Assimilation Process (assimilation + process)

Distribution by Scientific Domains

Selected Abstracts

Migrant Assimilation in Europe: A Transnational Family Affair1

Sam Scott
The paper advances our empirical and theoretical understanding of migrant assimilation. It does so by focusing on a very particular group of individuals who appear more likely than other migrant types to "go native." We call these individuals "mixed nationality relationship migrants" (i.e., migrants who have committed to a life outside their home country because of the presence of a foreign partner). The paper argues that the transnational family milieus that emerge from this form of international migration are critical to the assimilation process. Empirical material from 11 in-depth interviews with female migrants in Britain (Sheffield) and France (Paris) supports our argument. We also suggest that such "extreme" assimilation is more likely within a regional migratory system , like the EU , where the "identity frontiers" crossed in the formation of a transnational family are relatively shallow. [source]

Assimilation, Ethnic Competition, and Ethnic Identities of U.S.-Born Persons of Mexican Origin

Hiromi Ono
Processes governing the ethnic identification of second and later generations of Mexican immigrant descendants are explored empirically using the Latino National Political Survey, 1989,1990. With multinomial logit regressions, I test hypotheses based on three contrasting perspectives, namely, that ethnic identification, or identification other than "American," arises directly from: a) cultural continuity and a lower level of assimilation; b) an experience of ethnic competition; and c) both processes. The results from the LNPS support the view that both processes are at work. For example, consistent with the presence of an assimilation process, the chance of "Mexican" identification (as opposed to "American" identification) declines to half in the third generation and to one tenth in the fourth and later generations, relative to the chance in the second generation. Consistent with the presence of an ethnic competition process, (perceived) experience of discrimination doubles the respondent's chance of "Mexican" identification. Also, a level rise in the darkness of skin color is associated with a 60 percent increase in the chance of Mexican identification. [source]

Simultaneous state estimation and attenuation correction for thunderstorms with radar data using an ensemble Kalman filter: tests with simulated data

Ming Xue
Abstract A new approach to dealing with attenuated radar reflectivity data in the data assimilation process is proposed and tested with simulated data using the ensemble square-root Kalman filter. This approach differs from the traditional method where attenuation is corrected in observation space first before observations are assimilated into numerical models. We build attenuation correction into the data assimilation system by calculating the expected attenuation within the forward observation operators using the estimated atmospheric state. Such a procedure does not require prior assumption about the types of hydrometeor species along the radar beams, and allows us to take advantage of knowledge about the hydrometeors obtained through data assimilation and state estimation. Being based on optimal estimation theory, error and uncertainty information on the observations and prior estimate can be effectively utilized, and additional observed parameters, such as those from polarimetric radar, can potentially be incorporated into the system. Tests with simulated reflectivity data of an X-band 3 cm wavelength radar for a supercell storm show that the attenuation correction procedure is very effective,the analyses obtained using attenuated data are almost as good as those obtained using unattenuated data. The procedure is also robust in the presence of moderate dropsize-distribution-related observation operator error and when systematic radar calibration error exists. The analysis errors are very large if no attenuation correction is applied. The effect of attenuation and its correction when radial velocity data are also assimilated is discussed as well. In general, attenuation correction is equally important when quality radial velocity data are also assimilated. Copyright 2009 Royal Meteorological Society [source]

Accounting for an imperfect model in 4D-Var

Yannick Tr'emolet
Abstract In most operational implementations of four-dimensional variational data assimilation (4D-Var), it is assumed that the model used in the data assimilation process is perfect or, at least, that errors in the model can be neglected when compared to other errors in the system. In this paper, we study how model error could be accounted for in 4D-Var. We present three approaches for the formulation of weak-constraint 4D-Var: estimating explicitly a model-error forcing term, estimating a representation of model bias or, estimating a four-dimensional model state as the control variable. The consequences of these approaches with respect to the implementation and the properties of 4D-Var are discussed. We show that 4D-Var with an additional model-error representation as part of the control variable is essentially an initial-value problem and that its characteristics are very similar to that of strong constraint 4D-Var. Taking the four-dimensional state as the control variable, however, leads to very different properties. In that case, weak-constraint 4D-Var can be interpreted as a coupling between successive strong-constraint assimilation cycles. A possible extension towards long-window 4D-Var and possibilities for evolutions of the data assimilation system are presented. Copyright 2006 Royal Meteorological Society [source]

Ecophysiological controls over the net ecosystem exchange of mountain spruce stand.

