Electron pair emission from surfaces: Photon versus electron excitation

We have studied the electron pair emission process from a Cu(111) surface excited by a primary electron or photon beam. Although the photon energy was 30 eV the primary electron beam had an energy of 25 eV. We will discuss the energy and momentum distributions. The experiments with the electron beam demonstrate that the contributions from the Shockley surface state can be clearly identified. This is not the case for the work with photons which we ascribe to the low spectral weight of the contribution from two Shockley state electrons compared to two 3d electrons. The momentum distributions reveal a close similarity between the two types of excitation despite the fact that the microscopic origin of the pair emission is very different. There is a distinctive energy dependence of these curves which we describe by an empirical three-parameter polynomial. The numerical values of these parameters are close for both pathways. Additional measurements with different primary electron energies reveals the importance of the initial state on the momentum distributions

Triple electron emission from surfaces: Energy and angle relations

We discuss a proof-of-principle experiment in which we detect triple electron emission from a surface due to primary electron impact. The new aspect is the ability to record the energies and emission directions of the ejected electrons. We selected NiO films as a target, which have shown in previous electron pair emission studies to give an enhanced intensity compared to other materials. The triple sum energy spectrum displays a shape consistent with a self-convolution of the electronic density of states. We define two different emission geometries. While the energy distributions are essentially identical, the intensity levels differ by a factor of 2. Imposing a geometrical constraint on one of the emitted triples shows that the available energy is equally shared among the other two electrons. We discuss our findings within a simplified scattering model. We also present angular distributions. Prominent intensity minima for electron emission in the same direction are not observed in contrast to our previous electron pair emission studies

TESS. La banca dati on-line dei rivestimenti a mosaico

A project undertaken by the University of Padua has developed the new database system TESS for mosaics. This database system meets the national standards required by the Istituto Centrale per il Catalogo e la Documentazione – ICCD. The database is available on-line thanks to the project «Cultural heritage in the Adriatic area: knowledge, preservation and enhancement», co-financed by the Community Initiative INTERREG III A – Adriatic Cross Border Programme. In detail, the database TESS includes informative files regarding Building and Rooms, Location, relevant Bibliography and Mosaic Pavement. Each file contains plans, designs and photographs. Furthermore, all the fields have a list of univocal and exhaustive terms in the Italian language. The mosaics database aims to provide a key working tool for the identification of the origins of iconographic themes, their geographic distribution and the development of local fashions which vary according to the context. The software was developed on a FileMaker client/server environment to achieve these key goals: multiplatform availability (Windows/Macintosh), multiuser capability and remote connectivity. Making wide use of the latest tools included in FileMaker 8, the development group created a smart and complete GUI to access the complex data structure, and at the same time implemented a stringent control of user privileges by setting data-related group policies. The result is a powerful middleware application that allows data entry, analysis and publication to geographically distributed operators and will provide data consultation to other users through normal web browsers

Determination of the Earth's pole tide Love number k₂ from observations of polar motion using an adaptive Kalman filter approach

The geophysical interpretation of observed time series of Earth rotation parameters (ERP) is commonly based on numerical models that describe and balance variations of angular momentum in various subsystems of the Earth. Naturally, models are dependent on geometrical, rheological and physical parameters. Many of these are weakly determined from other models or observations. In our study we present an adaptive Kalman filter approach for the improvement of parameters of the dynamic Earth system model DyMEG which acts as a simulator of ERP. In particular we focus on the improvement of the pole tide Love number k(2). In the frame of a sensitivity analysis k(2) has been identified as one of the most crucial parameters of DyMEG since it directly influences the modeled Chandler oscillation. At the same time k(2) is one of the most uncertain parameters in the model. Our simulations with DyMEG cover a period of 60 years after which a steady state of k(2) is reached. The estimate for k(2), accounting for the anelastic response of the Earth's mantle and the ocean, is 0.3531 + 0.0030i. We demonstrate that the application of the improved parameter k(2) in DyMEG leads to significantly better results for polar motion than the original value taken from the Conventions of the International Earth Rotation and Reference Systems Service (IERS)

Free Thyroxine Level in the High Normal Reference Range Prescribed for Nonpregnant Women May Reduce the Preterm Delivery Rate in Multiparous

