Developmental sensory experience balances cortical excitation and inhibition.

Early in life, neural circuits are highly susceptible to outside influences. The organization of the primary auditory cortex (A1) in particular is governed by acoustic experience during the critical period, an epoch near the beginning of postnatal development throughout which cortical synapses and networks are especially plastic. This neonatal sensitivity to the pattern of sensory inputs is believed to be essential for constructing stable and adequately adapted representations of the auditory world and for the acquisition of language skills by children. One important principle of synaptic organization in mature brains is the balance between excitation and inhibition, which controls receptive field structure and spatiotemporal flow of neural activity, but it is unknown how and when this excitatory-inhibitory balance is initially established and calibrated. Here we use whole-cell recording to determine the processes underlying the development of synaptic receptive fields in rat A1. We find that, immediately after the onset of hearing, sensory-evoked excitatory and inhibitory responses are equally strong, although inhibition is less stimulus-selective and mismatched with excitation. However, during the third week of postnatal development, excitation and inhibition become highly correlated. Patterned sensory stimulation drives coordinated synaptic changes across receptive fields, rapidly improves excitatory-inhibitory coupling and prevents further exposure-induced modifications. Thus, the pace of cortical synaptic receptive field development is set by progressive, experience-dependent refinement of intracortical inhibition

BANCOSOL: THE CHALLENGE OF GROWTH FOR MICROFINANCE ORGANIZATIONS

This paper focuses on the difficulties inherent in the prudent management of growth of microfinance organizations and on potential limits to the increased efficiency, profitability, and sustainability expected from growth and large size. The paper addresses both positive and negative implications of rapid growth for microfinance organizations. The experience of BancoSol in Bolivia is used to illustrate these questions. Building upon the successful experience of PRODEM, BancoSol was chartered as a private commercial bank in 1992. The paper discusses the intangible assets inherited from PRODEM that gave BancoSol a head start and the additional advantages that resulted from formalization as a bank, in particular from the authorization to mobilize deposits. BancoSol shows outstanding success in terms of breadth, depth, and quality of outreach and in terms of sustainability. It is the microfinance organization with the largest number of clients in Latin America and it reaches poor clients who could never expect to gain access to conventional financial institutions. The paper discusses the incentive structure associated with a lending technology that has resulted in low loan arrears and the cost- effective supply of small loans. Success is explained by a strong concern with financial viability, development of a lending technology appropriate for the market niche, a long learning period, and upgrading into a formal intermediary. As it grew, BancoSol had to face a reduction of revenues as a proportion of productive assets and an increase in the average cost of funds, which combined reduced its operating margin by 13 percentage points. This challenge was fully met by reducing operating expenses as a proportion of productive assets. While growth of PRODEM had been mostly constrained by too rigid access to donor funds, growth of BancoSol has been constrained by threats on asset quality and by diminishing marginal economies of size. Portfolio efficiency has grown steadily. This growth has been the net outcome, however, of reductions in transactions efficiency and of increases in average loan size after transformation into BancoSol. The paper explores the sources of increases in average loan size and it concludes that mission drift has not occurred at BancoSol, which continues to focus on small loans to microentrepreneurs. The evolution in transactions efficiency is related, in turn, to sources of extensive (installed capacity) and intensive (productivity) growth. Extensive growth has been rapid at BancoSol and it tends to dampen productivity increases. Finally, the paper reviews the pressures from growth on the original informal culture of the organization and the gradual establishment of more formal structures.Agricultural Finance,

MICROCREDIT AND THE POOREST OF THE POOR: THEORY AND EVIDENCE FROM BOLIVIA

We construct a theoretical framework that puts the social worth of a microfinance organization (MFO) in terms of the depth, worth to users, cost to users, breadth, length, and scope of its output. We then analyze evidence of depth of outreach for five MFOs in Bolivia. Most of the poor households reached by the MFOs were near the poverty line�they were the richest of the poor. Group lenders had more depth of outreach than individual lenders. The urban poorest were more likely to be borrowers, but rural borrowers were more likely to be among the poorest.Financial Economics, Food Security and Poverty,

Microfinance Market Niches and Client Profiles in Bolivia

This paper presents and interprets descriptive statistics generated from data obtained in a survey of clients of five microfinance organizations believed to be among the best in Bolivia. These lenders represent different combinations of organizational design, lending technology, and market area of operations. Two are regulated financial intermediaries and three are NGOs. Two operate in rural areas (PRODEM and Sartawi) and three operate in urban areas (BancoSol, FIE, and Caja Los Andes). Two offer individual loans and three grant loans through joint liability groups. The paper discusses household-enterprise profiles of a sample of 622 clients and identifies terms and conditions of loan contracts with these organizations to evaluate the depth and quality of their outreach.Marketing,segmentation,Bolivia,competition,microfinance