Comparison of the response in direct vs. diffuse solar radiation
Abstract Cloud cover increases the proportion of diffuse radiation reaching the Earth's surface and affects many microclimatic factors such as temperature, vapour pressure deficit and precipitation. We compared the relative efficiencies of canopy photosynthesis to diffuse and direct photosynthetic photon flux density (PPFD) for a Norway spruce forest (25-year-old, leaf area index 11 m2 m,2) during two successive 7-day periods in August. The comparison was based on the response of net ecosystem exchange (NEE) of CO2 to PPFD. NEE and stomatal conductance at the canopy level (Gcanopy) was estimated from half-hourly eddy-covariance measurements of CO2 and H2O fluxes. In addition, daily courses of CO2 assimilation rate (AN) and stomatal conductance (Gs) at shoot level were measured using a gas-exchange technique applied to branches of trees. The extent of spectral changes in incident solar radiation was assessed using a spectroradiometer. We found significantly higher NEE (up to 150%) during the cloudy periods compared with the sunny periods at corresponding PPFDs. Prevailing diffuse radiation under the cloudy days resulted in a significantly lower compensation irradiance (by ca. 50% and 70%), while apparent quantum yield was slightly higher (by ca. 7%) at canopy level and significantly higher (by ca. 530%) in sun-acclimated shoots. The main reasons for these differences appear to be (1) more favourable microclimatic conditions during cloudy periods, (2) stimulation of photochemical reactions and stomatal opening via an increase of blue/red light ratio, and (3) increased penetration of light into the canopy and thus a more equitable distribution of light between leaves. Our analyses identified the most important reason of enhanced NEE under cloudy sky conditions to be the effective penetration of diffuse radiation to lower depths of the canopy. This subsequently led to the significantly higher solar equivalent leaf area compared with the direct radiation. Most of the leaves in such dense canopy are in deep shade, with marginal or negative carbon balances during sunny days. These findings show that the energy of diffuse, compared with direct, solar radiation is used more efficiently in assimilation processes at both leaf and canopy levels. [source]

"Reactive Ethnicity" or "Assimilation"?

Arguments, First Empirical Evidence for Labor Migrants in Germany, Statements
In this article, we scrutinize the often stated assumption that labor migrants in Germany turn away from integration and reaffirm their ethnicity by examining their identificational, cognitive, and social assimilation processes. Using data from the German Socio-economic Panel, we present trend analyses of different hostland- and homeland-related indicators for the past fifteen years. Results are presented separately for first- and second-generation migrants from Turkey, the EU, and the former Yugoslavia. While not all assimilation-related indicators change a great deal over time, they show at least a substantial difference between the first and the second generation. With regard to the homeland-related indicators, the results by no means suggest that Turkish migrants try to compensate for their comparatively disadvantaged social status by revitalizing ethnic cultural habits or homeland-oriented identifications. [source]

Structure,function studies of glutamate synthases: A class of self-regulated iron-sulfur flavoenzymes essential for nitrogen assimilation

IUBMB LIFE, Issue 5 2008
Maria Antonietta Vanoni
Abstract Glutamate synthases play with glutamine synthetase an essential role in nitrogen assimilation processes in microorganisms, plants, and lower animals by catalyzing the net synthesis of one molecule of L -glutamate from L -glutamine and 2-oxoglutarate. They exhibit a modular architecture with a common subunit or region, which is responsible for the L -glutamine-dependent glutamate synthesis from 2-oxoglutarate. Here, a PurF- (Type II- or Ntn-) type amidotransferase domain is coupled to the synthase domain, a (,/,)8 barrel containing FMN and one [3Fe-4S]0,+1 cluster, through a ,30 -long intramolecular tunnel for the transfer of ammonia between the sites. In bacterial and eukaryotic GltS, reducing equivalents are provided by reduced pyridine nucleotides thanks to the stable association with a second subunit or region, which acts as a FAD-dependent NAD(P)H oxidoreductase and is responsible for the formation of the two low potential [4Fe-4S]+1,+2 clusters of the enzyme. In photosynthetic cells, reduced ferredoxin is the physiological reductant. This review focus on the mechanism of cross-activation of the synthase and glutaminase reactions in response to the bound substrates and the redox state of the enzyme cofactors, as well as on recent information on the structure of the ,, protomer of the NADPH-dependent enzyme, which sheds light on the intramolecular electron transfer pathway between the flavin cofactors. 2008 IUBMB IUBMB Life, 60(5): 287,300, 2008 [source]