Preterm birth is the most common reason for perinatal morbidity and mortality in the western world. It has been shown that in euthyreotic pregnant women with thyroid autoimmune antibodies, L-Thyroxine replacement reduces preterm delivery rate in singleton pregnancies. We investigated in a nonrandomized retrospective observational study whether L-Thyroxine replacement, maintaining maternal free thyroxine serum level in the high normal reference range prescribed for nonpregnant women also influences the rate of preterm delivery in women without thyroid autoimmune antibodies. As control group for preterm delivery rate, data from perinatal statistics of the State of Baden-Württemberg from 2006 were used. The preterm delivery rate in the study group was significantly reduced. The subgroup analysis shows no difference in primiparous but a decline in multiparous by approximately 61% with L-Thyroxine replacement. Maintaining free thyroxine serum level in the high normal reference range prescribed for nonpregnant women may reduce the preterm delivery rate

Resistance, remission, and qualitative differences in HIV chemotherapy.

To understand the role of qualitative differences in multidrug chemotherapy for human immunodeficiency virus (HIV) infection in virus remission and drug resistance, we designed a mathematical system that models HIV multidrug chemotherapy including uninfected CD4+ T cells, infected CD4+ T cells, and virus populations. The model, which includes the latent and progressive stages of the disease and introduces chemotherapy, is a system of differential equations describing the interaction of two distinct classes of HIV (drug-sensitive [wild type] and drug-resistant [mutant]) with lymphocytes in the peripheral blood; the external lymphoid system contributes to the viral load. The simulations indicate that to preclude resistance, antiviral drugs must be strong enough and act fast enough to drive the viral population below a threshold level. The threshold depends upon the capacity of the virus to mutate to strains resistant to the drugs. Above the threshold, mutant strains rapidly replace wild-type strains. Below the threshold, resistant strains do not become established, and remission occurs. An important distinction between resistance and remission is the reduction of viral production in the external lymphoid system. Also the virus population rapidly rebounds when treatment is stopped even after extended periods of remission

Quantification of soil mapping by digital analysis of LANDSAT data

Soil survey mapping units are designed such that the dominant soil represents the major proportion of the unit. At times, soil mapping delineations do not adequately represent conditions as stated in the mapping unit descriptions. Digital analysis of LANDSAT multispectral scanner (MSS) data provides a means of accurately describing and quantifying soil mapping unit composition. Digital analysis of LANDSAT MSS data collected on 9 June 1973 was used to prepare a spectral soil map for a 430-hectare area in Clinton County, Indiana. Fifteen spectral classes were defined, representing 12 soil and 3 vegetation classes. The 12 soil classes were grouped into 4 moisture regimes based upon their spectral responses; the 3 vegetation classes were grouped into one all-inclusive class

Double photoemission from Ag and Pd surfaces: Energy relations

We have investigated the electron pair emission due to single-photon absorption from Ag(100) and Pd(100) surfaces. We are interested in the energy spectra of pairs in particular near the energy cutoff. The sum energy spectra of Ag display a distinctive photon energy dependence. We also observe some fine structure. Near the high-energy cutoff the coincidence rate is too low to determine the energy position of the cutoff. Nevertheless we observe a finite signal if two 5sp electrons near the Fermi level are emitted. For Pd(100) we find sum energy spectra without fine structure and the cutoff region is approached linearly. Within the experimental accuracy the minimum energy to liberate two electrons is twice the work function

Dynamics of magnetic domain wall motion after nucleation: Dependence on the wall energy

The dynamics of magnetic domain wall motion in the FeNi layer of a FeNi/Al2O3/Co trilayer has been investigated by a combination of x-ray magnetic circular dichroism, photoelectron emission microscopy, and a stroboscopic pump-probe technique. The nucleation of domains and subsequent expansion by domain wall motion in the FeNi layer during nanosecond-long magnetic field pulses was observed in the viscous regime up to the Walker limit field. We attribute an observed delay of domain expansion to the influence of the domain wall energy that acts against the domain expansion and that plays an important role when domains are small.Comment: Accepted for publication in Physical Review Letter