Observation of photo-induced plasmon-phonon coupling in PbTe via ultrafast x-ray scattering

We report the observation of photo-induced plasmon-phonon coupled modes in the group IV-VI semiconductor PbTe using ultrafast x-ray diffuse scattering at the Linac Coherent Light Source. We measure the near-zone-center excited-state dispersion of the heavily screened longitudinal optical (LO) phonon branch as extracted from differential changes in x-ray diffuse scattering intensity following above bandgap photoexcitation. We suggest that upon photoexcitation, the LO phonon-plasmon coupled (LOPC) modes themselves become coupled to longitudinal acoustic modes that drive electron band shifts via acoustic deformation potentials and possibly to low-energy single-particle excitations within the plasma and that these couplings give rise to displacement-correlations that oscillate in time with a period given effectively by the heavily screened LOPC frequency.

The origin of incipient ferroelectricity in lead telluride

The interactions between electrons and lattice vibrations are fundamental to materials behaviour. In the case of group IV–VI, V and related materials, these interactions are strong, and the materials exist near electronic and structural phase transitions. The prototypical example is PbTe whose incipient ferroelectric behaviour has been recently associated with large phonon anharmonicity and thermoelectricity. Here we show that it is primarily electron-phonon coupling involving electron states near the band edges that leads to the ferroelectric instability in PbTe. Using a combination of nonequilibrium lattice dynamics measurements and first principles calculations, we find that photoexcitation reduces the Peierls-like electronic instability and reinforces the paraelectric state. This weakens the long-range forces along the cubic direction tied to resonant bonding and low lattice thermal conductivity. Our results demonstrate how free-electron-laser-based ultrafast X-ray scattering can be utilized to shed light on the microscopic mechanisms that determine materials properties.

Group IV–VI materials often exist in a state near an electronic or structural phase transition. Here, the authors use ultrafast X-ray scattering to show that coupling of band-edge electrons and phonons causes the ferroelectric instability observed in lead telluride.

[ETIOLOGY OF PROSTATE CANCER]

Prostate cancer is now recognized as one of the most important medical problems in male population. Epigenetic regulation of gene expression by promoter methylation and histone acetylation, proinflammatory enzyme cyclooxygenase-2 and somatic mutations in a variety of genes with diverse biological functions has been implicated in prostate cancer development and progression.

Temperature variable ion trap studies of C3Hn+ with H2 and HD

Hydrogenation and deuteration of C3+, C3H+, C3H2+ in collisions with H2 and HD has been studied from room temperature down to 10 K using a 22-pole ion trap. Although exothermic, hydrogenation of C3+ is rather slow at room temperature but becomes faster with decreasing temperature. In addition to the increasing lifetime of the collision complex this behavior may be caused by the floppy structure of C3+ and the freezing of soft bending modes below 50 K. For C3(+) + HD it has been shown that production of C3D+ is slightly favored over C3H+ formation. The controversy over which products are really formed in C3H(+) + H2 collisions and deuterated variants has a long history. Previous and new ion trap results prove that formation of C3H2(+) + H is not endothermic but rather fast, in contradiction to erroneous conclusions from flow tube experiments and ab initio calculations. In addition the reaction shows a complicated isotope dependence, most probably caused by the influence of zero point energies in entrance and exit transition states. For example hydrogen abstraction with HD is faster than with H2 while radiative association is slower. The most surprising result has been obtained for C3H(+) + HD. Here C3HD+ formation is over one hundred times faster than C3H2+. In addition to the details of the potential energy surface it may be that in this case an H-HD exchange reaction takes place via an open-chain propargyl cation intermediate (H2CCCH+). Reactions of C3H2+ and C3H3+ with H2 are very slow but, due to the unique sensitivity of the trapping technique, significant rate coefficients have been determined. The presented results are of fundamental importance for understanding the energetics, structures and reaction dynamics of the deuterated variant of the C3Hn+ collision system. They indicate that the previous quantum chemical calculations are not accurate enough for understanding the low energy behavior of the Cn,Hm+ reaction systems. The laboratory experiments are of essential relevance for the carbon chemistry of dense interstellar clouds, both for formation of small hydrocarbons and deuterium fractionation.

Asymmetry of Hbeta Stark profiles in T-tube hydrogen plasma

The whole Balmer H(beta) line profiles are studied in detail experimentally in the T-tube discharge for the wide range of plasma parameters. Besides the common one, two additional parameters are introduced to characterize the asymmetry behavior of the experimental Stark profiles with the reference point chosen in the center of the line. The experimental data are analyzed and benchmarked versus the simple theoretical model based on the effects of microfield nonuniformity and electron impact shifts.

