Credit Access: Implications for Sole-Proprietor Household Production

The objective of this study is to explain the determinants of farm and non-farm sole proprietorship households access to credit as well as the extent their credit constraints impact their value of production. A propensity, kernel-based matching estimator was employed to provide unbiased estimates of the production impacts of being denied credit. Prior research efforts have used inferior methods, including the two-stage Heckman estimator deal with estimation issues (selection bias and endogeneity) inherent in determining impacts of credit access and use. Results suggest that credit constrained sole-proprietorships, farm and non-farm, have a significantly lower value of production, but this drop in production, when aggregated to a national level, is small.farm credit, credit constraint, debt, Agricultural Finance,

Family Violence and Children’s Behavior Problems: Independent Contributions of Intimate Partner and Child-Directed Physical Aggression

Using data from a diverse sample of 581 families living in predominantly low-income, rural communities, the current study sought to investigate the longitudinal associations among father-perpetrated intimate partner violence (IPV) and child-directed physical aggression perpetrated by the mother. The unique contributions of each of these types of family violence on children’s behavioral problems at school entry were also examined. Results confirm bidirectional associations between father-perpetrated IPV and maternal physical aggression directed toward the child, and indicate that both types of physical aggression contribute to child behavior problems at school entry

The position of graptolites within Lower Palaeozoic planktic ecosystems.

An integrated approach has been used to assess the palaeoecology of graptolites both as a discrete group and also as a part of the biota present within Ordovician and Silurian planktic realms. Study of the functional morphology of graptolites and comparisons with recent ecological analogues demonstrates that graptolites most probably filled a variety of niches as primary consumers, with modes of life related to the colony morphotype. Graptolite coloniality was extremely ordered, lacking any close morphological analogues in Recent faunas. To obtain maximum functional efficiency, graptolites would have needed varying degrees of coordinated automobility. A change in lifestyle related to ontogenetic changes was prevalent within many graptolite groups. Differing lifestyle was reflected by differing reproductive strategies, with synrhabdosomes most likely being a method for rapid asexual reproduction. Direct evidence in the form of graptolithophage 'coprolitic' bodies, as well as indirect evidence in the form of probable defensive adaptations, indicate that graptolites comprised a food item for a variety of predators. Graptolites were also hosts to a variety of parasitic organisms and provided an important nutrient source for scavenging organisms

Heterostructures for Optical Devices

Contains research objectives and reports on eight research projects.Joint Services Electronics Program (Contract DAAL03-86-K-0002)Joint Services Electronics Program (Contract DAALO3-89-C-0001)National Science Foundation (Grant EET 87-03404)Charles Stark Draper Laboratory (Contract DL-H-315251)Xerox Corporation FellowshipMIT Fund

Crystallization by particle attachment in synthetic, biogenic, and geologic environments.

Field and laboratory observations show that crystals commonly form by the addition and attachment of particles that range from multi-ion complexes to fully formed nanoparticles. The particles involved in these nonclassical pathways to crystallization are diverse, in contrast to classical models that consider only the addition of monomeric chemical species. We review progress toward understanding crystal growth by particle-attachment processes and show that multiple pathways result from the interplay of free-energy landscapes and reaction dynamics. Much remains unknown about the fundamental aspects, particularly the relationships between solution structure, interfacial forces, and particle motion. Developing a predictive description that connects molecular details to ensemble behavior will require revisiting long-standing interpretations of crystal formation in synthetic systems, biominerals, and patterns of mineralization in natural environments

