density
fluctuations consistent with inflationary models. The WMAP TE correlation on
large angular scales provides direct evidence of significant reionization at
higher redshifts than had previously been supposed. These detections mark the
beginning of a new era in CMB measurements and the rich cosmology that can be
gleaned from them.Comment: 22 pages, 9 figures; To be published in the proceedings of "The
Cosmic Microwave Background and its Polarization", New Astronomy Reviews,
(eds. S. Hanany and K.A. Olive
Modelos de crecimiento y producción en España: historia, ejemplos contemporáneos y perspectivas
En el presente trabajo se presenta una revisión sobre los modelos forestales desarrollados en España durante los últimos años, tanto para la producción maderable como no maderable y, para la dinámica de los bosques (regeneración, mortalidad). Se presentan modelos tanto de rodal completo como de clases diamétricas y de árbol individual. Los modelos desarrollados hasta la fecha se han desarrollado a partir de datos procedentes de parcelas permanentes, ensayos y el Inventario Forestal Nacional. En el trabajo se muestran los diferentes submodelos desarrollados hasta la fecha, así como las plataformas informáticas que permiten utilizar dichos modelos. Se incluyen las principales perspectivas
de desarrollo de la modelización forestal en España.In this paper we present a review of forest models developed in Spain in recent years for both timber and non timber production and forest dynamics (regeneration, mortality). Models developed are whole stand, size (diameter) class and individual-tree. The models developed to date have been developed using data from permanent plots, experimental
sites and the National Forest Inventory. In this paper we show the different sub-models developed so far and the friendly use software. Main perspectives of forest modeling in Spain are presented.The models described in this paper were funded by
different regional, national and European projects, and
some of them were elaborated by the authors. This
work was funded by the Spanish Government by the
SELVIRED network (code AGL2008-03740) and the
strategic project «Restauración y Gestión Forestal»
(code PSE-310000-2009-4)
Protein Content and Oil Composition of Almond from Moroccan Seedlings: Genetic Diversity, Oil Quality and Geographical Origin
The protein and oil content and the fatty acid profile of the kernels of selected almond genotypes from four different Moroccan regions were determined in order to evaluate the kernel quality of the plant material of these different regions. The ranges of oil content (48.7–64.5 % of kernel DW), oleic (61.8–80.2 % of total oil), linoleic (11.4–27.0 %), palmitic (5.6–7.7 %), stearic (1.3–3.1 %), and palmitoleic (0.4–0.9 %) acid percentages agreed with previous results of other almond genotypes, but the protein content (14.1–35.1 % of kernel DW) showed that some genotypes had higher values than any previously recorded in almond. Some genotypes from mountainous regions showed kernels with very high oil content as well as high and consistent oleic and linoleic ratio, establishing a possible differentiation according to the geographical origin. These differences may allow establishing a geographical denomination for almond products. In terms of genetic diversity, oleic and linoleic acids were confirmed to be the most variable components of almond oil chemical composition among genotypes. Additionally, the genotypes with extreme favorable values, such as high protein content, could be incorporated into an almond breeding program aiming at an increase in kernel quality.Peer ReviewedPrunus amygdalusProtein contentOil contentFatty acidsQualityGenetic resourcesBreedingPublishe
Instrument, Method, Brightness and Polarization Maps from the 2003 flight of BOOMERanG
We present the BOOMERanG-03 experiment and maps of the Stokes parameters I,
Q, U of the microwave sky obtained during a 14 day balloon flight in 2003.
Three regions of the southern sky were surveyed: a deep survey (~ 90 square
degrees) and a shallow survey (~ 750 square degrees) at high Galactic latitudes
(both centered at RA ~ 5.5 h, dec ~ -45 deg) and a survey of ~ 300 square
degrees across the Galactic plane at RA ~ 9.1 h, dec ~ -47 deg. All three
surveys were carried out in three wide frequency bands centered at 145, 245 and
345 GHz, with an angular resolution of ~ 10'. The 145 GHz maps of Stokes I are
dominated by Cosmic Microwave Background (CMB) temperature anisotropy, which is
mapped with high signal to noise ratio. The measured anisotropy pattern is
consistent with the pattern measured in the same region by BOOMERanG-98 and by
WMAP. The 145 GHz maps of Stokes Q and U provide a robust statistical detection
of polarization of the CMB when subjected to a power spectrum analysis. This
amplitude of the polarization is consistent with that of the CMB in the
CDM cosmological scenario. At 145 GHz, in the CMB surveys, the
intensity and polarization of the astrophysical foregrounds are found to be
negligible with respect to the cosmological signal. At 245 and 345 GHz we
detect ISD emission correlated to the 3000 GHz IRAS/DIRBE maps, and give upper
limits for any other non-CMB component. We also present intensity maps of the
surveyed section of the Galactic plane. These are compared to monitors of
different interstellar components, showing that a variety of emission
mechanisms is present in that region.Comment: see http://oberon.roma1.infn.it/boomerang/b2k and
http://cmb.phys.cwru.edu/boomerang/ for a high resolution versio
Detection of Polarization in the Cosmic Microwave Background using DASI
We report the detection of polarized anisotropy in the Cosmic Microwave
Background radiation with the Degree Angular Scale Interferometer (DASI),
located at the Amundsen-Scott South Pole research station. Observations in all
four Stokes parameters were obtained within two 3.4 FWHM fields separated by
one hour in Right Ascension. The fields were selected from the subset of fields
observed with DASI in 2000 in which no point sources were detected and are
located in regions of low Galactic synchrotron and dust emission. The
temperature angular power spectrum is consistent with previous measurements and
its measured frequency spectral index is -0.01 (-0.16 -- 0.14 at 68%
confidence), where 0 corresponds to a 2.73 K Planck spectrum. The power
spectrum of the detected polarization is consistent with theoretical
predictions based on the interpretation of CMB anisotropy as arising from
primordial scalar adiabatic fluctuations. Specifically, E-mode polarization is
detected at high confidence (4.9 sigma). Assuming a shape for the power
spectrum consistent with previous temperature measurements, the level found for
the E-mode polarization is 0.80 (0.56 -- 1.10), where the predicted level given
previous temperature data is 0.9 -- 1.1. At 95% confidence, an upper limit of
0.59 is set to the level of B-mode polarization with the same shape and
normalization as the E-mode spectrum. The TE correlation of the temperature and
E-mode polarization is detected at 95% confidence, and also found to be
consistent with predictions. These results provide strong validation of the
underlying theoretical framework for the origin of CMB anisotropy and lend
confidence to the values of the cosmological parameters that have been derived
from CMB measurements.Comment: 20 pages, 6 figure
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