Transverse effects in multifrequency Raman generation

The theory of ultrabroadband multifrequency Raman generation is extended, for the first time, to allow for beam-propagation effects in one and two transverse dimensions. We show that a complex transverse structure develops even when diffraction is neglected. In the general case, we examine how the ultrabroadband multifrequency Raman generation process is affected by the intensity, phase quality, and width of the input beams, and by the length of the Raman medium. The evolution of power spectra, intensity profiles, and global characteristics of the multifrequency beams are investigated and explained. In the two-dimensional transverse case, bandwidths comparable to the optical carrier frequency, spanning the whole visible spectrum and beyond, are still achievable

Microstructure and superconducting properties of hot isostatically pressed MgB2

Bulk samples of MgB2 have been formed by hot isostatic pressing (HIPping) of commercial powder at 100MPa and 950=B0C. The resulting material is 100% dense with a sharp superconducting transition at 37.5K. Microstructural studies have indicated the presence of small amounts of second phases within the material, namely MgO and B rich compositions, probably MgB4. Magnetisation measurements performed at 20K have revealed values of Jc=1.3 x 106A/cm2 at zero field, and 9.3 x 105A/cm2 at 1T. Magneto optical (MO) studies have shown direct evidence for the superconducting homogeneity and strong intergranular current flow in the material.Comment: 3 pages, 6 figures, text updated, new references included and discussed. Submitted to Superconductor Science and Technolog

Absorption-Fluctuation Theorem for Nuclear Reactions: Brink-Axel, Incomplete Fusion and All That

We discuss the connection between absorption, averages and fluctuations in nuclear reactions. The fluctuations in the entrance channel result in the compound nucleus, Hauser-Feshbach, cross section, the fluctuations in the intermediate channels, result in modifications of multistep reaction cross sections, while the fluctuations in the final channel result in hybrid cross sections that can be used to describe incomplete fusion reactions. We discuss the latter in details and comment on the validity of the assumptions used in the develpoment of the Surrogate method. We also discuss the theory of multistep reactions with regards to intermediate state fluctuations and the energy dependence and non-locality of the intermediate channels optical potentials.Comment: 9 pages. Contribution to the International Workshop on Compound-Nuclear Reactions and Related Topics (CNR*2007), October 22-26, 2007, Fish Camp, California. To be published in AIP Proceedings (Editor Jutta Escher

Dispersive Gap Mode of Phonons in Anisotropic Superconductors

We estimate the effect of the superconducting gap anisotropy in the dispersive gap mode of phonons, which is observed by the neutron scattering on borocarbide superconductors. We numerically analyze the phonon spectrum considering the electron-phonon coupling, and examine contributions coming from the gap suppression and the sign change of the pairing function on the Fermi surface. When the sign of the pairing function is changed by the nesting translation, the gap mode does not appear. We also discuss the suppression of the phonon softening of the Kohn anomaly due to the onset of superconductivity. We demonstrate that observation of the gap dispersive mode is useful for sorting out the underlying superconducting pairing function.Comment: 7 pages, 12 figures, to be published in J. Phys. Soc. Jp

Separation of long DNA chains using non-uniform electric field: a numerical study

We study migration of DNA molecules through a microchannel with a series of electric traps controlled by an ac electric field. We describe the motion of DNA based on Brownian dynamics simulations of a beads-spring chain. Our simulation demonstrates that the chain captured by an electrode escapes from the binding electric field due to thermal fluctuation. We find that the mobility of chain would depend on the chain length; the mobility sharply increases when the length of a chain exceeds a critical value, which is strongly affected by the amplitude of the applied ac field. Thus we can adjust the length regime, in which this microchannel well separates DNA molecules, without changing the structure of the channel. We also present a theoretical insight into the relation between the critical chain length and the field amplitude.Comment: 12 pages, 9 figure

Neutron inelastic scattering in natural Cu as a background in neutrinoless double-beta decay experiments

Experiments designed to study rare processes, such as neutrinoless double beta decay ($0\nu\beta\beta$), are crucial tests for physics beyond the standard model. These experiments rely on reducing the intrinsic radioactive background to unprecedented levels, while adequately shielding the detectors from external sources of radioactivity. An understanding of the potential for neutron excitation of the shielding and detector materials is important for obtaining this level of sensitivity. Using the broad-spectrum neutron beam at LANSCE, we have measured inelastic neutron scattering on $^{nat}$Cu. The goal of this work is focused on understanding the background rates from neutrons interacting in these materials in regions around the Q-values of many candidate $0\nu\beta\beta$ decay isotopes, as well as providing data for benchmarking Monte Carlo simulations of background events. Results: We extracted the level cross sections from the $\gamma$ production cross section for 46 energy levels in $^{nat}$Cu . These level cross sections were compared with the available experimental data, as well as the ENDF/B-VII evaluation for discrete levels. We also examined the potential implications of our measurements on $0\nu\beta\beta$ measurements and found that many of the commonly studied $0\nu\beta\beta$ isotopes had Q-values below the cutoff for ENDF/B-VII evaluated discrete levels in either Cu nucleus.Comment: 15 pages, 18 figure

Pengaruh Penggunaan Bahan Bakar Premium, Pertamax, Pertamax Plus Dan Spiritus Terhadap Unjuk Kerja Engine Genset 4 Langkah

Peningkatan penggunaan dari bahan bakar fosil untuk keperluan alat trasportasi terus meningkat setiap harinya. Dimana bahan bakar yang digunakan berasal dari bahan bakar fosil yang tidak dapat diperbaharui, untuk itu diharapkan ada solusi mengatasi dari permasalah yang timbul akibat dari persediaan minyak bumi yang semakin lama semakin menipis. Salah satu solusi yang dapat diberikan adalah dengan menggunakan spiritus sebagai bahan bakar pengganti dari bahan bakar fosil. Penggunaan spiritus sebagai bahan bakar merupakan salah satu bahan bakar yang dapat diperbaharui. Uji coba dilakukan di laboratorium Motor Pembakaran Dalam Teknik Mesin ITS pada genset Yasuka 4 langkah dengan menggunakan bahan bakar premium, pertamax, pertamax Plus dan spiritus. Penelitian meliputi pengujian performa unjuk kerja pada engine genset 4 langkah. Pengujian dilakukan dengan menggunakan electrical dynamometer test, dengan pembebanan yang diberikan menggunakan lampu pijar dari 100 watt sampai 700 watt dengan interval 100 watt. Dari penelitian didapatkan, dengan penggunaan jenis bahan bakar spiritus mampu menghasilkan unjuk kerja dan gas buang yang baik. Perbaikan yang diperoleh pada unjuk kerja mesin yaitu daya efektik mengalami kenaikan sebesar 6,62 %, torsi mengalami kenaikan sebesar 6,61 %, tekanan efektif rata-rata mengalami kenaikan sebesar 6,61 % dan efisiensi thermal mengalami kenaikan sebesar 25,39 %. Perbaikan yang diperoleh pada emisi CO turun sebesar 174,77 % dan HC turun sebesar 254,35 %