The laser-hybrid accelerator for radiobiological applications

The `Laser-hybrid Accelerator for Radiobiological Applications', LhARA, is conceived as a novel, uniquely-flexible facility dedicated to the study of radiobiology. The technologies demonstrated in LhARA, which have wide application, will be developed to allow particle-beam therapy to be delivered in a completely new regime, combining a variety of ion species in a single treatment fraction and exploiting ultra-high dose rates. LhARA will be a hybrid accelerator system in which laser interactions drive the creation of a large flux of protons or light ions that are captured using a plasma (Gabor) lens and formed into a beam. The laser-driven source allows protons and ions to be captured at energies significantly above those that pertain in conventional facilities, thus evading the current space-charge limit on the instantaneous dose rate that can be delivered. The laser-hybrid approach, therefore, will allow the vast ``terra incognita'' of the radiobiology that determines the response of tissue to ionising radiation to be studied with protons and light ions using a wide variety of time structures, spectral distributions, and spatial configurations at instantaneous dose rates up to and significantly beyond the ultra-high dose-rate `FLASH' regime. It is proposed that LhARA be developed in two stages. In the first stage, a programme of in vitro radiobiology will be served with proton beams with energies between 10MeV and 15MeV. In stage two, the beam will be accelerated using a fixed-field accelerator (FFA). This will allow experiments to be carried out in vitro and in vivo with proton beam energies of up to 127MeV. In addition, ion beams with energies up to 33.4MeV per nucleon will be available for in vitro and in vivo experiments. This paper presents the conceptual design for LhARA and the R&D programme by which the LhARA consortium seeks to establish the facility

Superlattice Growth via MBE and Green’s Function Techniques

A model has been developed to simulate the growth of arrays consisting of a substrate on which alternating layers of quantum dots (QDs) and spacer layers are epitaxially grown. The substrate and spacer layers are modeled as an anisotropic elastic half-space, and the QDs are modeled as point inclusions buried within the half-space. In this model, the strain at the free surface of this half-space due to the buried point QDs is calculated, and a scalar measure of the strain at the surface is subsequently determined. New point QDs are placed on the surface where the previously calculated scalar strain measure is a minimum. Following available DFT results, this scalar strain measure is a weighted average of the in-plane strains. This model is constructed under the assumption that diffusional anisotropy can be neglected, and thus, the results are more in agreement with results from experiments of growth of SiGe QDs than experiments involving QDs of (In,Ga)As

Heterostructures for High Performance Devices

Contains an introduction and reports on ten research projects.Charles S. Draper Laboratory, Contract DL-H-315251Joint Services Electronics Program, Contract DAAL03-89-C-0001National Science Foundation Grant, Grant EET 87-03404MIT FundsInternational Business Machines CorporationNational Science Foundation Grant ECS 84-1317

Removal of power-line interference from the ECG: a review of the subtraction procedure

BACKGROUND: Modern biomedical amplifiers have a very high common mode rejection ratio. Nevertheless, recordings are often contaminated by residual power-line interference. Traditional analogue and digital filters are known to suppress ECG components near to the power-line frequency. Different types of digital notch filters are widely used despite their inherent contradiction: tolerable signal distortion needs a narrow frequency band, which leads to ineffective filtering in cases of larger frequency deviation of the interference. Adaptive filtering introduces unacceptable transient response time, especially after steep and large QRS complexes. Other available techniques such as Fourier transform do not work in real time. The subtraction procedure is found to cope better with this problem. METHOD: The subtraction procedure was developed some two decades ago, and almost totally eliminates power-line interference from the ECG signal. This procedure does not affect the signal frequency components around the interfering frequency. Digital filtering is applied on linear segments of the signal to remove the interference components. These interference components are stored and further subtracted from the signal wherever non-linear segments are encountered. RESULTS: Modifications of the subtraction procedure have been used in thousands of ECG instruments and computer-aided systems. Other work has extended this procedure to almost all possible cases of sampling rate and interference frequency variation. Improved structure of the on-line procedure has worked successfully regardless of the multiplicity between the sampling rate and the interference frequency. Such flexibility is due to the use of specific filter modules. CONCLUSION: The subtraction procedure has largely proved advantageous over other methods for power-line interference cancellation in ECG signals

Optics and Quantum Electronics

Contains reports on eleven research projects.National Science Foundation (Grant EET 87-00474)Joint Services Electronics Program (Contract DAALO03-86-K-O002)Charles Stark Draper Laboratory, Inc. (Grant DL-H-2854018)National Science Foundation (Grant DMR 84-18718)National Science Foundation (Grant EET 87-03404)National Science Foundation (ECS 85-52701)US Air Force - Office of Scientific Research (Contract AFOSR-85-0213)National Institutes of Health (Contract 5-RO1-GM35459)US Navy - Office of Naval Research (Contract N00014-86-K-0117