Gossypol (Gp), the natural product of a polyphenolic nature, is known to form a large variety of inclusion compounds with solvent molecules as the guest components.From aprotic solvents Gp inclusion compounds are formed that are based on the host matrix constructued from columnar Gp assemblies, that in the highest symmetrical case belong to the P12/c1 rod group [1].This group of compounds is represented by unstable Gp/CHCl 3 (1/1) inclusion compound that crystallizes in the C2/c space group with Z'=1.It has been proposed that desolvation of this compound proceeds stepwise via crystalline forms with the 4:3, 4:2 and 4:1 host:guest ratio [2].Indeed, inclusion compounds having these stoichiometries and constructed from similar host columnar aggregates were prepared when Gp was recrystallized from toluene, benzene and p-xylene, respectively.Moreover, the intermediate form of Gp/CHCl 3 inclusion compound with the 4:2 host: guest ratio was also obtained.To our surprise, when Gp was recrystallized from a mixture of solvents: CHCl 3 /benzene, CHCl 3 /toluene, CHCl 3 /p-xylene, stable ternary inclusion compounds were formed with the aromatic molecules (Ar) occupying every second centrosymmetric void in the basic Gp/CHCl 3 (1/1) matrix.These inclusion compounds have Gp/CHCl 3 /Ar ratio of 4/4/1 and crystallize in the P-1 or P2 1 /c space groups with Z'=4.Similar ternary compounds were also obtained with naphthalene or pentafluoroaniline as the third component.In turn, when Gp crystallization was performed from mixtures of CHCl 3 with o-or m-xylenes another group of ternary inclusion compounds was obtained with Gp/CHCl 3 /Ar ratio of 4/2/1 (P2 1 /c, Z' = 2).Structure of these compounds is to a large extent isostructural with the binary inclusion compound Gp/toluene (4/3), but with two symmetry independent guest sites occupied in ternary compounds by different guest components.In addition to structural studies, stability data for the ternary Gp compounds will be presented.
Semiconductor nanowires (NW) possess several beneficial properties for efficient conversion of solar energy into electricity and chemical energy. Due to their efficient absorption of light, short distances for minority carriers to travel, high surface-to-volume ratios, and the availability of scalable synthesis methods, they provide a pathway to address the low cost-to-power requirements for wide-scale adaptation of solar energy conversion technologies. Here we highlight recent progress in our group towards implementation of NW components as photovoltaic and photoelectrochemical energy conversion devices. An emphasis is placed on the unique properties of these one-dimensional (1D) structures, which enable the use of abundant, low-cost materials and improved energy conversion efficiency compared to bulk devices.
Impulsive control of a chaotic system is ideal for designing digital control schemes where the control laws are generated by digital devices which are discrete in time. In this paper, several theorems on the stability of impulsive control systems are presented. These theorems are then used to find the conditions under which the chaotic systems can be asymptotically controlled to the origin by using impulsive control. Given the parameters of the chaotic system and the impulsive control law, an estimation of the upper bound of the impulse interval is given. We also present a theory of impulsive synchronization of two chaotic systems. A promising application of impulsive synchronization of chaotic systems to a secure communication scheme is presented. In this secure communication scheme, the transmitted signals are divided into small time frames. In each time frame, the synchronization impulses and the scrambled message signal are embedded. Conventional cryptographic methods are used to scramble the message signal. Simulation results based on a typical chaotic system; namely, Chua's oscillator, are provided.
Distributed Algorithmic Mechanism Design (DAMD) combines theoretical computer science's traditional focus on computational tractability with its more recent interest in incentive compatibility and distributed computing. The Internet's decentralized nature, in which distributed computation and autonomous agents prevail, makes DAMD a very natural approach for many Internet problems. This paper first outlines the basics of DAMD and then reviews previous DAMD results on multicast cost sharing and interdomain routing. The remainder of the paper describes several promising research directions and poses some specific open problems..
Abstract Natural killer (NK) cell receptors regulate the capacity of NK cells and in some cases T cells to attack tumor cells and infected cells. Cancer cells become susceptible to NK cells by up-regulating stimulatory ligands, such as the Raet1/Mult1/H60/ULBP/MICA families of proteins recognized by the NKG2D receptor. This presentation will discuss the role of activating receptors such as NKG2D in tumor surveillance in vivo and the molecular mechanisms and signaling pathways responsible for induction of NKG2D ligands in cancer cells and their relationship to major pathways regulating tumorigenesis. Evidence will be presented that tumor associated stress pathways induce NKG2D ligands by acting at distinct levels of biogenesis (transcription, mRNA stabilization, protein stabilization). The role of NKG2D recognition in mobilizing lymphocytes against tumors in vivo will be discussed. Supported by grants from NCI, NIAID and Prostate Cancer Foundation. Citation Information: Cancer Prev Res 2011;4(10 Suppl):CN08-03.
