Showing papers by "Charles University in Prague published in 1993"

Checking robust nonsingularity is NP-hard

Abstract: We consider the following problem: givenk+1 square matrices with rational entries,A0,A1,...,Ak, decide ifA0+r1A1+···+rkAk is nonsingular for all possible choices of real numbersr1, ...,rk in the interval [0, 1]. We show that this question, which is closely related to the robust stability problem, is NP-hard. The proof relies on the new concept ofradius of nonsingularity of a square matrix and on the relationship between computing this radius and a graph-theoretic problem.

Range searching with efficient hierarchical cuttings

Abstract: We present an improved space/query-time tradeoff for the general simplex range searching problem, matching known lower bounds up to small polylogarithmic factors. In particular, we construct a linear-space simplex range searching data structure withO(n1?1/d) query time, which is optimal ford=2 and probably also ford>2. Further, we show that multilevel range searching data structures can be built with only a polylogarithmic overhead in space and query time per level (the previous solutions require at least a small fixed power ofn). We show that Hopcroft's problem (detecting an incidence amongn lines andn points) can be solved in time % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9qqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOBamaaCa% aaleqabaGaaGinaiaac+cacaaIZaaaaOGaaGOmamaaCaaaleqabaGa% am4taiaacIcaciGGSbGaai4BaiaacEgadaahaaadbeqaaiaaisdaaa% WccaWGUbGaaiykaaaaaaa!40F5! $$n^{4/3} 2^{O(\log ^4 n)}$$ . In all these algorithms we apply Chazelle's results on computing optimal cuttings.

Anthropometric and anthroposcopic findings of the nasal and facial region in cleft patients before and after primary lip and palate repair.

Abstract: Two populations were studied and compared to determine the effects of cleft lip and palate surgery on the nose and face. In the first, three anthropometric measurements, two nasal and one facial, were taken before primary lip repair from infants with complete unilateral cleft lip and palate (UCLP) and with bilateral cleft lip and palate (BCLP). In the second, ten measurements were taken from the nose and face of patients surgically treated for UCLP and BCLP. The high frequency of noses disproportionately wide in relation to their height in both cleft types before primary lip repair greatly decreased after surgery. Among the residual deformities after surgery for UCLP, nostril floor width asymmetry was the most frequent, followed by columella length asymmetry, flat nasal bridge, wide soft nose, flat nasal tip, and small nasal tip protrusion. In the BCLP patients, nostril floor width asymmetry was also the most common stigma, followed by flat nasal tip, wide soft nose, columella length asymmetry, flat nasal bridge and bilaterally angled alae, and small nasal tip protrusion. A subnormally flat upper face inclination was observed in UCLP and BCLP patients. Quantitative determination of these nasal stigmata in cleft lip and palate patients who have undergone primary lip repair provides valuable information for surgical correction of the cleft soft-tissue deformities.

The SAPHO syndrome.

Abstract: We report two cases of the SAPHO syndrome (synovitis, acne conglobata, pustulosis palmoplantaris, hyperostosis and osteitis). This syndrome has been published in the pediatric and rheumatological literature in recent years.

Laplacian eigenvalues and the maximum cut problem

Abstract: We introduce and study an eigenvalue upper boundź(G) on the maximum cut mc (G) of a weighted graph. The functionź(G) has several interesting properties that resemble the behaviour of mc (G). The following results are presented. We show thatź is subadditive with respect to amalgam, and additive with respect to disjoint sum and 1-sum. We prove thatź(G) is never worse that 1.131 mc(G) for a planar, or more generally, a weakly bipartite graph with nonnegative edge weights. We give a dual characterization ofź(G), and show thatź(G) is computable in polynomial time with an arbitrary precision.

The Splotch mutation interferes with muscle development in the limbs

Abstract: Homozygosity for the Splotch mutation causes neural tube and neural crest defects in mice. It has been demonstrated that Splotch mutant mice carry mutations in the homeodomain of the Pax-3 gene. Pax-3 is expressed in the neural tube, some neural crest derivatives, the mesenchyme of the limb bud and the somites. We have examined the development of the somite-derived skeletal muscles in homozygotes carrying the Splotch (Sp1H) mutation. Our results suggest that the Splotch mutation affects the development of skeletal muscles in a region-specific way: 1. The expression of the CMZ transgene in homozygotes reveals a disorganisation of the dermomyotome in whole stained embryos. 2. The axial musculature is reduced in size along a rostro-caudal gradient. 3. The muscle anlagen in the limbs develop much more slowly. Muscles of the head and the ventral body wall are normally developed in the mutant on day 13.5 of gestation. Recently, it has been shown that the myogenic precursors of the limbs are derived from the lateral half of the somite. The specific disturbance of muscle development in the limbs of Splotch mutants thus suggests a role for Pax-3 in the organisation of the somite, the production of trophic factors in the limb mesenchyme or an alteration of myogenic and mesenchymal cells.