[Modern treatment of leukemia and hematopoietic stem cell transplantation]

The paper presents the possibilities of contemporary treatment of acute and chronic leukemia that have been based on new knowledge and experience we have gathered through clinical and scientific work. Contemporary treatment of leukemia is very complex and requires the application of cytostatics, biological therapy and transplantation of hematopoietic stem cells. The treatment of acute leukemia by cytostatics and induction protocols results in a rather high percentage of remissions, but unfortunately most of them cannot be preserved. Allogenic transplantation of hematopoietic stem cells from bone marrow or peripheral blood have given the best results in the treatment of acute and chronic leukemia. Anti-leukemic effect is bound to the previous chemoradiotherapy, particularly to the activity of donor's immunocompetent cells in the transplant, having an effect of a graft against leukemia. The cleansing of the autograft and isolation of stem cells together with the application of IL-2 will be a significant improvement of the efficacy of autologous transplantation in leukemia. It is realistic to expect that the treatment of malignant diseases such as leukemia will in near future, besides the already existing treatment methods, include molecular therapy at various cell levels, which will make possible a correction of the basic disorder in the process of malignant alteration of hematopoietic cells.

Apolipoprotein B gene DNA polymorphisms (EcoRI and MspI) and serum lipid levels in the Serbian healthy population: interaction of rare alleles and smoking and cholesterol levels

The frequency of restriction fragment length polymorphisms (RFLPs) of the apolipoprotein B (apo B) gene, detected by EcoRI and MspI, and their influence on serum lipids were studied in a total of 239 healthy subjects from the Belgrade area. The influence of interaction between different genotypes and smoking was also studied. The relative frequency of both rare R2 and M2 alleles (lacking the cutting site) was similar to that reported in other groups of Caucasians (0.16 and 0.11, respectively). No association was observed between the apo B genotypes and serum lipid levels adjusted for age, body mass index, and blood pressure either in the whole sample or in either women or men. When smokers and non-smokers were considered separately, smoking had a significant impact on total cholesterol variability in all individuals with genotype M1M2 and high density lipoprotein (HDL) cholesterol variability in women with genotype R1R2. The presence of the rare alleles of these two polymorphisms in smokers was associated with lower lipid levels in the whole sample and in both women and men analyzed separately, except for an increase of HDL cholesterol level in male smokers, heterozygous for EcoRI polymorphism (R1R2).

[Effect of polychemotherapy in the treatment of patients with non-Hodgkin's lymphoma]

Non-Hodgkin lymphomas belong to malignant hemopathies where clinical course, histological manifestation and therapy response are characterized by diverse features. Sensitivity of the lymphoma to chemotherapy introduced drug combinations for the improvement of patient survival rate and the prognosis. The study reviews the results achieved in 85 patients with NHL treated with different cytostatic combinations (COP, CHOP, COP-BLAM, MEV, LRS-074/B). The majority of the patients (41%) had entered the IV clinical stadium (Ann Arbor) with serious histological types of the disease (LDLL-45% and histiocytic 27%). This made us decide on LRS-074/B protocol (34%) and COP-BLAM cure (20%) planned for those with the advanced clinical stage and poor histological type of the disease. The full remission was achieved in 50%, partial in 28% of the cases while in 20% of the treated patients the therapy response lacked. Relapse of the disease occurs in about 50% of the treated patients. Patients treated with LRS-074/B protocol (p < 0.05) live statistically significantly longer. In a period of 24 months 50% of those treated with LRS-074/B protocol, COP and COP-BLAM cures show no symptoms. There is no a statistically significant difference regarding the mean survival rate (p > 0.05) in relation to the histological type of the disease.

Limited polymorphism of both classes of MHC genes in four different species of the Balkan mole rat

We analyzed the restriction fragment length polymorphism of class I and class II MHC genes in DNA from 20 individuals belonging to the four different species of the complex of species of Balkan mole rats Spalax leucodon captured at four different localities in Yugoslavia. All populations were tested with four restriction enzymes and one conserved mouse probe for each of the two classes of MHC genes. The probes employed detect either limited polymorphism of class I genes or lack of polymorphic bands containing class II genes. Of the two other subterranean rodents that have been studied, four karyotype forms of the Israeli mole rat show polymorphism in both classes of MHC genes similar to the one found in all other mammals (Nizetić et al. 1985), and the Syrian hamster shows limited polymorphism of class I genes and high polymorphism of class II genes (McGuire et al. 1985). Balkan mole rats belong to a new group in this respect, different from all mammals studied so far, since they apparently show limited polymorphism of both classes of MHC genes.