Sensitivity Analysis of Values at Risk

The aim of this paper is to analyze the sensitivity of Value at Risk (VaR) with respect to portfolio allocation. We derive analytical expressions for the first and second derivatives of the Value at Risk, and explain how they can be used to simplify statistical inference and to perform a local analysis of the Value at Risk. An empirical illustration of such an analysis is given for a portfolio of French stocks.

Artificial pneumoperitoneum as a radio-diagnostic measure

It would appear to be fairly well established that no actual intensification of shadows on the X -ray plate need be looked for, despite the result of the experiment described on page 35 et seq., by the process of surrounding an organ with gas. What is obtained, however, by this means is a derriarcation of the edge of such an organ, where the edge would, on account of close apposition to, or overlapping with, other structures of equal or greater density, have been lost. Any value that the method possesses as, a clinica]/diagnostic measure, is dependent on this factor. We are thereby enabled :-a . To judge of the shape, contour and size of the organs • b. To locate them in cases where their position is abnormal • c. To recognise various pathological processes.The difficulties connected with the radiographic demonstration of the liver and spleen in their entirety, have hitherto almost been insuperable , and pathological conditions affecting their parietal surfaces have perforce remained obscure. Splenic enlargement needed to be very considerable in extent before indisputable evidence to that effect could be read from a skiagram. This difficulty, it may be claimed with justice, has been solved to a large extent by the method of gas inflation of the peritoneal cavity. The diagnosis of a number of pathological processes, dependant on a delineation of one or other of these organs, has been simplified.The clear picture obtained of the subphrenic space and diaphragm leads to the confident expectation of progressing the recognition of diseases of this difficult region.The claims of various American authors notwithstanding, the positive diagnosis of gall stones and gall bladder. disease would seem to have made disproportionately slow progress. The shadows of the stones , if present , tended to be so faint that they were generally lost in that of the liver, especially if the confusing effects of gas in the intestine were superadded.The viscus itself could seldom be shown on the plate, unless very markedly altered by disease.The inflation method is of undoubted value in assisting to render visible the gall bladder . Indeed it may be stated that, with proper technical precautions, the normal viscus should generally be seen on the plate . With the field thus confined by the delineation of the gall bladder, gall stones should be seen in a larger proportion of cases. Adhesions to surrounding organs,. with consequent deformation, is often recognised when present.While the method is of use in the investigation of cases in which the actual position of a kidney, difficult to make up with the ordinary method, has to be determined, it does not appear to be of much value in the demonstration of urinary calculi generally. When the kidney outline is discernible, nothing is to be gained by inflation. Neither can the ureter be shown, and the bladder is easily filled with gas per urethram, if necessary for radiographic purposes.While it is certain that the female generative organs and tumour growths in the pelvis are capable of demonstration with this method, no special advantages can be claimed for it as compared with the ordinary clinical methods of investigation of these cases.In dealing with the digestive tract also, the clinician would be better served by the use of the opaque meal method. The walls of the stomach and colon can certainly be rendered visible if these portions of the tract are separately inflated in combination with peritoneal distension, but it is open to grave doubt if any information of real value would be gained. There is no evidence to support the expectation that carcinoma of the large intestine would be rendered manifest at an earlier stage than otherwise.The scope of the usefulness of the method may be summed up as comprising :- 1. Lesions of the diaphragm, subphranic space, liver and spleen, where the zone of separation produced by the gas reveals the whole of such area or organ. • 2. Gallstones and other gall bladder lesions, in which the fact that the size and form of the viscus can be studied often provides data of great diagnostic significance. • 3. The determination of the exact position of the kidney, in doubtful cases. • 4. Abdominal tumours, the anatomical relationships of which can often be traced. • 5. Adhesions of the viscera to the parietal peritoneum.Finally, while the method is not at present recommended as a routine procedure, and its indiscriminate use in cases of intra-abdominal disease is to be deprecated, it must be conceded that it records an undoubted advance in radio -diagnosis

InP and GaAs characterization with variable stoichiometry obtained by molecular spray

Both InP and GaAs surfaces were studied in parallel. A molecular spray technique was used to obtain two semiconductor surfaces with different superficial compositions. The structures of these surfaces were examined by electron diffraction. Electron energy loss was measured spectroscopically in order to determine surface electrical characteristics. The results are used to support conclusions relative to the role of surface composition in establishing a Schottky barrier effect in semiconductor devices

Above-ground biomass and productivity in a rain forest of eastern South America

Abstract: The dynamics of tropical forest woody plants was studied at the Nouragues Field Station, central French Guiana. Stem density, basal area, above-ground biomass and above-ground net primary productivity, including the contribution of litterfall, were estimated from two large permanent census plots of 12 and 10 ha, established on contrasting soil types, and censused twice, first in 1992¿1994, then again in 2000¿2002. Mean stem density was 512 stems ha¿1 and basal area, 30m2 ha¿1. Stem mortality rate ranged between 1.51% and 2.06% y¿1. In both plots, stem density decreased over the study period. Using a correlation between wood density and wood hardness directly measured by a Pilodyn wood tester,we found that the mean wood densitywas 0.63 g cm¿3, 12% smaller than the mean of wood density estimated from the literature values for the species occurring in our plot. Above-ground biomass ranged from 356 to 398Mgha¿1 (oven-dry mass), and it increased over the census period. Leaf biomass was 6.47Mg ha¿1. Our total estimate of aboveground net primary productivity was 8.81 MgC ha¿1 y¿1 (in carbon units), not accounting for loss to herbivory, branchfalls, or biogenic volatile organic compounds, whichmay altogether account for an additional 1MgC ha¿1 y¿1. Coarse wood productivity (stem growth plus recruitment) contributed to 4.16 MgC ha¿1 y¿1. Litterfall contributed to 4.65MgC ha¿1 y¿1 with 3.16 MgC ha¿1 y¿1 due to leaves, 1.10 MgC ha¿1 y¿1 to twigs, and 0.39MgC ha¿1 y¿1 to fruits and flowers. The increase in above-ground biomass for both trees and lianas is consistentwith the hypothesis of a shift in the functioning of Amazonian rain forests driven by environmental changes, although alternative hypotheses such as a recovery from past disturbances cannot be ruled out at our site, as suggested by the observed decrease in stem density. Key Words: above-ground biomass, carbon, French Guiana, net primary productivity, tropical fores

First experimental demonstration of temporal hypertelescope operation with a laboratory prototype

In this paper, we report the first experimental demonstration of a Temporal HyperTelescope (THT). Our breadboard including 8 telescopes is firstly tested in a manual cophasing configuration on a 1D object. The Point Spread Function (PSF) is measured and exhibits a dynamics in the range of 300. A quantitative analysis of the potential biases demonstrates that this limitation is related to the residual phase fluctuation on each interferometric arm. Secondly, an unbalanced binary star is imaged demonstrating the imaging capability of THT. In addition, 2D PSF is recorded even if the telescope array is not optimized for this purpose.Comment: Accepted for publication in MNRAS. 11 pages, 25 figure

Lattice gas with ``interaction potential''

We present an extension of a simple automaton model to incorporate non-local interactions extending over a spatial range in lattice gases. {}From the viewpoint of Statistical Mechanics, the lattice gas with interaction range may serve as a prototype for non-ideal gas behavior. {}From the density fluctuations correlation function, we obtain a quantity which is identified as a potential of mean force. Equilibrium and transport properties are computed theoretically and by numerical simulations to establish the validity of the model at macroscopic scale.Comment: 12 pages LaTeX, figures available on demand ([email protected]