4,580 research outputs found
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 ÂșC dengan jarak ketinggian 5 mm dari rim kompor sedangkan kompor 3 inci menghasilkan daya 2.38 kW dengan temperatur 516 ÂșC
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 Gauss at the temperature . 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 cm
our upper limit is 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
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