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Search Results: 1 - 10 of 325486 matches for " S. Baum "
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Transcript accumulation of putative drought responsive genes in drought-stressed chickpea seedlings
M Medini, M Baum, S Hamza
African Journal of Biotechnology , 2009,
Abstract: No
Information-theoretic analysis of MIMO channel sounding
Daniel S. Baum,Helmut B?lcskei
Mathematics , 2007,
Abstract: The large majority of commercially available multiple-input multiple-output (MIMO) radio channel measurement devices (sounders) is based on time-division multiplexed switching (TDMS) of a single transmit/receive radio-frequency chain into the elements of a transmit/receive antenna array. While being cost-effective, such a solution can cause significant measurement errors due to phase noise and frequency offset in the local oscillators. In this paper, we systematically analyze the resulting errors and show that, in practice, overestimation of channel capacity by several hundred percent can occur. Overestimation is caused by phase noise (and to a lesser extent frequency offset) leading to an increase of the MIMO channel rank. Our analysis furthermore reveals that the impact of phase errors is, in general, most pronounced if the physical channel has low rank (typical for line-of-sight or poor scattering scenarios). The extreme case of a rank-1 physical channel is analyzed in detail. Finally, we present measurement results obtained from a commercially employed TDMS-based MIMO channel sounder. In the light of the findings of this paper, the results obtained through MIMO channel measurement campaigns using TDMS-based channel sounders should be interpreted with great care.
A Simple Model to Explain Expensive Index Call Options  [PDF]
Sang Baum Kang
Theoretical Economics Letters (TEL) , 2017, DOI: 10.4236/tel.2017.73024
Abstract: According to the empirical finance literature, S&P 500 Index call options frequently violate the stochastic dominance upper bounds. In other words, index call options in the US are frequently overpriced. I propose a theoretical model to explain the reason for this. A simple economic model in this article reveals that when agents are sufficiently heterogeneous, a call option may be overpriced from the perspective of the representative agent. The key economic intuitions can be summarized as follows: First, if agents are sufficiently heterogeneous, a bullish agent, who is hungry for the “exposure” to a stock, may buy an expensive call option from a constrained bearish agent. Second, even though a call option is fairly priced from the perspectives of heterogeneous market participants, it may be overpriced from the perspective of the representative agent. Assuming reasonable parameters of heterogeneity, I find that a call option price violates the representative agent’s stochastic dominance upper bound.
The Stochastic Dominance Violation of Index Call Options in the Presence of Market Makers  [PDF]
Sang Baum Kang
Theoretical Economics Letters (TEL) , 2018, DOI: 10.4236/tel.2018.89103
Abstract: Finance researchers have been debating over whether index options are overpriced. Most debates have focused on expensive out-of-the-money put options. However, the stochastic dominance literature has argued that S & P 500 Index call options are frequently overpriced in the sense that every rational agent can improve her expected utility by writing these call options that violate the stochastic dominance upper bound. Hence, expensive index call options are also an unsolved puzzle in the finance literature. On the other hand, recent finance papers find that market makers play an important role in the pricing of index options. In this paper, I explore how constrained market makers interact with heterogeneity in beliefs and index option prices. Specifically, I develop an equilibrium model that accommodates previous empirical/theoretical results related to heterogeneity in beliefs, limits or arbitrage, and the role of market makers. The incremental findings from my model can be summarized as follows. First, even with the presence of market makers, the stochastic dominance upper bound violation of index call options occurs when heterogeneity in beliefs is sufficiently large. This result is novel, insomuch as someone may argue that if heterogeneous end-users share the risk themselves, heterogeneity in the presence of constrained market makers may not lead to option mispricing. Second, as the market maker is more constrained, the stochastic dominance upper bound violation becomes more severe. This paper is related to and contributes to the growing literature on the puzzle of index options. In addition, this paper complements the literature on the role of market makers in index option markets and the stochastic dominance literature.
Characterization of the hemagglutinin receptor specificity and neuraminidase substrate specificity of clinical isolates of human influenza A viruses
Couceiro, J. N. S. S.;Baum, L. G.;
Memórias do Instituto Oswaldo Cruz , 1994, DOI: 10.1590/S0074-02761994000400015
Abstract: six clinical isolates of influenza a viruses were examined for hemagglutinin receptor specificity and neuraminidase substrate specificity. all of the viral isolates minimally passaged in mammalian cells demonstrated preferential agglutination of human erythrocytes enzymatically modified to contain neuac α 2,6gal sequences, with no agglutination of cells bearing neuac α 2,3gal sequences. this finding is consistent with the hemagglutination receptor specificity previously demonstrated for laboratory strains of influenza a viruses. the neuraminidase substrate specificities of the clinical isolates examined were also identical to that described for the n2 neuraminidase of recent laboratory strains of human influenza viruses. the h3n2 viruses all displayed the ability to release sialic acid from both α 2, 3 and α 2, 6 linkages. in addition, two clinical isolates of h1n1 viruses also demonstrated this dual neuraminidase substrate specificity, a characteristic which has not been previously described for the n1 neuraminidase. these results demonstrate that complementary hemagglutinin and neuraminidase specificities are found in recent isolates of both h1n1 and h3n2 influenza viruses.
