Initial Observations of Sunspot Oscillations Excited by Solar Flare

Observations of a large solar flare of December 13, 2006, using Solar Optical Telescope (SOT) on Hinode spacecraft revealed high-frequency oscillations excited by the flare in the sunspot chromosphere. These oscillations are observed in the region of strong magnetic field of the sunspot umbra, and may provide a new diagnostic tool for probing the structure of sunspots and understanding physical processes in solar flares.Comment: 10 pages, 6 figures, ApJL in pres

Rotating Stars and the Formation of Bipolar Planetary Nebulae II: Tidal Spin-up

We present new binary stellar evolution models that include the effects of tidal forces, rotation, and magnetic torques with the goal of testing Planetary Nebulae (PNe) shaping via binary interaction. We explore whether tidal interaction with a companion can spin up the AGB envelope. To do so we have selected binary systems with main sequence masses of 2.5 \Mo and of 0.8 \Mo and evolve them allowing initial separations of 5, 6, 7, and 8 AU. The binary stellar evolution models have been computed all the way to the PNe formation phase or until Roche lobe overflow (RLOF) is reached, whatever happens first. We show that with initial separations of 7 and 8 AU, the binary avoids entering into RLOF, and the AGB star reaches moderate rotational velocities at the surface ($\sim 3.5$ and $\sim 2$ \kms respectively) during the inter-pulse phases, but after the thermal pulses it drops to a final rotational velocity of only $\sim 0.03$ \kms. For the closest binary separations explored, 5 and 6 AU, the AGB star reaches rotational velocities of $\sim 6$ and $\sim 4$ \kms respectively when the RLOF is initiated. We conclude that the detached binary models that avoid entering the RLOF phase during the AGB will not shape bipolar PNe, since the acquired angular momentum is lost via the wind during the last two thermal pulses. This study rules out tidal spin-up in non-contact binaries as a sufficient condition to form bipolar PNe.Comment: 25 pages, 3 figures, accepted by The Astrophysical Journa

Dynamic model for failures in biological systems

A dynamic model for failures in biological organisms is proposed and studied both analytically and numerically. Each cell in the organism becomes dead under sufficiently strong stress, and is then allowed to be healed with some probability. It is found that unlike the case of no healing, the organism in general does not completely break down even in the presence of noise. Revealed is the characteristic time evolution that the system tends to resist the stress longer than the system without healing, followed by sudden breakdown with some fraction of cells surviving. When the noise is weak, the critical stress beyond which the system breaks down increases rapidly as the healing parameter is raised from zero, indicative of the importance of healing in biological systems.Comment: To appear in Europhys. Let

What is the evidence of the impact of microfinance on the well-being of poor people?

The concept of microcredit was first introduced in Bangladesh by Nobel Peace Prize winner Muhammad Yunus. Professor Yunus started Grameen Bank (GB) more than 30 years ago with the aim of reducing poverty by providing small loans to the country’s rural poor (Yunus 1999). Microcredit has evolved over the years and does not only provide credit to the poor, but also now spans a myriad of other services including savings, insurance, remittances and non-financial services such as financial literacy training and skills development programmes; microcredit is now referred to as microfinance (Armendáriz de Aghion and Morduch 2005, 2010). A key feature of microfinance has been the targeting of women on the grounds that, compared to men, they perform better as clients of microfinance institutions and that their participation has more desirable development outcomes (Pitt and Khandker 1998). Despite the apparent success and popularity of microfinance, no clear evidence yet exists that microfinance programmes have positive impacts (Armendáriz de Aghion and Morduch 2005, 2010; and many others). There have been four major reviews examining impacts of microfinance (Sebstad and Chen, 1996; Gaile and Foster 1996, Goldberg 2005, Odell 2010, see also Orso 2011). These reviews concluded that, while anecdotes and other inspiring stories (such as Todd 1996) purported to show that microfinance can make a real difference in the lives of those served, rigorous quantitative evidence on the nature, magnitude and balance of microfinance impact is still scarce and inconclusive (Armendáriz de Aghion and Morduch 2005, 2010). Overall, it is widely acknowledged that no well-known study robustly shows any strong impacts of microfinance (Armendáriz de Aghion and Morduch 2005, p199-230). Because of the growth of the microfinance industry and the attention the sector has received from policy makers, donors and private investors in recent years, existing microfinance impact evaluations need to be re-investigated; the robustness of claims that microfinance successfully alleviates poverty and empowers women must be scrutinised more carefully. Hence, this review revisits the evidence of microfinance evaluations focusing on the technical challenges of conducting rigorous microfinance impact evaluations

Off-diagonal magnetoimpedance in field-annealed Co-based amorphous ribbons

The off-diagonal magnetoimpedance in field-annealed CoFeSiB amorphous ribbons was measured in the low-frequency range using a pick-up coil wound around the sample. The asymmetric two-peak behavior of the field dependence of the off-diagonal impedance was observed. The asymmetry is attributed to the formation of a hard magnetic crystalline phase at the ribbon surface. The experimental results are interpreted in terms of the surface impedance tensor. It is assumed that the ribbon consists of an inner amorphous region and surface crystalline layers. The coupling between the crystalline and amorphous phases is described through an effective bias field. A qualitative agreement between the calculated dependences and experimental data is demonstrated. The results obtained may be useful for development of weak magnetic-field sensors.Comment: 19 pages, 6 figure

Magnetoelectric Effects on Composite Nano Granular Fe/TiO2−δFe/TiO_{2-\delta} Films

Employing a new experimental technique to measure magnetoelectric response functions, we have measured the magnetoelectric effect in composite films of nano granular metallic iron in anatase titanium dioxide at temperatures below 50 K. A magnetoelectric resistance is defined as the ratio of a transverse voltage to bias current as a function of the magnetic field. In contrast to the anomalous Hall resistance measured above 50 K, the magnetoelectic resistance below 50 K is significantly larger and exhibits an even symmetry with respect to magnetic field reversal $H\to -H$. The measurement technique required attached electrodes in the plane of the film composite in order to measure voltage as a function of bias current and external magnetic field. To our knowledge, the composite films are unique in terms of showing magnetoelectric effects at low temperatures, $<$ 50 K, and anomalous Hall effects at high temperatures, $>$ 50 K.Comment: ReVTeX, 2 figures, 3 page

Electronic Transport in the Oxygen Deficient Ferromagnetic Semiconducting TiO2−δ_{2-\delta}

TiO$_{2-\delta}$ films were deposited on (100) Lanthanum aluminates LaAlO$_{3}$ substrates at a very low oxygen chamber pressure $P\approx 0.3$ mtorr employing a pulsed laser ablation deposition technique. In previous work, it was established that the oxygen deficiency in these films induced ferromagnetism. In this work it is demonstrated that this same oxygen deficiency also gives rise to semiconductor titanium ion impurity donor energy levels. Transport resistivity measurements in thin films of TiO$_{2-\delta}$ are presented as a function of temperature and magnetic field. Magneto- and Hall- resistivity is explained in terms of electronic excitations from the titanium ion donor levels into the conduction band.Comment: RevTeX4, Four pages, Four Figures in ^.eps forma