Tests of linear hypotheses based on regression rank scores

Abstract: We propose a general class of asymptotically distribution-free tests of a linear hypothesis in the linear regression model. The tests are based on regression rank scores, recently introduced by Gut...

The H 1 liquid argon calorimeter system

Abstract: The liquid argon calorimeter of the H 1 detector presently taking data at the HERA ep collider at DESY, Hamburg, is described. The main physics requirements and the most salient design features relevant to this calorimeter are given. The aim to have smooth and hermetic calorimetric coverage over the polar angular range 4° ≤ θ ≤ 154° is achieved by a single liquid argon cryostat containing calorimeter stacks structured in wheels and octants for easy handling. The absorber materials used are lead in the electromagnetic part and stainless steel in the hadronic part. The read-out system is pipelined to reduce the dead time induced by the high trigger rate expected at the HERA collider where consecutive bunches are separated in time by 96 ns. The main elements of the calorimeter, such as the cryostat, with its associated cryogenics, the stack modules, the read-out, calibration and trigger electronics as well as the data acquisition system are described. Performance results from data taken in calibration runs with full size H 1 calorimeter stacks at a CERN test beam, as well as results from data collected with the complete H 1 detector using cosmic rays during the initial phase of ep operations are presented. The observed energy resolutions and linearities are well in agreement with the requirements.

Eigenvalues in Combinatorial Optimization

Abstract: In the last decade many important applications of eigenvalues and eigenvectors of graphs in combinatorial optimization were discovered. The number and importance of these results is so fascinating that it makes sense to present this survey.

Results from pion calibration runs for the H 1 liquid argon calorimeter and comparisons with simulations

Abstract: We present results on calibration runs performed with pions at the CERN SPS for different modules of the H 1 liquid argon calorimeter which consists of an electromagnetic section with lead absorbers and a hadronic section with steel absorbers. The data cover an energy range from 3.7 to 205 GeV. Detailed comparisons of the data and simulation with GHEISHA 8 in the framework of GEANT 3.14 are presented. The measured pion induced shower profiles are well described by the simulation. The total signal of pions on an energy scale determined from electron measurements is reproduced to better than 3% in various module configurations. After application of weighting functions, determined from Monte Carlo data and needed to achieve compensation, the reconstructed measured energies agree with simulation to about 3%. The energies of hadronic showers are reconstructed with a resolution of about 50% √E ⨸ 2% . This result is achieved by inclusion of signals from an iron streamer tube tail catcher behind the liquid argon stacks.

Prosaposin deficiency: further characterization of the sphingolipid activator protein-deficient sibs. Multiple glycolipid elevations (including lactosylceramidosis), partial enzyme deficiencies and ultrastructure of the skin in this generalized sphingolipid storage disease.

Abstract: Sphingolipid activator protein (SAP) deficiency, previously described in two sibs and shown to be caused by the absence of the common saposin precursor (prosaposin), was further characterized by biochemical lipid and enzyme studies and by ultrastructural analysis. The 20 week old fetal sib had increased concentrations of neutral glycolipids, including mono-, di-, tri- and tetrahexosylceramide, in liver, kidney and cultured skin fibroblasts compared with the controls. Glucosylceramide and lactosylceramide were particularly elevated. The kidney of the affected fetus showed additional increases in the concentration of sulphatide, galactosylceramide and digalactosylceramide. Free ceramide was stored in the liver and kidney, and GM3 and GM2 gangliosides were elevated in the liver, but not the brain, of the fetus. Phospholipids, however, were normal in the affected fetus. In the liver biopsy of the propositus, who later died at 16 weeks of age, only a few lipids could be studied. Glucosylceramide, dihexosylceramide and ceramide were elevated in agreement with our previous study. Enzyme studies were undertaken using detergent free liposomal substrate preparations and fibroblast extracts. The sibs' β-glucocerebrosidase and β-galactocerebrosidase activities were clearly reduced, but their sphingomyelinase activities were normal. The normal activity of the latter enzyme and the almost normal tissue concentration of sphingomyelin in prosaposin deficiency suggest that the prosaposin derived SAPs are not required for sphingomyelinase activity in vivo. In keeping with the biochemical findings, skin biopsies from the sibs showed massive lysosomal storage with a vesicular and membranous ultrastructure. The function of SAPs in sphingolipid degradation and the role of SAPs for enzyme activity in vitro are discussed. In addition, the similarity in neutral glycolipid accumulations in Niemann Pick disease type C and in prosaposin deficiency are noted. The phenotype of the prosaposin deficient sibs resembled acute neuronopathic (type 2) Gaucher disease more than Farber disease in several aspects, but their genotype was unique.

