Optical characterization of the silicon photodiodes for the establishment of national radiometric standards

Optical properties of the silicon photodiodes are investigated in the visible spectral regime. Non-linearity measurement standard was established by using Hamamatsu S1337-11 type windowless silicon photodiode whose non-linearity value was found to be better than 6×10⁻⁵ at photocurrent level of 10⁻⁹ to 10⁻⁴ A. Temperature effects on the spectral responsivity for S1337-11, S1337-1010BQ and S1227-1010BQ type photodiodes were analyzed between 20°C and 40°C at 488.1, 514.7 and 632.8 nm vacuum wavelengths. The spatial uniformities of the responsivity for three type photodiodes are performed with a laser beam having 1 mm diameter by using home made two-axis micro translation system. Results of the reflectance measurements for three elements of reflection-based trap detectors were compared with the predicted values obtained from Fresnel equations.     

<Emphasis Type="Italic">N</Emphasis>-shaped voltage-current characteristic and current oscillations in Sm<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> Sr<Subscript>x</Subscript>MnO<Subscript>3</Subscript> manganite

The voltage-current characteristics (VCC) of Sm_1?xSr_x MnO₃ samples with x=0.425 and x=0.450 were experimentally studied at a temperature of 77 K in pulsed and constant electric (E) and magnetic (H) fields up to 10 kOe for the H‖E and H⊥E orientations. N-shaped VCCs and high-frequency (up to 3 MHz) current oscillations were observed. It was found that the effect of colossal magnetoresistance had a threshold character and was smoothly reduced to zero with E→0.     

Representability of Analytic Functions in Terms of Their Boundary Values

Suppose that is an arbitrary finite complex Borel measure on the interval is its Poisson integral, and are the conjugate harmonics of , and is the nontangential limiting value of the analytic function as . In this paper, we consider the problem of representing the analytic function in terms of its boundary values .     

Investigations into the Molecular Relaxation Processes in Lithium and Sodium Perchlorates by the Raman Scattering Method

The molecular relaxation processes in crystalline lithium and sodium perchlorates are investigated in the region of totally symmetric ₁(A) ClO₄ ^–-anion oscillations by Raman light scattering spectroscopy. It is demonstrated that the reorientation in LiClO₄ and NaClO₄ represents an activation process. A premelting phase is detected for sodium perchlorate.     

Kinetic effects in manganites La1 − x Ag y MnO3 (y ≤ x)

We have measured the resistivity, magnetoresistance, and thermopower of ceramic manganite samples La_{1 ? x} Ag _y MnO₃ (y ≤ x) doped with silver as functions of temperature (4.2–350 K) and magnetic field (up to 26 kOe). A metal-insulator phase transition is observed in all investigated samples at temperatures close to room temperature. The behavior of the resistivity and thermopower in the high-temperature paramagnetic region is interpreted using the concept of small radius polaron; the activation energy decreases with increasing doping level. The resistivity in the low-temperature ferromagnetic region is approximated by the expression ρ_FM(T) = ρ₀ + AT ² + BT ^4.5 presuming the existence of electron-electron and electron-magnon interactions. A resistivity minimum and a strong magnetoresistive effect are observed at low temperatures. The latter effect is associated with scattering of charge carriers at grain boundaries, which are antiferromagnetically ordered relative to one another. The temperature dependence of thermopower in the magnetically ordered phase is described in the framework of a model taking into account the drag of charge carriers by magnons.     

Double-lepton polarization asymmetries in Λ<Subscript>b</Subscript>→Λℓ<Superscript>+</Superscript>ℓ<Superscript>-</Superscript> decay in universal extra dimension model

Double-lepton polarization asymmetries in Λ_b→Λℓ⁺ℓ^- decay are calculated in the universal extra dimension (UED) model. It is found that numerous double-lepton polarization asymmetries are very sensitive to the UED model and therefore can be a very useful tool for establishing new physics predicted by the UED model. PACS 12.60.-i; 13.30.-a; 14.20.Mr     

Constructing rational and multi‐wave solutions to higher order NEEs via the Exp‐function method

In this paper, we present an application of some known generalizations of the Exp‐function method to the fifth‐order Burgers and to the seventh‐order Korteweg de Vries equations for the first time. The two examples show that the Exp‐function method can be an effective alternative tool for explicitly constructing rational and multi‐wave solutions with arbitrary parameters to higher order nonlinear evolution equations. Being straightforward and concise, as pointed out previously, this procedure does not require the bilinear representation of the equation considered. Copyright © 2011 John Wiley & Sons, Ltd.     

Shot noise in magnetic tunnel junctions: evidence for sequential tunneling

We report the experimental observation of sub-Poissonian shot noise in single magnetic tunnel junctions, indicating the importance of tunneling via impurity levels inside the tunnel barrier. For junctions with weak zero-bias anomaly in conductance, the Fano factor (normalized shot noise) depends on the magnetic configuration being enhanced for antiparallel alignment of the ferromagnetic electrodes. We propose a model of sequential tunneling through nonmagnetic and paramagnetic impurity levels inside the tunnel barrier to qualitatively explain the observations.