Total risk aversion,stochastic optimal control,and differential games

We present a connection between the theory of risk in the context of a stochastic optimal control problem and its relation to the theory of differential games. In particular, we define the notion of total risk aversion from the viewpoint of the upper value of a differential game. We prove that as the index of absolute risk aversion of a utility function in a stochastic control problem converges to infinity the (certainty equivalent) optimal payoff converges to the upper value of an associated deterministic differential game. The two main points of this paper are (1) a precise characterization oftotal risk aversion and (2) the construction of a stochastic optimal control problem intimately connected to a deterministic differential game.Partially supported by the Air Force Office of Scientific Research Grant No. AFOSR-86-0202.Partially supported by a grant from the National Science Foundation.     

Determination of absolute configurations from vibrational raman optical activity: (trans)-2,3-dimethylthiirane

Experimental and theoretical vibrational Raman optical activity (VROA) spectra of (2R,3R)-2,3-dimethylthiirane in the 200-1500 cm(-1) region are presented. The level of agreement obtained for the observed and predicted VROA signs suggests that the absolute configurations of chiral molecules can be determined confidently using VROA.     

Transition-metal complexes of a bifunctional tetradentate gallium alkoxide ligand

The mixed gallium transition-metal complexes [FeCl[Ga(2)((t)Bu)(4)(neol)(2)]] (1) and [M[Ga(2)((t)Bu)(4)(neol)(2)]], M = Co (2), Ni (3), Cu (4), have been prepared by the reaction of [Ga(2)((t)Bu)(4)(neol-H)(2)] (neol-H(2) = 2,2-dimethyl-propane-1,3-diol) with the appropriate metal halide and Proton Sponge. Compounds 1-4 have been characterized by NMR (3), UV/vis, and IR spectroscopy and magnetic susceptibility (solution and solid state), and their molecular structures have been confirmed by X-ray crystallography. The molecular structure of compounds 1-4 consists of a tetracyclic core formed from two four-membered and two six-membered rings. The central metal atom adopts a square pyramidal (1) or square planar (2-4) geometry. The magnetic susceptibilities for 1, 2, and 4 are as expected for strong ligand field environments. On the basis of spectroscopic and structural data, the [Ga(2)((t)Bu)(4)(neol)(2)](2-) ligand appears to be more flexible than other chelating ligands; this is proposed to be due to the flexibility in the O-Ga-O bond angle.     

Technical challenges in applying capillary electrophoresis-single strand conformation polymorphism for routine genetic analysis

Recent and future advances in population genetics will have a significant impact on health care practices and the economics of health care provision only if a spectrum of patient-tailored, effective methods of DNA screening for sequence alterations has been developed. Genetic screening by capillary electrophoresis-single strand conformation polymorphism (CE-SSCP), which is based upon the differences in electrophoretic mobilities of wild-type and mutant DNA species, offers an important complement to other presently available techniques such as Sanger sequencing and DNA hybridization arrays due to its simplicity, versatility, and low cost of analysis. A two-part review of CE-SSCP that discusses its advantages and limitations is presented. Emphasis is placed on technological aspects of CE-SSCP (including such rarely addressed issues as sample preparation protocols and the nature of the polymeric DNA separation matrix) as well as on the potential of CE-SSCP for routine genetic analysis. An attempt is made to organize and present the information in sufficient detail to allow the use of SSCP for routine genetic screening even by those inexperienced in CE. Some discussion of CE-based heteroduplex analysis (HA) is also presented.     

Glacial influences on solar radiation in a subarctic sea

Understanding macroscale processes controlling solar radiation in marine systems will be important in interpreting the potential effects of global change from increasing ultraviolet radiation (UV) and glacial retreat. This study provides the first quantitative assessment of UV in the water column of Prince William Sound, a subarctic, semienclosed sea surrounded by mountains, glaciers, rivers, bays and fjords in south central Alaska. Glacial influences on diffuse attenuation coefficients (Kd) were determined along an approximate 120 km transect running NE (61 degrees 07'43'N, 146 degrees 17'1'W) to SW (60 degrees 27'25'N, 148 degrees 05'27' W). Glacial meltwater and flour caused a 10-fold increase in Kd for visible light, UV-A and UV-B, whereas high optical clarity was present in a diversity of areas away from glacial influences. Transition areas and locations affected by calving of a tidewater glacier had intermediate Kd values. Depths at 99% attenuation ranged from less than 0.2 m near glacial streams to greater than 5 m in bays and open ocean distant from sources of glacial sediments. These results suggest that potential global change from increasing UV and glacial retreat may have heterogeneous effects on subarctic marine systems.     