Classification of Transmissivity Magnitude and Variation

Abstract: Until now no objective classification of transmissivity has been introduced, in spite of the quantitative nature of transmissivity values and their obvious importance for quantitative appraisals of aquifers or major ground-water systems. The usual subjective expression of transmissivity, for example as “high” or “low”, prevents the objective comparison of transmissivity values characterizing different areas and hydrogeological environments. A combined classification of magnitude and variation of transmissivity is proposed, with the intention to standardize the expression, comparison, and representation of transmissivity. This classification also enables its compact and unambiguous depiction in tables and maps.

On the non-newtonian incompressible fluids

Abstract: The Navier-Stokes equations can be included as a special case into the class of non-Newtonian incompressible fluids with the nonlinear stress tensor τ=τ(e), the components of which satisfy the p-growth condition. Measure-valued solutions already exist for p>2n/(n+2). For the space periodic problem, the existence of the weak solution is then obtained for p>3n/(n+2). These solutions are regular and unique for p≥1+2n/(n+2).

Discrepancy and approximations for bounded VC-dimension

Abstract: Let (X, ℛ) be a set system on ann-point setX. For a two-coloring onX, itsdiscrepancy is defined as the maximum number by which the occurrences of the two colors differ in any set in ℛ. We show that if for anym-point subset $$Y \subseteq X$$ the number of distinct subsets induced by ℛ onY is bounded byO(m d) for a fixed integerd, then there is a coloring with discrepancy bounded byO(n 1/2−1/2d(logn)1+1/2d ). Also if any subcollection ofm sets of ℛ partitions the points into at mostO(m d) classes, then there is a coloring with discrepancy at mostO(n 1/2−1/2dlogn). These bounds imply improved upper bounds on the size of e-approximations for (X, ℛ). All the bounds are tight up to polylogarithmic factors in the worst case. Our results allow to generalize several results of Beck bounding the discrepancy in certain geometric settings to the case when the discrepancy is taken relative to an arbitrary measure.

Testing four elastic finite-difference schemes for behavior at discontinuities

Abstract: Three second-order and one fourth-order finite-difference schemes are theoretically and numerically investigated for their behavior at elastic discontinuities. One of them is extended with new formulas for a flat free surface. Two of the schemes are consistent with the stress-continuity condition for P-SV waves at discontinuities coinciding with horizontal (or vertical) grid lines; none of them is consistent at diagonal discontinuities. Despite these significant theoretical differences, the numerical results from all four schemes are very similar. Moreover, the results compare well with semianalytic solutions for three different models. A practical conclusion is that the recent finite-difference schemes are by no means free from the accuracy problems at elastic discontinuities. Nevertheless, the schemes provide synthetic seismograms whose differences are well below the level normally introduced by structural and focal uncertainties.

One more occurrence of variables makes satisfiability jump from trivial to NP-complete

Abstract: A Boolean formula in a conjunctive normal form is called a $(k,s)$ – formula if every clause contains exactly k variables and every variable occurs in at most s clauses. The $(k,s)$–${\text{SAT}}$ problem is the SATISFIABILITY problem restricted to $(k,s)$–formulas. It is proved that for every $k \geqslant 3$ there is an integer $f(k)$ such that $(k,s)$–${\text{SAT}}$ is trivial for $s \leqslant f(k)$ (because every $(k,s)$–formula is satisfiable) and is NP-complete for $s \geqslant f(k) + 1$. Moreover, $f(k)$ grows exponentially with k, namely, $\lfloor {{{2^k } / {ek}}} \rfloor \leqslant f(k) \leqslant 2^{k - 1} - 2^{k - 4} - 1$ for $k \geqslant 4$.

Relativistic disks as sources of the Kerr metric.

Abstract: Many spacetimes are known which should represent gravitational fields outside rotating sources, but for which no satisfactory sources have been found. We indicate that these spacetimes can arise as the metrics of counterrotating thin disks of finite mass, consisting of two streams of collisionless particles, circulating in opposite directions with different velocities. We show how such disks can act as exact sources of all types of the Kerr metric. In their central regions they can produce ergoregions, the velocities can approach that of light, and the redshifts can becomes arbitrarily large.

The Effect of Chronic Nicotine Administration on Bone Mineral Content in Mice.

Abstract: Tobacco use has been identified as being a risk factor for the development of osteoporosis. To elucidate the effect of nicotine on bone metabolism we examined 8 intact and 8 castrated mice treated for 56 days with nicotine in drinking water and compared with the same number of mice acting as controls. The mineral bone mass in the femora of the animals was measured quantitatively. A significant reduction of bone density and bone mineral content was found in the nicotine treated animals compared to animals without nicotine. Nicotine itself does not exert any antiandrogenic effect, and it does not produce changes in the weight of seminal vesicles.