We propose a new approach for vision based longitudinal and lateral vehicle control which makes extensive use of binocular stereopsis. Longitudinal control --- i.e. maintaining a safe, constant distance from the vehicle in front --- is supported by detecting and measuring the distances to leading vehicles using binocular stereo. A known camera geometry with respect to the locally planar road is used to map the images of the road plane in the two camera views into alignment. Any significant residual image disparity then indicates an object not lying in the road plane and hence a potential obstacle. This approach allows us to separate image features into those lying in the road plane, e.g. lane markers, and those due to other objects. The features which lie on the road are stationary in the scene and appear to move only because of the egomotion of the vehicle. Measurements on these features are used for dynamic update of (a) the camera parameters in the presence of camera vi...
Enynes are easily accessible building blocks as a result of the rich chemistry of alkynes and thus represent attractive substrates for ring formation. A ruthenium catalyst for cycloisomerization effects such reaction of 1,6- and 1,7-enynes typically at room temperature in acetone or DMF under neutral conditions. The reaction is effective for forming five- and six-membered rings of widely divergent structure. The alkyne may bear both election-donating and election-withdrawing substituents. The alkene may be di- or trisubstituted. Introduction of a quaternary center at the propargylic position of an ynoate, however, completely changes the nature of the reaction. In the case of a 1,6-enynoate, a seven-membered ring forms in excellent yield under equally mild conditions. Evidence is presented to indicate a complete change in mechanism. In the former case, the reaction involves the intermediacy of a ruthenacyclopentene. In the latter case, a C-H insertion to form a pi-allylruthenium intermediate is proposed and supported by deuterium-labeling studies. A rationale is presented for the structural dependence of the mechanism.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
At a deciduous forest in the southeast United States (Walker Branch Watershed, Oak Ridge, Tennessee), as at other sites with tall vegetation and/or complex terrain, it is difficult to temporally integrate eddy covariance data to obtain long‐term estimates of net ecosystem exchange of carbon dioxide (NEE), primarily because of suspected systematic nocturnal errors. Therefore, although eddy covariance data can be invaluable, additional tools such as empirical gap‐filling methods, independent measurements of CO 2 flux using chambers, and simulations using canopy process models are often necessary to obtain reliable annual carbon uptake estimates. Two independent approaches for estimating annual NEE using these tools at the Walker Branch site are discussed. One approach is to cumulatively sum the full set of eddy covariance measurements over time. The second approach is to sum the output of NEE from a biophysical canopy exchange model (CANOAK). CANOAK incorporates independent chamber measurements on leaves, soil, and stems and is driven using the observed canopy architecture, meteorology, soil water content, and soil temperatures to predict NEE. Both methods estimate similar trends and magnitudes of daytime (daylight hours) soil respiration and NEE over 5 years. Both methods also suggest similar differences among years (interannual variability). These two estimates of NEE are used to address possible measurement bias errors at this site and to provide plausible estimates of annual NEE. The estimated mean annual NEE at this site is −574 g C m −2 yr −1 between 1995 and 1999, ranging from −470 g C m −2 y −1 (1995) to −629 g C m −2 yr −1 (1999) (negative NEE indicates uptake by forest).
Congestion is a longstanding problem in datagram networks. One congestion avoidance technique is feedback flow control, in which sources adjust their transmission rate in response to congestion signals sent (implicitly or explicitly) by network gateways. The goal is to design flow control algorithms which provide time-scale invariant, fair, stable, and robust performance. In this paper we introduce a simple model of feedback flow control, in which sources make synchronous rate adjustments based on the congestion signals and other local information, and apply it to a network of Poisson sources and exponential servers. We investigate two different styles of feedback, aggregate and individual, and two different gateway service disciplines, FIFO and Fair Share. The purpose of this paper is to identify, in the context of our simple model, which flow control design choices allow us to achieve our performance goals.
To analyze the synthesis, structure and function of the plant cell wall by a genetic approach, 5200 chemically mutagenized Arabidopsis plants were screened for changes in the monosaccharide composition of hydrolyzed cell wall material by gas chromatography of alditol acetates. This screening procedure identified 23 mutant lines representing 11 different loci designated mur1 to mur11 . The mur lines fall into essentially three groups: (1) complete absence of a monosaccharide, (2) significant reduction in the amount of a single monosaccharide, and (3) complex alterations in the relative amounts of several monosaccharides. All mutants in the first category represent alleles of the mur1 locus, and are deficient in the de novo synthesis of fucose. Mutants with reductions in a single monosaccharide have been identified for fucose ( mur2, mur3 ), arabinose ( mur4, mur5, mur6, mur7 ), and rhamnose ( mur8 ). Mutants with complex changes in monosaccharide composition are represented by the mur9 , mur10 and mur11 loci. Most of the mutant lines did not show obvious morphological or physiological alterations; however, lines mur1, mur9 and mur10 co‐segregated with reduced vigor or dwarfism of the plants. These results demonstrate the feasibility of identifying plants with altered cell wall compositions via a biochemical screening procedure. The availability of these mutants provides novel opportunities to study the functions of cell wall polysaccharides, gain insight into the biosynthesis of cell wall material, and clone cell wall‐related genes.
Abstract Chlormethyliertes, vernetztes Polystyrol (I) liefert mit Malodinitril in Gegenwart von Alkali das Dinitril (II), aus dem durch Reduktion mit Lithiumalanat das Diamin (III) entsteht.