Prediction of pesticide acute toxicity using two-dimensional chemical descriptors and target species classification

Previous modelling of the median lethal dose (oral rat LD₅₀) has indicated that local class-based models yield better correlations than global models. We evaluated the hypothesis that dividing the dataset by pesticidal mechanisms would improve prediction accuracy. A linear discriminant analysis (LDA) based-approach was utilized to assign indicators such as the pesticide target species, mode of action, or target species - mode of action combination. LDA models were able to predict these indicators with about 87% accuracy. Toxicity is predicted utilizing the QSAR model fit to chemicals with that indicator. Toxicity was also predicted using a global hierarchical clustering (HC) approach which divides data set into clusters based on molecular similarity. At a comparable prediction coverage (~94%), the global HC method yielded slightly higher prediction accuracy (r² = 0.50) than the LDA method (r² ~ 0.47). A single model fit to the entire training set yielded the poorest results (r² = 0.38), indicating that there is an advantage to clustering the dataset to predict acute toxicity. Finally, this study shows that whilst dividing the training set into subsets (i.e. clusters) improves prediction accuracy, it may not matter which method (expert based or purely machine learning) is used to divide the dataset into subsets.     

In vitro characterization of an electroactive carbon-nanotube-based nanofiber scaffold for tissue engineering

In an effort to reduce organ replacement and enhance tissue repair, there has been a tremendous effort to create biomechanically optimized scaffolds for tissue engineering applications. In contrast, the development and characterization of electroactive scaffolds has attracted little attention. Consequently, the creation and characterization of a carbon nanotube based poly(lactic acid) nanofiber scaffold is described herein. After 28 d in physiological solution at 37 °C, a change in the mass, chemical properties and polymer morphology is seen, while the mechanical properties and physical integrity are unaltered. No adverse cytotoxic affects are seen when mesenchymal stem cells are cultured in the presence of the scaffold. Taken together, these data auger well for electroactive tissue engineering.

     

Cross Coupling of Substituted Anilines with Quinoline: Synthesis and Structural Characterization of HN(py)quin,PhN(py)quin,MesN(py)quin,and [PhN(py)(H-quin)]BF<Subscript>4</Subscript>

Abstract  

The molecular structure of (2,6-ⁱPr₂C₆H₃)N(quin)₂ (1) and both the methanol and toluene solvates of its copper complex [Cu{(2,6-ⁱPr₂C₆H₃)N(quin)₂}₂]BF₄, 2·MeOH and 2.2(C₆H₅Me), respectively, have been determined. The quinolyl rings in 1 adopt anti-syn (C_Ar–N–C–N_quin) conformation as a result of π–π stacking. The cation in 2·MeOH crystallizes on a C₂ axis, while the cation in 2·2(C₆H₅Me) is crystallographically independent. As a result of intramolecular π–π stacking there are significant changes within the coordination geometry about the copper centers between the two solvates, suggesting that the coordination around copper is supple. Crystal data: 1 group P2₁/c, a = 8.614(1), b = 16.137(3), c = 17.601(4) ?, β = 93.32(3)°, V = 2,442.5(9) ?³, Z = 4, R = 0.0544, wR ₂ = 0.1340. 2·MeOH group P3₂21, a = 13.254(1), b = 13.254(1), c = 27.214(5) ?, V = 4,140(1) ?³, Z = 3, R = 0.0392, wR ₂ = 0.0917. 2.2(C₆H₅Me) group P1, a = 11.677(2), b = 16.261(3), c = 17.077(3) ?, α = 93.63(3), β = 97.30(3), γ = 96.26(3)°, V = 3,187(1) ?³, Z = 4, R = 0.0526, wR ₂ = 0.1221.     

Preparation,characterisation and modification of carbon‐based monolithic rods for chromatographic applications

A range of porous carbon‐based monolithic (PCM) rods with flow‐through pore sizes of 1, 2, 5 and 10 μm, were produced using a silica particle template method. The rods were characterised using SEM and energy‐dispersive X‐ray spectroscopy, BET surface area and porous structure analysis, dilatometry and thermal gravimetry. SEM evaluation of the carbon monolithic structures revealed an interconnected rigid bimodal porous structure and energy‐dispersive X‐ray spectroscopy analysis verified the quantitative removal of the embedded silica beads. The specific surface areas of the 1, 2, 5 and 10 μm rods were 178, 154, 84 and 125 m²/g after pyrolysis and silica removal, respectively. Shrinkage of the monolithic rods during pyrolysis is proportional to the particle size of the silica used and ranged from 9 to 12%. Mercury porosimetry showed a narrow distribution of pore sizes, with an average of ～700 nm for the 1 μm carbon monolith. The suitability of bare and surface oxidised PCM rods for the use as a stationary phase for reversed and normal phase LC was explored. The additional modification of PCM rods with gold micro‐particles followed by 6‐mercaptohexanoic acid was performed and ion‐exchange properties were evaluated.