Pulsed Nd:YAG laser welding of AISI 304 to AISI 420 stainless steels

The technique to weld AISI 304 stainless steel to AISI 420 stainless steel with a pulsed Nd:YAG laser has been investigated. The main objective of this study was to determine the influence of the laser beam position, with respect to the joint, on weld characteristics. Specimens were welded with the laser beam incident on the joint and moved 0.1 and 0.2 mm on either side of the joint. The joints were examined in an optical microscope for cracks, pores and to determine the weld geometry. The microstructure of the weld and the heat affected zones were observed in a scanning electron microscope. An energy dispersive spectrometer, coupled to the scanning electron microscope, was used to determine variations in (weight %) the main chemical elements across the fillet weld. Vickers microhardness testing and tensile testing were carried out to determine the mechanical properties of the weld. The results of the various tests and examinations enabled definition of the best position for the incident laser beam with respect to the joint, for welding together the two stainless steels.     

Sideband cooling while preserving coherences in the nuclear spin state in group-II-like atoms

We propose a method for laser cooling group-II-like atoms without changing the quantum state of their nuclear spins, thus preserving coherences that are usually destroyed by optical pumping in the cooling process. As group-II-like atoms have a (1)S(0) closed-shell ground state, nuclear spin and electronic angular momentum are decoupled, allowing for their independent manipulation. The hyperfine interaction that couples these degrees of freedom in excited states can be suppressed through the application of external magnetic fields. Our protocol employs resolved-sideband cooling on the forbidden clock transition, (1)S(0) --> (3)P(0), with quenching via coupling to the rapidly decaying (1)P(1) state, deep in the Paschen-Back regime. This makes it possible to laser cool neutral atomic qubits without destroying the quantum information stored in their nuclear spins, as shown in two examples, (171)Yb and (87)Sr.     

Zero Modes’ Fusion Ring and Braid Group Representations for the Extended Chiral <Emphasis Type="Italic">su</Emphasis>(2) WZNW Model

A zero modes’ Fock space is constructed for the extended chiral WZNW model. It gives room to a realization of the fusion ring of representations of the restricted quantum universal enveloping algebra at an even root of unity, and of its infinite dimensional extension by the Lusztig operators We provide a streamlined derivation of the characteristic equation for the Casimir invariant from the defining relations of A central result is the characterization of the Grothendieck ring of both and in Theorem 3.1. The properties of the fusion ring in are related to the braiding properties of correlation functions of primary fields of the conformal current algebra model.      

Fluorescent Probe ABM for Screening Gastrointestinal Patient’s Immune State

The fluorescent probe-aminoderivative of benzanthrone, ABM (developed at Riga Technical University, Riga, Latvia) was used to characterize the membranes of lymphocytes of cancer patients: 46 patients with gastrointestinal diseases, 13 patients having different primary localizations with massive metastases and intoxication. Patients were divided into three groups: (1) with decreased fluorescence intensity, (2) normal fluorescence intensity, (3) increased fluorescence intensity. The lymphocytes distribution among subsets differed between groups, in correspondence to the level of florescence intensity. Surgical treatment affected the main immunological parameters and elevated the functional activity of lymphocytes. In the advanced tumors group, fluorescence intensity correlates with the survival rate. Results suggest that determination of lymphocytes functional activity by ABM can aid evaluation of the immune status in cancer patients.     

Self-consistent modelling of argon microwave discharge sustained by electromagnetic wave in dipole mode

Microwave discharges produced by travelling/standing electromagnetic waves have drawn considerable attention in recent years due to their wide application in microelectronic industry. Here are presented the axial distributions of the electrons and ions as well as those of excited atoms in an argon microwave discharge at a low gas pressure (400 mTorr) sustained by a 2.45 GHz travelling dipolar electromagnetic wave. The numerical calculations are based on a self-consistent kinetic-electrodynamic model and the results obtained are in a good agreement with the experimental data. The model yields also the magnitude of the wave power sustaining the discharge and the axial profiles of all electromagnetic-wave characteristics and the axial distribution of the neutral gas temperature.     

