High resolution studies of low-energy electron attachment to SF5Cl: Product anions and absolute cross sections

Low energy electron attachment to SF$_5$Cl was studied at high energy resolution by mass spectrometric detection of the product anions. Two variants of the laser photoelectron attachment (LPA) technique (Kaiserslautern) were used for determining the threshold behaviour of the yield for SF$_5^-$ formation at about 1 meV resolution, and to investigate the relative cross sections for Cl$^-$, FCl$^-$, and SF$_5^-$ formation towards higher energies (up to 1 eV) at about 20 meV resolution. Thermal swarm measurements (Birmingham) were used to place the relative LPA cross sections on an absolute scale. A trochoidal electron monochromator (Innsbruck) was used for survey measurements of the relative cross sections for the different product anions over the energy range of 0-14 eV with a resolution of 0.30 eV. Combined with earlier beam data (taken at Berlin, J. Chem. Phys. 88 (1988) 149), the present experimental results provide a detailed set of partial cross sections for anion formation in low-energy electron collisions with SF$_5$Cl

Photoluminescence and photoluminescence excitation studies of lateral size effects in Zn_{1-x}Mn_xSe/ZnSe quantum disc samples of different radii

Quantum disc structures (with diameters of 200 nm and 100 nm) were prepared from a Zn_{0.72}Mn_{0.28}Se/ZnSe single quantum well structure by electron beam lithography followed by an etching procedure which combined dry and wet etching techniques. The quantum disc structures and the parent structure were studied by photoluminescence and photoluminescence excitation spectroscopy. For the light-hole excitons in the quantum well region, shifts of the energy positions are observed following fabrication of the discs, confirming that strain relaxation occurs in the pillars. The light-hole exciton lines also sharpen following disc fabrication: this is due to an interplay between strain effects (related to dislocations) and the lateral size of the discs. A further consequence of the small lateral sizes of the discs is that the intensity of the donor-bound exciton emission from the disc is found to decrease with the disc radius. These size-related effects occur before the disc radius is reduced to dimensions necessary for lateral quantum confinement to occur but will remain important when the discs are made small enough to be considered as quantum dots.Comment: LaTeX2e, 13 pages, 6 figures (epsfig

Índice de estresse hídrico da cultura (IEHC) combinado com a temperatura de estresse diário (TED) em feijoeiro (Phaseolus vulgaris L.) submetido a diferentes frequências de irrigação.

O objetivo do presente trabalho foi estimar valores do indice de estresse hidrico da cultura combinado com a temperatura de estresse diario (IEHCc) em feijoeiro (Phaseolus vulgaris L.) submetido a cinco frequencias de irrigacao 2, 4, 8, 12 e 16 dias. Os tratamentos foram estabelecidos em blocos casualizados com 4 repeticoes. As temperaturas da copa vegetal (Tc) foram medidas, atraves do termometro a infravermelho em dois periodos de manha (entre 10 e 11 horas) e de tarde (entre 13 e 14 horas). A maior producao de graos (2755kg.ha4) foi obtida na frequencia de irrigacao de 2 dias, com perdas relativas de 0,181; 16,7; 42,5 e 61,6%, para as frequencias de 4, 8, 12 e 16 dias, respectivamente. Nao houve diferenca estatistica entre as frequencias de 2, 4 e 8 dias, para a producao. As laminas totais de agua aplicadas foram de 482,0; 439,6; 385,6; 326,5 e 290,4mm, para as frequencias de 2, 4, 8, 12 e 16 dias, respectivamente. Os valores do IEHCc estimados para o periodo da manha acompanharam os da tarde, porem, os maximos ocorreram a tarde, sendo esse o periodo recomendavel para as leituras de Tc. Um valor limite de 0,15 para o IEHCc pode ser o estipulado alem do qual havera perda significativa de rendimento da cultura do feijoeiro

Crop water stress index for beans obtained from temperature difference between canopy and air.

Canopy temperature (Tc), besides serving as a parameter to estimate crop evapotranspiration (ETc), can also be used to define water stress indexes that have the advantage to serve as a reference for the rational scheduling for irrigation for a crop. One of these indexes, which has been well disseminated, is the crop water stress index (CWSI), based on the ratio between crop resistance and aerodynamic resistance (rc/ra), whose value can be estimated by the difference between the cropy canopy and the air (Tc - Ta). A study was carried out with the objective of obtaining CWSI values for beans (Phaseolus vulgaris L.), under field conditions, in which the crop was under different irrigation scheduling; 2, 4, 8, 12 and 16 day intervals. The experiment was conducted at Sete Lagoas, Minas Gerais State, Brazil, in the period from July through October, 1995. Tc values were measured by means of infrared thermometry at two times of the day; between 10:00 and 11:00 am, and between 01:00 and 02:00 p.m. The obtained results pointed to a limit of 0,15 as a reference for the beginning of water stress to occur, which is consistent with other work and other index obtained under similar conditions

Estimativa da evapotranspiração máxima do feijoeiro (Phaseolus vulgaris L.) em função do índice de área foliar e da evaporação da água do tanque classe A.

