12,774 research outputs found
Optoelectronic Properties and Excitons in Hybridized Boron Nitride and Graphene Hexagonal Monolayers
We explain the nature of the electronic band gap and optical absorption
spectrum of Carbon - Boron Nitride (CBN) hybridized monolayers using density
functional theory (DFT), GW and Bethe-Salpeter equation calculations. The CBN
optoelectronic properties result from the overall monolayer bandstructure,
whose quasiparticle states are controlled by the C domain size and lie at
separate energy for C and BN without significant mixing at the band edge, as
confirmed by the presence of strongly bound bright exciton states localized
within the C domains. The resulting absorption spectra show two marked peaks
whose energy and relative intensity vary with composition in agreement with the
experiment, with large compensating quasiparticle and excitonic corrections
compared to DFT calculations. The band gap and the optical absorption are not
regulated by the monolayer composition as customary for bulk semiconductor
alloys and cannot be understood as a superposition of the properties of
bulk-like C and BN domains as recent experiments suggested
Impegno in the work of silvia ballestra: A space of political engagement between realism and postmodernism
L’opera di Silvia Ballestra è emblematica della transizione dei cosiddetti scrittori ‘pulp’ dalla produzione giovanile dei primi anni Novanta, di taglio esplicitamente sperimentale, ironico ed auto-riflessivo, a generi e stili che si rifanno invece alla tradizione realista ed impegnata, quali il romanzo storico e
familiare, il pamphlet politico e femminista, e il giornalismo, visti come strumenti più immediati e diretti da opporre alla reazione culturale di destra dell’era berlusconiana. La raccolta di racconti Gli orsi (1994), in particolare, mostra come per Ballestra il passaggio da un’estetica postmoderna ad una più realista sia frutto di una profonda riflessione poetica sulle possibilità degli intellettuali di intervenire sulla realtà in un momento di grande urgenza
politica
Exiles/Nomads: Journeys through Language and Gender in Italian Women’s Pulp Fiction of the 1990s
Le definizioni di esilio e nomadismo elaborate da Rosi Braidotti quali metafore dell’identità postmoderna costituiscono il punto di partenza per la discussione di alcuni scrittori degli anni Novanta (Brizzi, Culicchia, Caliceti, Scarpa, Nove, Ballestra, Campo e Santacroce), la cui narrativa prende le distanze dal contesto sociale, culturale e linguistico in cui si è tradizionalmente sviluppata la narrativa italiana. I personaggi dei loro testi si sentono estranei alla propria realtà geografica e culturale, in cui sono tuttavia costretti a ricercare le radici del proprio disagio, soprattutto quando vogliono trasformarsi da esiliati in patria in soggetti nomadi, capaci cioè di identificarsi in modo positivo nella loro perenne condizione di transizione e molteplicità. I personaggi femminili, in particolare se scritti da autrici, sembrano maggiormente in grado di quelli maschili di gestire gli opposti desideri di fuga e ritorno, in virtù di una soggettività più duttile e flessibile. Al contrario, i personaggi maschili appaiono spesso inchiodati ad una concezione fissa ed immutabile della mascolinità italiana, alla quale tentano di sfuggire ma di cui continuano a subire la fatale attrazione.Ma lo volete capire che oggi il mondo è pieno digiovani ribelli che a casa non ci stanno più neanchese li ammazzano?La Gabri chiede. E dove vanno i giovani ribelli?La Natascia risponde che i giovani ribelli nonvanno in un posto preciso, ma partono all’avventuraper conoscere il mondo
The synchrotron foreground and CMB temperature-polarization cross correlation power spectrum from the first year WMAP data
We analyse the temperature-polarization cross-correlation in the Galactic
synchrotron template that we have recently developed, and between the template
and CMB temperature maps derived from WMAP data. Since the polarized
synchrotron template itself uses WMAP data, we can estimate residual
synchrotron contamination in the CMB angular spectrum. While
appears to be contamined by synchrotron, no evidence for
contamination is found in the multipole range which is most relevant for the
fit of the cosmological optical depth.Comment: Accepted for pubblication on MNRAS Lette
The inner structure of very massive elliptical galaxies: implications for the inside-out formation mechanism of z~2 galaxies
We analyze a sample of 23 supermassive elliptical galaxies (central velocity
dispersion larger than 330 km s-1), drawn from the SDSS. For each object, we
estimate the dynamical mass from the light profile and central velocity
dispersion, and compare it with the stellar mass derived from stellar
population models. We show that these galaxies are dominated by luminous matter
within the radius for which the velocity dispersion is measured. We find that
the sizes and stellar masses are tightly correlated, with Re ~ M*^{1.1}$,
making the mean density within the de Vaucouleurs radius a steeply declining
function of M*: rho_e ~ M*^{-2.2}. These scalings are easily derived from the
virial theorem if one recalls that this sample has essentially fixed (but
