Bi-quadratic magnetoelectric coupling in underdoped La_2CuO_{4+x}

The recent discovery of relaxor ferroelectricity and magnetoelectric effect in lightly doped cuprate material La_2CuO_{4+x} has provided a number of questions concerning its theoretical description. It has been argued using a Ginzburg-Landau free energy approach that the magnetoelectric effect can be explained by the presence of bi-quadratic interaction terms in the free energy. Here, by using the same free energy functional, we study the variety of behavior which can emerge in the electric polarization under an external magnetic field. Subsequently, we discuss the role of Dzyaloshinskii-Moriya interaction in generating this magnetoelectric response. This work is particularly relevant for such relaxor systems where the material-dependent parameters would be affected by changes in e.g. chemical doping or cooling rate.Comment: 8 pages, 2 figures. arXiv admin note: text overlap with arXiv:1112.152

Comment on "Strong dependence of the interlayer coupling on the hole mobility in antiferromagnetic La2−x_{2-x}Srx_xCuO4_4 (x<0.02x<0.02)"

Using the experimental data given in Phys. Rev. B70, 220507 (2004), we show that -- unlike the effective coupling discussed in this paper -- the net average antiferromagnetic interlayer coupling in doped lanthanum cuprates depends only weakly on the doping or on the temperature. We argue that the effective coupling is proportional to the square of the staggered magnetization, and does not supply new information about the origin of the suppression of the magnetic order in doped samples. Our analysis is based on a modified version of the equation describing the spin-flip transition, which takes into account the decrease of the staggered moment with temperature and doping.Comment: Phys. Rev. B (in press

Economic Valuation of Urban Informal Activities: Case Study of Flea Markets in Bandung Municipality

This study analyzes some social economic aspects of informal activities using case study of flea markets in Bandung Municipality. The objectives are to provide a description of the information we collected during our field survey, and report our findings on the Willingness to Pay (WTP) of people who are doing informal business in the flea markets under study on some services. We use Censored Regression Model to estimate WTP for some relevant services (general user charge, waste disposal services, security, and congestion) in the flea market. We found two important determinants of WTP, which are the amount of working capital, and the ownership of the merchandise.Flea market, informal activity, WTP

The Impact of Microfinance on Micro and Small Enterprise’s Performance and the Improvement of Their Business Opportunity

This study finds that microfinance has positive impact to improvement of MSE’s ferformance indicated by sales; the difference in regional characteristic of MSE is also play role in determining its business scale. Since doubling amount of loan has negative impact to the performance, it’s very important to allocate the loan to the productive activities, such as investment, to improve the business opportunity.microfinance, small and medium enterprises

Maxwell's Fishpond

Most of us will have at some time thrown a pebble into water, and watched the ripples spread outwards and fade away. But now there is a way to reverse the process, and make those ripples turn around and reconverge again, ... and again, and again. To do this we have designed the Maxwell's Fishpond, a water wave or "Transformation Aquatics" version of the Maxwell's Fisheye lens [Tyc et al. 2011, Luneberg 1964] that is now well-known from transformation optics. These are transformation devices where wave propagation on the surface of a sphere is not modelled on an actual sphere, but in a flat device with carefully designed spatially varying properties. And just as for rays from a point source on a sphere, a wave disturbance in a Maxwell's Fisheye or Fishpond spreads out at first, but then reforms itself at its opposing point in the device. Here we show how such a device can be made for water waves, partly in friendly competition with comparable electromagnetic devices [Ma et al. 2011] and partly as an accessible and fun demonstration of the power of transformation mechanics. To the eye, our Maxwell's Fishpond was capable of reforming a disturbance up to five times, although such a feat required taking considerable care, close observation, and a little luck. What can you see in the video at http://www.qols.ph.ic.ac.uk/~kinsle/files/MFishpond/ ?Comment: 9 pages (v2 add links, improve fig.3, minor corrections, v3 add journal info

A STUDY OF CONSUMER SATISFACTION TOWARDS RESTAURANTS’ SERVICE QUALITY IN SURABAYA

The restaurant industry in Surabaya has shown rapid growth recently. This requires the restaurant businesses to recognize their competitive advantages in order to win the competition. One of the competitive advantages is a good service quality that will create consumer’s satisfaction. This research is aimed to know the consumer’s satisfaction towards service quality of restaurants in Surabaya and to identify if there is significant satisfaction differences based on consumer’s demographic which are gender, age, occupation, level of education and level of income. The consumers of eleven upscale restaurants in Surabaya, Indonesia were surveyed to define their expectation and perception towards the service quality of the restaurants that they experienced based on the SERVQUAL model. SERVQUAL model has five dimensions such as tangible, responsiveness, reliability, assurance and empathy. The questionnaires used were five point Likert type scales which were distributed to 553 consumers who were dine-in by using convenience and quota sampling technique. The quota for each restaurant is 50 questionnaires. The method of analysis used were descriptive statistics, customer satisfaction index, independent sample t-test and one-way ANOVA. The result shows that empathy has the biggest customer satisfaction index, 0.9714, compared to the other dimensions. It means that consumers are satisfied that the restaurant’s staffs are helpful and give personal attention to the consumers. Assurance has the lowest customer satisfaction index, 0.9332. It can be said that the consumers are satisfied that the staffs have good product knowledge, able to handle complaint and courteous to the consumers. Overall, customer satisfaction index is 0.9610 that means consumers are satisfied to the service quality that the restaurants in Surabaya have. In addition, there is no significant satisfaction differences for the consumers with different age group, different level of education and different level of income; there is only significant satisfaction differences for the consumers of different gender, that is men are more satisfied than women, and different occupation, that is civil servants are more satisfied than other occupations

Frustration of the interlayer coupling by mobile holes in La2-xSrxCuO4 (x<0.02)

We have studied the interlayer coupling in the antiferromagnetic (AF) phase of Sr and Zn doped La2CuO4 by analyzing the spin flip transition in the magnetization curves. We find that the interlayer coupling strongly depends on the mobility of the hole charge carriers. Samples with the same hole content as well as the same Neel temperature but a different hole mobility, which we adjusted by Zn co-doping, can have a very different interlayer coupling. Our results suggest that only mobile holes can cause a strong frustration of the interlayer coupling.Comment: 4 pages, 4 figure

Spin-flop transitions and spin-wave gaps in La_2CuO_4

We study the spin-wave spectrum and the spin-flop transitions in La_2CuO_4 in a uniform magnetic field at zero temperature. Using the non-linear sigma-model, we show that a field applied along the orthorhombic b direction leads to a two-step rotation of the staggered magnetization, first in the bc and then in the ac plane, until the order parameter is completely aligned along the c axis. In contrast, for a perpendicular magnetic field, we find a conventional spin-flop transition induced by the competition between the field and the interlayer coupling. A comparison with recent measurements of the field-dependence of the in-plane spin-wave gap shows a beautiful agreement between theory and experiments.Comment: 7 pages, 3 figures; added referenc