Portevin-Le chatelier instabilities in Al-3 Mg conditioned by strain rate and strain

Abstract: The critical strains for the occurrence of the Portevin-Le Châtelier effect have been measured as a function of the strain rate for Al-3 Mg alloy polycrystals deformed at room temperature. Experimental results are compared with the model proposed by Kubin and Estrin. It is shown that the explanation of the occurrence of the onset termination of jerky flow at low strain rates needs new information to modify the evolution law for the densities of forest and mobile dislocations used by Kubin and Estrin.

In Vitro Induced Anaerobic Resistance to Metronidazole In Trichomonas Vaginalis

Abstract: Resistance to metronidazole detectable under anaerobic conditions was induced in two Trichomonas vaginalis strains (TV 10-02 and MRP-2) by cultivation at gradually increasing pressure of the drug (1-100 micrograms/ml) for 12 to 21 months. The resistant derivatives reproduced in anaerobic trypticase-yeast-extract-maltose medium at 100 micrograms/ml metronidazole and showed very high values of minimal lethal concentration for metronidazole in anaerobic in vitro assays (556-1,600 micrograms/ml at 48-h exposure to the drug). Stepwise selection was necessary to develop the resistance in either strain. Attempts to induce resistance by prolonged maintenance of trichomonads with constant, low or moderate drug concentrations (3-10 micrograms/ml) were unsuccessful. Freshly developed resistance to high concentrations of metronidazole was unstable in absence of drug pressure as well as after cryopreservation. Development of stable resistance required further cultivation at 100 micrograms/ml metronidazole. Unstable substrains did not revert to original susceptibility. They retained a moderate level of resistance, being able to grow at 10 micrograms/ml metronidazole. The strains with fully developed resistance had no activity of the hydrogenosomal enzymes pyruvate: ferredoxin oxidoreductase and hydrogenase and ceased uptake of [14C]-metronidazole. These findings indicate that the pyruvate oxidizing pathway responsible for metronidazole activation was inactivated and metabolism of the drug stopped.

Microstructures and hardness of ultrafine-grained Ni3Al

Abstract: The microstructural evolution of the ultrafine-grained intermetallic compound Ni 3 Al is studied as a function of annealing at different temperatures. The ultrafine microstructure is produced by a high plastic torsional straining. Transmission electron microscopy, X-ray diffraction and differential scanning calorimetry are used to characterize the microstructural evolution and microhardness is used to determine mechanical behaviour. The as-deformed microstructure exhibits an almost fully disordered crystalline structure with coherent domain size of about 18 nm, a strong torsional texture and high internal elastic strains. On annealing the as-deformed samples at different temperatures, the recrystallization of the material into a granular type structure containing non-equilibrium grain boundaries is first observed. This is followed by the transformation from non-equilibrium grain boundaries with simultaneous grain growth. This transformation is correlated with an increase of hardness. A new concept of non-equilibrium grain boundaries transparency is presented to interpret this singular behaviour. The results are compared to those obtained on an ultrafine-grained Al-1.5% Mg alloy produced by the same technique and which exhibits the same mechanical behaviour.

Abdominal body mass distribution and elevated blood pressure are associated with increased risk of death from cardiovascular diseases and cancer in middle-aged men. The results of a 15- to 20-year follow-up in the Paris prospective study I.

Abstract: The associations of blood pressure (BP), body mass index (BMI) and iliac-to-thigh circumference index (CI) with total, cardiovascular and cancer mortality were investigated in 7312 middle-aged men, initially free of coronary heart disease, known cancer and not treated for hypertension, who have been followed for 15 to 20 years in the Paris prospective study I. Using Cox survival regression analysis, total mortality (1208 deaths) was found to be highest in relatively lean men (BMI or = 96 mmHg) and central pattern of body mass distribution (CI > 1.82). Cancer causes accounted for a large proportion of the increased mortality risk. In parallel, mortality from cardiovascular diseases increased independently with blood pressure and iliac-to-thigh circumference index, but increased with body mass index only in men with low blood pressure (mean BP < 96 mmHg). Taking into account serum cholesterol and cigarette smoking levels as covariates and excluding deaths occurring 5 to 10 years after the examination only slightly attenuated the intensity of this pattern of association.

Droplet dynamics for asymmetric Ising model

Abstract: Nucleation from a metastable state is studied for an anisotropic Ising model at very low temperatures. It turns out that the critical nucleus as well as configurations on a typical path to it differ from the Wulff shape of an equilibrium droplet.