MICROFINANCE MARKET NICHES AND CLIENT PROFILES IN BOLIVIA

This paper presents and interprets descriptive statistics generated from data obtained in a survey of clients of five microfinance organizations believed to be among the best in Bolivia. These lenders represent different combinations of organizational design, lending technology, and market area of operations. Two are regulated financial intermediaries and three are NGOs. Two operate in rural areas (PRODEM and Sartawi) and three operate in urban areas (BancoSol, FIE, and Caja Los Andes). Two offer individual loans and three grant loans through joint liability groups. The paper discusses household-enterprise profiles of a sample of 622 clients and identifies terms and conditions of loan contracts with these organizations to evaluate the depth and quality of their outreach. The interpretation seeks to establish connections between key characteristics of the clients and features of the lending technologies that lead to the matching of classes of borrowers with particular organizations and that influence the choice of market niches. Data on loan sizes suggest the existence of different but broadly overlapping market niches associated with three tiers of clients. The sharpest distinction is between urban and rural clients. The matching between clients and organizations also reflects a weak but positive correlation between levels of poverty and loan sizes. According to an index of basic needs fulfillment of their clients, these organizations can be ranked as: FIE and Caja Los Andes (first tier), BancoSol (second tier), and PRODEM and Sartawi (third tier). The same ranking is obtained when clients are ordered according to loan size, the ratio of loan size to the value of sales, and the value of monthly sales. The three tiers of clients are associated with different socio-economic features of their household-enterprises: sex, education, household size, access to electricity, water supplies, and sewage facilities, employment-generating capacity of the enterprise, informality and separation of household and enterprise, occupations and the like. The development of lending technologies that do not rely on standard financial statements and collateralizable assets is a formidable innovation that explains the outreach and sustainability of these organizations. Differences in the guarantees required for loans dominate distinctions in lending technology. Trade-offs between loan size, interest rates, and guarantee requirements attract different subsets of the clientele. Joint liability seems to be appropriate for very poor people, but group borrowers eventually outgrow this relationship. Caja Los Andes and FIE have shown that it is possible to supply individual loans to poor people and be profitable. Most clients are satisfied with the services received. The lowest satisfaction concerns loan sizes and loan-size rationing may be widespread. At least in urban areas, increasing competition will force these organizations to improve their services and adjust loan sizes. All of these organizations are expanding the frontier of microfinance by developing lending technologies for a much poorer clientele than is reached by collateral-based lenders. This is a formidable achievement.Financial Economics,

Lepton Polarization in Neutrino-Nucleon Interactions

We derive generic formulas for the polarization density matrix of leptons produced in neutrino and antineutrino collisions and briefly consider some important particular cases. Next we employ the general formalism in order to include the final lepton mass and spin into the popular model by Rein and Sehgal for single pion neutrinoproduction.Comment: Talk given at 10th International Workshop on High-Energy Spin Physics (SPIN 03), Dubna, Russia, 16-20 Sep 2003. 12 pages; extended version, typos remove

Stereochemical errors and their implications for molecular dynamics simulations

<p>Abstract</p> <p>Background</p> <p>Biological molecules are often asymmetric with respect to stereochemistry, and correct stereochemistry is essential to their function. Molecular dynamics simulations of biomolecules have increasingly become an integral part of biophysical research. However, stereochemical errors in biomolecular structures can have a dramatic impact on the results of simulations.</p> <p>Results</p> <p>Here we illustrate the effects that chirality and peptide bond configuration flips may have on the secondary structure of proteins throughout a simulation. We also analyze the most common sources of stereochemical errors in biomolecular structures and present software tools to identify, correct, and prevent stereochemical errors in molecular dynamics simulations of biomolecules.</p> <p>Conclusions</p> <p>Use of the tools presented here should become a standard step in the preparation of biomolecular simulations and in the generation of predicted structural models for proteins and nucleic acids.</p

Charged current weak production of the Delta resonance

The charge changing weak production of Delta in nucleons and nuclei is studied. The reactions e^{-} p -> Delta^{0} \nu_{e} and e^{+} p -> Delta^{++} \bar{\nu}_{e} are considered as a possible source of information about the weak N-Delta transition form factors. The low q^2 BNL data on neutrino production of Delta are used to extract the axial vector N-Delta coupling, taking into account the deuteron structure and the Delta width. Finally, pion production induced by neutrinos in ^{16}O in the Delta region, relevant to atmospheric neutrino experiments, is investigated.Comment: 4 pages, 2 figures. To appear in Proceedings of PANIC9