Serial MR imaging of intracranial metastases after radiosurgery

Purpose: To evaluate the spatiotemporal evolution of radiosurgical induced changes both in metastases and in normal brain tissue adjacent to the lesions by serial magnetic resonance (MR) imaging. Methods and Materials: Thirty-five intracranial metastases of different primaries were treated in 25 patients by single high-dose radiosurgery. MR images acquired before radiosurgery were available in all patients. Sixty-three follow-up MR studies were performed in these patients including T₂- and contrast-enhanced T₁-weighted MR images. The average follow-up time was 9 ± 5 months (mean ± standard deviation [SD]). Based on contrast-enhanced T₁-weighted MR images, tumor response was radiologically classified in the following four groups: stable disease was assumed if the average tumor diameter after treatment did not show a tumor shrinkage of more than 50% and an increase of more than 25%, partial remission as a shrinkage of tumor size of more than 50%, a disappearance of contrast-enhancing tumor as a complete remission, and an increase of tumor diameter of more than 25% as tumor progress. Moreover, we analysed signal changes on T₂-weighted images in brain parenchyma adjacent to the enhancing metastases. Results: The overall mean survival time was 10.5 ± 7 months, with a 1-year actuarial survival rate of 40%. Stable disease, partial or complete remission of the metastatic tumor was observed in 22 patients (88%). Central or homogeneous loss of contrast enhancement appeared to be a good prognostic sign for stable disease or partial remission. This association was statistically significant (p < 0.05). Three patients (12%) suffered from tumor progression. In eight patients (32%) with stable disease or partial remission, signal changes on T₂-weighted images were observed in tissue adjacent to the contrast enhancing lesions. A progression of the high signal on T₂-weighted images was seen in seven of the eight patients between 3 and 6 months after therapy, followed by a signal regression 6–18 months after irradiation. Conclusion: MR imaging is a sensitive imaging tool to evaluate tumor response as well as the presence or absence of adjacent parenchymal changes following radiosurgery. Loss of homogeneous or central contrast enhancement on Gd-enhanced MR images appeared to be a good prognostic sign for tumor response. Tumor shrinkage seems not to be dependent on time. In addition, most cases of radiation induced changes in normal brain parenchyma observed on T₂-weighted images seem to be self limited.     

Polarization transforming properties of Dove prisms

We analyze the polarization changes introduced by a rotated Dove prism on the linearly polarized light, using the Jones calculus and the exact ray trace analysis. The state of polarization changes from the linear to a mildly elliptical one when a plane wave front passes through a rotated Dove prism: its semi-major axis is nearly parallel to the input plane of polarization, for any angle of prism rotation. The interferogram contrast remains high for all shearing angles in spite of polarization changes when the Dove prism is incorporated into a rotational shearing interferometer. These results are confirmed experimentally.     

High-p(T) Tomography of d+Au and Au+Au at SPS,RHIC, and LHC

The interplay of nuclear effects on the p(T)>2 GeV inclusive hadron spectra in d+Au and Au+Au reactions at sqrt[s(NN)]=17, 200, and 5500 GeV is compared to leading order perturbative QCD calculations for elementary p+p (p+p) collisions. The competition between nuclear shadowing, Cronin effect, and jet energy loss due to medium-induced gluon radiation is predicted to lead to a striking energy dependence of the nuclear suppression/enhancement pattern in A+A reactions. We show that future d+Au data can be used to disentangle the initial and final state effects.     

Channeling of fast ions through the bent carbon nanotubes:The extended two-fluid hydrodynamic model

We investigate the interactions of charged particles with straight and bent single-walled carbon nanotubes(SWNTs)under channeling conditions in the presence of dynamic polarization of the valence electrons in carbon. This polarization is described by a cylindrical, two-fluid hydrodynamic model with the parameters taken from the recent modelling of several independent experiments on electron energy loss spectroscopy of carbon nano-structures. We use the hydrodynamic model to calculate the image potential for protons moving through four types of SWNTs at a speed of 3 atomic units. The image potential is then combined with the Doyle–Turner atomic potential to obtain the total potential in the bent carbon nanotubes.Using that potential, we also compute the spatial and angular distributions of protons channeled through the bent carbon nanotubes, and compare the results with the distributions obtained without taking into account the image potential.