Um metodo simples que tem sido amplamente usado na obtencao da evapotranspiracao da cultura (ET) e o padronizado pela FAO. Esse se baseia em medir a evaporacao de agua do tanque Classe A (ECA) e multiplicar por coeficientes ( do tanque e da cultura) que geracao a ET. No entanto, a estimativa dos referidos coeficientes (K, e K,) nem sempre retrata de forma satisfatoria as condicoes da cultura. Procurando-se vencer essa dificuldade, tornando-se desnecessario o uso de tais coeficientes, foi objetivo deste trabalho comporvar a boa concordancia entre a ET, calculada pelo metodo de Penman-Monteith, e o indice de area foliar (IAF) e a ECA e entre a ET, unicamente com o IAF, atraves da analise de regressao linear multipla, para o feijoeiro. A melhor relacao encontrada foi a que considerou o fator biologico (IAF) conjuntamente com o ambiental (ECA), isto e, ET = -1.304 + 0,8368.iaf + 0,5537.ECA (r2 = 0,854), comprovando a metodologia como de boa eficiencia para predizer a ET

Comparison of Zn_{1-x}Mn_xTe/ZnTe multiple-quantum wells and quantum dots by below-bandgap photomodulated reflectivity

Large-area high density patterns of quantum dots with a diameter of 200 nm have been prepared from a series of four Zn_{0.93}Mn_{0.07}Te/ZnTe multiple quantum well structures of different well width (4 nm, 6 nm, 8 nm and 10 nm) by electron beam lithography followed by Ar+ ion beam etching. Below-bandgap photomodulated reflectivity spectra of the quantum dot samples and the parent heterostructures were then recorded at 10 K and the spectra were fitted to extract the linewidths and the energy positions of the excitonic transitions in each sample. The fitted results are compared to calculations of the transition energies in which the different strain states in the samples are taken into account. We show that the main effect of the nanofabrication process is a change in the strain state of the quantum dot samples compared to the parent heterostructures. The quantum dot pillars turn out to be freestanding, whereas the heterostructures are in a good approximation strained to the ZnTe lattice constant. The lateral size of the dots is such that extra confinement effects are not expected or observed.Comment: 23 pages, LaTeX2e (amsmath, epsfig), 7 EPS figure

Behaviour of chromium isotopes in the eastern sub-tropical Atlantic Oxygen Minimum Zone

Constraints on the variability of chromium (Cr) isotopic compositions in the modern ocean are required to validate the use of Cr isotopic signatures in ancient authigenic marine sediments for reconstructing past levels of atmospheric and ocean oxygenation. This study presents dissolved Cr concentrations (CrT, where CrT = Cr(VI) + Cr(III)) and Cr isotope data (δ53Cr) for shelf, slope and open ocean waters within the oxygen minimum zone (OMZ) of the eastern sub-tropical Atlantic Ocean. Although dissolved oxygen concentrations were as low as 44–90 μmol kg−1 in the core of the OMZ, there was no evidence for removal of Cr(VI). Nonetheless, there was significant variability in seawater δ53Cr, with values ranging from 1.08 to 1.72‰. Shelf CrT concentrations were slightly lower (2.21 ± 0.07 nmol kg−1) than in open ocean waters at the same water depth (between 0 and 160 m, 2.48 ± 0.07 nmol kg−1). The shelf waters also had higher δ53Cr values (1.41 ± 0.14‰ compared to 1.18 ± 0.05‰ for open ocean waters shallower than 160 m). This is consistent with partial reduction of Cr(VI) to Cr(III), with subsequent removal of isotopically light Cr(III) onto biogenic particles. We also provide evidence for input of relatively isotopically heavy Cr from sediments on the shelf. Intermediate and deep water masses (AAIW and NADW) show a rather limited range of δ53Cr values (1.19 ± 0.09‰) and inputs of Cr from remineralisation of organic material or re-oxidation of Cr(III) appear to be minimal. Authigenic marine precipitates deposited in deep water in the open ocean therefore have the potential to faithfully record seawater δ53Cr, whereas archives of seawater δ53Cr derived from shelf sediments must be interpreted with caution

The impact of the dark matter-gas interaction on the collapse behaviour of spherical symmetric systems

If the gas in the evolving cosmic halos is dissipating energy (cooling) then due to the variation of the gravitational potential the dark matter halo also undergoes a compactification. This is well-known as Adiabatic contraction (AC). Complementary to the AC we investigate the resulting dynamical behaviour of the whole system if the backreaction of the AC of DM onto the gas is taken into account. In order to achieve sufficient high resolution also within the central halo region, we use a crude fluid approximation for the DM obeying the adiabatic contraction behaviour. Further, we restrict ourself to spherical symmetry and vanishing angular momentum of the studied matter configurations. The computations are done using a first-order Godunov type scheme. Our results show that the dynamical interaction between gas and DM may lead to significant shorter collapse times. If the gas cools the dynamical behaviour of the whole system depends strongly on the shape of the initial density profile. Our findings indicate that for a certain mass range of halo configurations the dynamical interaction between gas and DM might be important for the halo evolution and must be taken into account.Comment: 9 pages, 13 figures, accepted for publication in A&A, added reference