large) sigma_0. In contrast, the mean density within 1 kpc is almost
independent of M*, at a value that is in good agreement with recent studies of
z ~ 2 galaxies. The fact that the mass within 1 kpc has remained approximately
unchanged suggests assembly histories that were dominated by minor mergers --
but we discuss why this is not the unique way to achieve this. Moreover, the
total stellar mass of the objects in our sample is typically a factor of ~ 5
larger than that in the high redshift (z ~ 2) sample, an amount which seems
difficult to achieve. If our galaxies are the evolved objects of the recent
high redshift studies, then we suggest that major mergers were required at z >
1.5, and that minor mergers become the dominant growth mechanism for massive
galaxies at z < 1.5.Comment: 11 pages, 8 figures, accepted in MNRA
PC1643+4631A,B: The Lyman-Alpha Forest at the Edge of Coherence
This is the first measurement and detection of coherence in the intergalactic
medium (IGM) at substantially high redshift (z~3.8) and on large physical
scales (~2.5 h^-1 Mpc). We perform the measurement by presenting new
observations from Keck LRIS of the high redshift quasar pair PC 1643+4631A, B
and their Ly-alpha absorber coincidences. This experiment extends multiple
sightline quasar absorber studies to higher redshift, higher opacity, larger
transverse separation, and into a regime where coherence across the IGM becomes
weak and difficult to detect. We fit 222 discrete Ly-alpha absorbers to
sightline A and 211 to sightline B. Relative to a Monte Carlo pairing test
(using symmetric, nearest neighbor matching) the data exhibit a 4sigma excess
of pairs at low velocity splitting (<150 km/s), thus detecting coherence on
transverse scales of ~2.5 h^-1 Mpc. We use spectra extracted from an SPH
simulation to analyze symmetric pair matching, transmission distributions as a
function of redshift and compute zero-lag cross-correlations to compare with
the quasar pair data. The simulations agree with the data with the same
strength (~4sigma) at similarly low velocity splitting above random chance
pairings. In cross-correlation tests, the simulations agree when the mean flux
(as a function of redshift) is assumed to follow the prescription given by
Kirkman et al. (2005). While the detection of flux correlation (measured
through coincident absorbers and cross-correlation amplitude) is only
marginally significant, the agreement between data and simulations is
encouraging for future work in which even better quality data will provide the
best insight into the overarching structure of the IGM and its understanding as
shown by SPH simulations.Comment: 15 pages, 11 figures; accepted for publication in Astronomical
Journa
Programa de análise de qualidade de laboratórios de fertilidade (PAQLF) que usam o método Embrapa: resultados de 2001.
bitstream/CNPS/11188/1/ct1102paqlf2001.pd
Assessing composition gradients in multifilamentary superconductors by means of magnetometry methods
We present two magnetometry-based methods suitable for assessing gradients in
the critical temperature and hence the composition of multifilamentary
superconductors: AC magnetometry and Scanning Hall Probe Microscopy. The
novelty of the former technique lies in the iterative evaluation procedure we
developed, whereas the strength of the latter is the direct visualization of
the temperature dependent penetration of a magnetic field into the
superconductor. Using the example of a PIT Nb3Sn wire, we demonstrate the
application of these techniques, and compare the respective results to each
other and to EDX measurements of the Sn distribution within the sub-elements of
the wire.Comment: 7 pages, 8 figures; broken hyperlinks are due to a problem with arXi
Programa de Análise de Qualidade de Laboratórios de Fertilidade (PAQLF) que usam o método Embrapa: resultados de 2002.
No ano de 2002, o desempenho dos laboratórios participantes do PAQLF foi avaliado através dos resultados analÃticos de 12 amostras de terra. Os participantes analisaram obrigatoriamente P e K (Mehlich-1); pH (água); Ca, Mg e Al (KCl); H+Al (acetato de Ca ou SMP); e matéria orgânica (colorimétrico ou Walkey-Black); e facultativamente os micronutrientes B (água quente); Cu, Fe Mn e Zn (Mehlich- 1) e granulometria. Dos 92 laboratórios inscritos inicialmente, foram avaliados 64 laboratórios, dos quais 93,7% apresentaram conceitos A ou B e foram habilitados ao uso do selo de qualidade. Destes, 13 laboratórios (20,3%) obtiveram conceito A. A ordem decrescente do número total de asteriscos nas análises de rotina foi P > matéria orgânica > K > Mg > H+Al > Ca > pH > Al. Para os micronutrientes, a ordem foi Fe > Mn > Zn > Cu > B, e para granulometria, silte > argila > areia. Os coeficientes de variação dos parâmetros analisados nas 12 amostras do ano pelos participantes foram, em ordem decrescente, Al > Mg > Ca > K > H+Al > P > matéria orgânica > pH, sendo que os valores ficaram na faixa de 158 a 4%. Para os micronutrientes, a ordem foi B > Zn > Cu > Fe > Mn, com valores entre 162 a 16%. Para granulometria, foi silte > argila > areia, com valores de 43, 29, e 12%.bitstream/CNPS/11568/1/comtec_14_2003_paqlf_result_2002.pd
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