On the Optimal Size of a Buffer Stock -The Case of Wheat in Pakistan

In a study of the operation of the wheat market in Pakistan, Cornelisse and Naqvi [I, p. 116] stated that the pre-harvest wheat stock in March 1983 of 2,100,000 tons should provide sufficient protection against a major harvest failure. This conclusion was based on the observation that a stock of that size corresponded to approximately 40 percent of the marketed surplus of wheat and to 17 percent of domestic production - very secure proportions according to the prevailing standards. Two questions, however, remain. One, it is not yet clear what the chances are that a bad harvest or a series of bad harvests wipes out the available stock and - if that happens - what is the expected volume of wheat imports needed to supplement the stock. Two, while security is one concern in buffer stock management, the cost aspect is another. A large buffer stock provides excellent security, but it also entails high costs of storage; a smaller stock may reduce security only slightly and reduce costs considerably. On the other hand, if a buffer stock is small, the probability that supplementary imports are needed is relatively high and so is the expected volume of these imports. Considering the fact that in Pakistan domestically produced wheat is much cheaper than imported wheat, this implies that a small stock of wheat, too, may involve high costs, in this case due to imports. Thus the question arises: what is the size of the wheat buffer stock that minimizes costs

Cosmic rays studied with a hybrid high school detector array

The LORUN/NAHSA system is a pathfinder for hybrid cosmic ray research combined with education and outreach in the field of astro-particle physics. Particle detectors and radio antennae were mainly setup by students and placed on public buildings. After fully digital data acquisition, coincidence detections were selected. Three candidate events confirmed a working prototype, which can be multiplied to extend further particle detector arrays on high schools.Comment: 10 pages, 6 figures. Nigl, A., Timmermans, C., Schellart, P., Kuijpers, J., Falcke, H., Horneffer, A., de Vos, C. M., Koopman, Y., Pepping, H. J., Schoonderbeek, G., Cosmic rays studied with a hybrid high school detector array, Europhysics News (EPN), Vol. 38, No. 5, accepted on 22/08/200

Morphological variability in unrepaired bilateral clefts with and without cleft palate evaluated with geometric morphometrics

In subjects with orofacial clefts, there is an unresolved controversy on the effect of congenital maxillary growth deficiency vs. the effect of surgical intervention on the outcome of treatment. Intrinsic growth impairment in subjects with orofacial clefts can be studied by comparing facial morphology of subjects with untreated cleft and unaffected individuals of the same ethnic background. Bilateral cleft lip and palate is the most severe and least prevalent form of the orofacial cleft. The aim of this study was to compare facial morphology in subjects with unrepaired complete bilateral clefts and unaffected controls using geometric morphometrics. Lateral cephalograms of 39 Indonesian subjects with unrepaired bilateral complete cleft lip and alveolus (mean age: 24 years), or unrepaired bilateral complete cleft lip, alveolus, and palate (mean age: 20.6 years) and 50 age and ethnically matched controls without a cleft (25 males, 25 females, mean age: 21.2 years) were digitized and traced and shape variability was explored using principal component analysis, while differences between groups and genders were evaluated with canonical variate analysis. Individuals with clefts had a more pronounced premaxilla than controls. Principal component analysis showed that facial variation in subjects with clefts occurred in the anteroposterior direction, whereas in controls it was mostly in the vertical direction. Regression analysis with group, sex, and age as covariates and principal components from 1 to 6 as dependent variables demonstrated a very limited effect of the covariates on the facial shape variability (only 11.6% of the variability was explained by the model). Differences between cleft and non-cleft subjects in the direction of facial variability suggest that individuals with bilateral clefts can have an intrinsic growth impairment affecting facial morphology later in life.</p

ORFEUS II Far-UV Spectroscopy of AM Herculis

Six high-resolution (\lambda/\Delta\lambda ~ 3000) far-UV (\lambda\lambda = 910-1210 \AA) spectra of the magnetic cataclysmic variable AM Herculis were acquired in 1996 November during the flight of the ORFEUS-SPAS II mission. AM Her was in a high optical state at the time of the observations, and the spectra reveal emission lines of O VI \lambda\lambda 1032, 1038, C III \lambda 977, \lambda 1176, and He II \lambda 1085 superposed on a nearly flat continuum. Continuum flux variations can be described as per Gansicke et al. by a ~ 20 kK white dwarf with a ~ 37 kK hot spot covering a fraction f~0.15 of the surface of the white dwarf, but we caution that the expected Lyman absorption lines are not detected. The O VI emission lines have narrow and broad component structure similar to that of the optical emission lines, with radial velocities consistent with an origin in the irradiated face of the secondary and the accretion funnel, respectively. The density of the narrow- and broad-line regions is n_{nlr} ~ 3\times 10^{10} cm^{-3} and n_{blr} ~ 1\times 10^{12} cm^{-3}, respectively, yet the narrow-line region is optically thick in the O VI line and the broad-line region is optically thin; apparently, the velocity shear in the broad-line region allows the O VI photons to escape, rendering the gas effectively optically thin. Unexplained are the orbital phase variations of the emission-line fluxes.Comment: 15 pages, 6 Postscript figures; LaTeX format, uses aaspp4.sty; table2.tex included separately because it must be printed sideways - see instructions in the file; accepted on April 17, 1998 for publication in The Astrophysical Journa