Secrets in secretions: genes that control nematode parasitism of plants
Hussey, Richard S.;Davis, Eric L.;Baum, Thomas J.;
Brazilian Journal of Plant Physiology , 2002, DOI: 10.1590/S1677-04202002000300002
Abstract: the most evolutionary advanced adaptations for plant parasitism by nematodes are the products of parasitism genes expressed in their esophageal gland cells and secreted through their stylet into host tissue to control the complex process of parasitism. molecular analyses of nematode parasitism genes are revealing the complexity of the tools a nematode possesses that enable it to attack plants and paints a more elaborate picture of host cellular events under specific control by the parasite than previously hypothesized. interestingly, the majority of the nematode parasitism genes discovered encodes proteins unique to plant parasites. identifying the complete profile of parasitism genes expressed throughout the parasitic cycle of a nematode is the key to understanding the molecular basis of nematode parasitism of plants and identifying vulnerable points in the parasitic process that can be interfered with to achieve nematode control to limit nematode-induced yield losses in crops.
Comparison of cloud statistics from spaceborne lidar systems
S. Berthier, P. Chazette, J. Pelon,B. Baum
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2008,
Abstract: The distribution of clouds in a vertical column is assessed on the global scale through analysis of lidar measurements obtained from three spaceborne lidar systems: LITE (Lidar In-space Technology Experiment, NASA), GLAS (Geoscience Laser Altimeter System, NASA), and CALIOP (Cloud-Aerosol LIdar with Orthogonal Polarization). Cloud top height (CTH) is obtained from the LITE profiles based on a simple algorithm that accounts for multilayer cloud structures. The resulting CTH results are compared to those obtained by the operational algorithms of the GLAS and CALIOP instruments. Based on our method, spaceborne lidar data are analyzed to establish statistics on the cloud top height. The resulting columnar results are used to investigate the inter-annual variability in the lidar cloud top heights. Statistical analyses are performed for a range of CTH (high, middle, low) and latitudes (polar, middle latitude and tropical). Probability density functions of CTH are developed. Comparisons of CTH developed from LITE, for 2 weeks of data in 1994, with ISCCP (International Satellite Cloud Climatology Project) cloud products show that the cloud fraction observed from spaceborne lidar is much higher than that from ISCCP. Another key result is that ISCCP products tend to underestimate the CTH of optically thin cirrus clouds. Significant differences are observed between LITE-derived cirrus CTH and both GLAS and CALIOP-derived cirrus CTH. Such a difference is due primarily to the lidar signal-to-noise ratio that is approximately a factor of 3 larger for the LITE system than for the other lidars. A statistical analysis for a full year of data highlights the influence of both the Inter-Tropical Convergence Zone and polar stratospheric clouds.
Improving predictive power of physically based rainfall-induced shallow landslide models: a probabilistic approach
S. Raia,M. Alvioli,M. Rossi,R. L. Baum
Geoscientific Model Development Discussions , 2013, DOI: 10.5194/gmdd-6-1367-2013
Abstract: Distributed models to forecast the spatial and temporal occurrence of rainfall-induced shallow landslides are deterministic. These models extend spatially the static stability models adopted in geotechnical engineering and adopt an infinite-slope geometry to balance the resisting and the driving forces acting on the sliding mass. An infiltration model is used to determine how rainfall changes pore-water conditions, modulating the local stability/instability conditions. A problem with the existing models is the difficulty in obtaining accurate values for the several variables that describe the material properties of the slopes. The problem is particularly severe when the models are applied over large areas, for which sufficient information on the geotechnical and hydrological conditions of the slopes is not generally available. To help solve the problem, we propose a probabilistic Monte Carlo approach to the distributed modeling of shallow rainfall-induced landslides. For the purpose, we have modified the Transient Rainfall Infiltration and Grid-Based Regional Slope-Stability Analysis (TRIGRS) code. The new code (TRIGRS-P) adopts a stochastic approach to compute, on a cell-by-cell basis, transient pore-pressure changes and related changes in the factor of safety due to rainfall infiltration. Infiltration is modeled using analytical solutions of partial differential equations describing one-dimensional vertical flow in isotropic, homogeneous materials. Both saturated and unsaturated soil conditions can be considered. TRIGRS-P copes with the natural variability inherent to the mechanical and hydrological properties of the slope materials by allowing values of the TRIGRS model input parameters to be sampled randomly from a given probability distribution. The range of variation and the mean value of the parameters can be determined by the usual methods used for preparing the TRIGRS input parameters. The outputs of several model runs obtained varying the input parameters are analyzed statistically, and compared to the original (deterministic) model output. The comparison suggests an improvement of the predictive power of the model of about 10% and 16% in two small test areas, i.e. the Frontignano (Italy) and the Mukilteo (USA) areas, respectively. We discuss the computational requirements of TRIGRS-P to determine the potential use of the numerical model to forecast the spatial and temporal occurrence of rainfall-induced shallow landslides in very large areas, extending for several hundreds or thousands of square kilometers. Parallel execution of the code usin
E-Learning in der allgemeinmedizinischen Weiterbildung
S?nnichsen, Andreas C.,Donner-Banzhoff, N.,Baum, E.
GMS Zeitschrift für Medizinische Ausbildung , 2005,
Short-lived pollutants in the Arctic: their climate impact and possible mitigation strategies
P. K. Quinn,T. S. Bates,E. Baum,N. Doubleday
Atmospheric Chemistry and Physics Discussions , 2007,
Abstract: Several short-lived pollutants known to impact Arctic climate may be contributing to the accelerated rates of warming observed in this region relative to the global annually averaged temperature increase. Here, we present a summary of the short-lived pollutants that impact Arctic climate including methane, tropospheric ozone, and tropospheric aerosols. For each pollutant, we provide a description of the major sources, the mechanism of forcing, seasonally averaged forcing values for the Arctic, and the corresponding surface temperature response. We suggest strategies for reducing the warming based on current knowledge and discuss directions for future research to address remaining uncertainties.
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