Optimization of a Langmuir-Taylor detector for lithium

This paper describes the construction and optimization of a Langmuir-Taylor detector for lithium, using a rhenium ribbon. The absolute detection probability of this very sensitive detector is measured and the dependence of this probability with oxygen pressure and surface temperature is studied. Sources of background signal and their minimization are also discussed in details. And a comparison between our data concerning the response time of the detector and literature values is given. A theoretical analysis has been made: this analysis supports the validity of the Saha-Langmuir law to relate the ionization probability to the work function. Finally, the rapid variations of the work function with oxygen pressure and temperature are explained by a chemical equilibrium model.Comment: 11 pages, 7 figures, to appear in Rev. Sci. Instru

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

Structures and Electromagnetic Properties of New Metal-Ordered Manganites; RBaMn_{2}O_{6} (R = Y and Rare Earth Elements)

New metal-ordered manganites RBaMn_{2}O_{6} have been synthesized and investigated in the structures and electromagnetic properties. RBaMn_{2}O_{6} can be classified into three groups from the structural and electromagnetic properties. The first group (R = La, Pr and Nd) has a metallic ferromagnetic transition, followed by an A-type antiferromagnetic transition in PrBaMn_{2}O_{6}. The second group (R = Sm, Eu and Gd) exhibits a charge-order transition, followed by an antiferromagnetic long range ordering. The third group (R = Tb, Dy and Ho) shows successive three phase transitions, the structural, charge/orbital-order and magnetic transitions, as observed in YBaMn_{2}O_{6}. Comparing to the metal-disordered manganites (R^{3+}_{0.5}A^{2+}_{0.5})MnO_{3}, two remarkable features can be recognized in RBaMn_{2}O_{6}; (1) relatively high charge-order transition temperature and (2) the presence of structural transition above the charge-order temperature in the third group. We propose a possible orbital ordering at the structural transition, that is a possible freezing of the orbital, charge and spin degrees of freedom at the independent temperatures in the third group. These features are closely related to the peculiar structure that the MnO_{2} square-lattice is sandwiched by the rock-salt layers of two kinds, RO and BaO with extremely different lattice-sizes.Comment: 5 pages, 4 figures, submitted to J. Phys. Soc. Jp

Studi Eksperimen Distribusi Temperatur Nyala Api Kompor Bioetanol Tipe Side Burner Dengan Variasi Diameter Firewall

Untuk mendapatkan kompor bioetanol efisiensi thermal maksimal diperlukan penelitian komprehensif. Salah satunya adalah penelitian terhadap posisi peletakkan beban pada kompor bioetanol kompak. Pengujian dilakukan pada kompor uji bioetanol dengan kadar 99%, yaitu kompor bioetanol tipe side burner dengan firewall 2.5 inci dan firewall 3 inci. Pengukuran temperatur api dengan 13 thermocouple K dengan pengukuran searah api keatas setiap 5 mm-an. Kemudian, water boiling test dilakukan untuk mendapatkan daya dan beban dan dilanjutkan mengukur waktu pendidihan air. Hasil penelitian ini menunjukkan gambaran total distribusi temperatur nyala api difusi. Hasil menunjukkan untuk kompor 2.5 inci dengan daya 1.6 kW mempunyai temperatur 542 ºC dengan jarak ketinggian 5 mm dari rim kompor sedangkan kompor 3 inci menghasilkan daya 2.38 kW dengan temperatur 516 ºC

Revisiting Nucleosynthesis Constraints on Primordial Magnetic Fields

In view of several conflicting results, we reanalyze the effects of magnetic fields on the primordial nucleosynthesis. In the case the magnetic field is homogeneous over a horizon volume, we show that the main effects of the magnetic field are given by the contribution of its energy density to the Universe expansion rate and the effect of the field on the electrons quantum statistics. Although, in order to get an upper limit on the field strength, the weight of the former effect is numerically larger, the latter cannot be neglected. Including both effects in the PN code we get the upper limit $B \le 1\times 10^{11}$ Gauss at the temperature $T = 10^9~^oK$. We generalize the considerations to cases when instead the magnetic is inhomogeneous on the horizon length. We show that in these cases only the effect of the magnetic field on the electrons statistics is relevant. If the coherence length of the magnetic field at the end of the PN is in the range $10 \ll L_0 \ll 10^{11}$ cm our upper limit is $B \le 1\times 10^{12}$ Gauss.Comment: 12 pages LaTex file with two included ps fig

Terminal velocity and drag reduction measurements on superhydrophobic spheres

Super water-repellent surfaces occur naturally on plants and aquatic insects and are created in the laboratory by combining micro- or nanoscale surface topographic features with hydrophobic surface chemistry. When such types of water-repellent surfaces are submerged they can retain a film of air (a plastron). In this work, we report measurements of the terminal velocity of solid acrylic spheres with various surface treatments settling under the action of gravity in water. We observed increases in terminal velocity corresponding to drag reduction of between 5% and 15% for superhydrophobic surfaces that carry plastrons

Charge oscillation-induced light transmission through subwavelength slits and holes

We present a concrete picture of spoof surface plasmons (SSPs) combined with cavity resonance to clarify the basic mechanism underlying extraordinary light transmission through metal films with subwavelength slits or holes. This picture may indicate a general mechanism of metallic nanostructure optics: When light is incident on a non-planar conducting surface, the free electrons cannot move homogeneously in response to the incident electric field, i.e., their movement can be impeded at the rough parts, forming inhomogeneous charge distributions. The oscillating charges/dipoles then emit photons (similar to Thomson scattering of x rays by oscillating electrons), and the interference between the photons may give rise to anomalous transmission, reflection or scattering.Comment: 4 pages, 4 figures, are "surface plasmons" true for conducting structures? Answere is here. Also see the new arXiv:0903.3565v1, the expansion of this pape