Accretion physics of AM Herculis binaries, I. Results from one-dimensional stationary radiation hydrodynamics

We have solved the one-dimensional stationary two-fluid hydrodynamic equations for post-shock flows on accreting magnetic white dwarfs simultaneous with the fully frequency and angle-dependent radiative transfer for cyclotron radiation and bremsstrahlung. Magnetic field strengths B = 10 to 100 MG are considered. At given B, this theory relates the properties of the emission region to a single physical parameter, the mass flow density (or accretion rate per unit area). We present the normalized temperature profiles and fit formulae for the peak electron temperature, the geometrical shock height, and the column density of the post-shock flow. The results apply to pillbox-shaped emission regions. With a first-order temperature correction they can also be used for narrower columns provided they are not too tall.Comment: 10 pages with 10 Postscript figures, accepted for publication in Astronomy & Astrophysics. The source file contains Table 1a/b in ASCII forma

SPH Simulations of Direct Impact Accretion in the Ultracompact AM CVn Binaries

The ultracompact binary systems V407 Vul (RX J1914.4+2456) and HM Cnc (RX J0806.3+1527) - a two-member subclass of the AM CVn stars - continue to pique interest because they defy unambiguous classification. Three proposed models remain viable at this time, but none of the three is significantly more compelling than the remaining two, and all three can satisfy the observational constraints if parameters in the models are tuned. One of the three proposed models is the direct impact model of Marsh & Steeghs (2002), in which the accretion stream impacts the surface of a rapidly-rotating primary white dwarf directly but at a near-glancing angle. One requirement of this model is that the accretion stream have a high enough density to advect its specific kinetic energy below the photosphere for progressively more-thermalized emission downstream, a constraint that requires an accretion spot size of roughly 1.2x10^5 km^2 or smaller. Having at hand a smoothed particle hydrodynamics code optimized for cataclysmic variable accretion disk simulations, it was relatively straightforward for us to adapt it to calculate the footprint of the accretion stream at the nominal radius of the primary white dwarf, and thus to test this constraint of the direct impact model. We find that the mass flux at the impact spot can be approximated by a bivariate Gaussian with standard deviation \sigma_{\phi} = 164 km in the orbital plane and \sigma_{\theta} = 23 km in the perpendicular direction. The area of the the 2\sigma ellipse into which 86% of the mass flux occurs is roughly 47,400 km^2, or roughly half the size estimated by Marsh & Steeghs (2002). We discuss the necessary parameters of a simple model of the luminosity distribution in the post-impact emission region.Comment: 24 pages, 5 figures, Accepted for publication in Ap

GALEX, Optical and IR Light Curves of MQ Dra: UV Excesses at Low Accretion Rates

Ultraviolet light curves constructed from NUV and FUV detectors on GALEX reveal large amplitude variations during the orbital period of the Low Accretion Rate Polar MQ Dra (SDSSJ1553+55). This unexpected variation from a UV source is similar to that seen and discussed in the Polar EF Eri during its low state of accretion, even though the accretion rate in MQ Dra is an order of magnitude lower than even the low state of EF Eri. The similarity in phasing of the UV and optical light curves in MQ Dra imply a similar location for the source of light. We explore the possibilities of hot spots and cyclotron emission with simple models fit to the UV, optical and IR light curves of MQ Dra. To match the GALEX light curves with a single temperature circular hot spot requires different sizes of spots for the NUV and FUV, while a cyclotron model that can produce the optical harmonics with a magnetic field near 60 MG requires multipoles with fields > 200 MG to match the UV fluxes.Comment: accepted for ApJ; 15 pages, 7 tables, 8 fig

Index of Complexity, Outcome and Need scored on plaster and digital models

The aim of this study was to compare standard plaster models with their digital counterparts for the applicability of the Index of Complexity, Outcome, and Need (ICON). Generated study models of 30 randomly selected patients: 30 pre- (T0) and 30 post- (T1) treatment. Two examiners, calibrated in the ICON, scored the digital and plaster models. The overall ICON scores were evaluated for reliability and reproducibility using kappa statistics and reliability coefficients. The values for reliability of the total and weighted ICON scores were generally high for the T0 sample (range 0.83-0.95) but less high for the T1 sample (range 0.55-0.85). Differences in total ICON score between plaster and digital models resulted in mostly statistically insignificant values (P values ranging from 0.07 to 0.19), except for observer 1 in the T1 sample. No statistically different values were found for the total ICON score on either plaster or digital models. ICON scores performed on computer-based models appear to be as accurate and reliable as ICON scores on plaster model