Polarization in Pseudoscalar Meson Photoproduction

Two problems of current interest in the use of polarization observables for pseudoscalar meson photoproduction to probe the basic dynamics are discussed. The first one concerns the extraction of the ratio of electric quadrupole to magnetic dipole transition strengths in the photo-excitation of the . The predictions of various models are compared with the recent LEGS and MAMI data obtained with polarized photon beams. The second one is a proposal by Saghai and Tabakin to use the nodal structure of spin observables to unveil underlying dynamics in the production process. We demonstrate with the example of at photon energy that the assumption of multipole truncation, which enters into their nodal analysis, is questionable. Received October 11, 1997; revised February 16, 1998; accepted for publication March 6, 1998     

Hybrid-conventional finite element for gradient-dependent plasticity

The hybrid-conventional finite element method is applied to the analysis of quasi-static, gradient-dependent elastoplastic problems in solid mechanics. The stresses within the element domain and the displacements on the boundary are simultaneously and independently approximated using Trefftz constraints, which lead to boundary integrals. The plastic multipliers are conventionally approximated with regard to C₀ continuity of the multiplier field of the gradient-dependent plasticity. The finite element formulation is derived using a Galerkin-weighted residual approach. The plastic boundary conditions are examined and plastic radiations are set to zero on the plastic boundaries. The effectiveness of the present method is demonstrated with three numerical applications.     

Ferroelectric liquid crystal materials synthesized from 2(S)-[2(S)-methylbutyloxy]propanol

A new chiral alcohol, 2(S)-[2(S)-methylbutyloxy]propanol (3), containing two chiral centres has been synthesized from ethyl lactate and (S)-1-iodo-2-methylbutane. It was used as a chiral building block for the preparation of ferroelectric liquid crystal materials. Several of the new materials exhibit an enantiotropic S*_c phase with a wide temperature range. The results indicate that the molecular structure of 3 is useful for synthesizing ferroelectric liquid crystal materials.     

Comparison of three solvers for viscoelastic fluid flow problems

The computational efficiency of three numerical schemes has been examined for the solution of a linearized system of equations resulting from the finite element discretization of a viscoelastic fluid flow problem. The first scheme is a modified frontal solver, which solves the linear system of equations directly. The other two, one based on a biconjugate gradient stabilized (BiCGStab) method and another based on a generalized minimal residual (GMRES) method, are iterative schemes. The stick-slip problem and the four-to-one contraction problem were analyzed and the viscoelastic fluid was assumed to obey the Oldroyd-B model. The two iterative schemes are superior to the direct scheme in terms of CPU time consumed and the BiCGStab scheme is even faster than the GMRES scheme. The range of convergence for both iterative schemes is compatible with that of the direct scheme.     

Towards Bounding Complexity of a Minimal Model

We give some effectivity results in birational geometry. We provide an upper bound on the rational constant in Rationality Theorem in terms of certain intersection numbers, under an additional condition on the variety that it admits a divisorial contraction. One consequence is an explicit bound on the number of certain extremal rays. Our main result tries to construct from a given set of ample divisors H _j on X with their intersection numbers b _i , a certain set of ample divisors L _j on X' or X ⁺ where X' or X ⁺ arises from a contraction or a flip,such that the corresponding intersection numbers of L _j are uniformly bounded in terms of b _i and the index of X. This gives a bound on the projective degree of a minimal model in special case.     

The “Qualitative” Differences in Problem-Solving Procedures and Thinking Structures Between Science and Nonscience Majors

This study was conducted to explore the differences of problem-solving procedures and thinking structures between science majors and nonscience majors. A total of eleven Chinese graduate students, consisting of 5 science majors and 6 nonscience majors, participated in this study and completed the same task. The interview data showed us that: (1) Nonscience majors began with personal experience questions whereas science majors promptly designed an experiment; (2) Nonscience majors tended to confirm expected answers whereas science majors tended to explore some questions with unknown answers; (3) Nonscience majors preferred to process the procedures by creating the plan mentally in advance, whereas science majors preferred to proceed by doing, adjusting the plan as the procedures progressed; (4) Science majors would consider the assumption and the validity of the test whereas nonscience majors rarely did; and (5) Nonscience majors were curious about how they would fare if given the same testing situation whereas science majors completed only the required task. Further discussion revealed that the reasoner's epistemology or academic experiences might strongly influence these problem-solving processes, thinking and actions. The implications of this study for improving current curriculum design were discussed.     

Antiferroelectric liquid crystals derived from a new optically active (R)-3-ethylmercapto-2-methylpropionic acid

A new optically active (R)-3-ethylmercapto-2-methylpropionic acid has been synthesized using D(-)—2,10-camphorsultam as a chiral auxiliary. The optical purity of the acid obtained was greater than 98 per cent. Its derivatives, (R)-4-(3-ethylmercapto-2-methylpropionyl)phenyl 4'-alkoxybiphenyl-4-carboxylates (EMMPPmBC; m = 7-16), have been prepared for the investigation of liquid crystalline properties as a function of peripheral alkyl chain length. Optical studies showed that all members exhibited an antiferroelectric S*c_A phase. The results also indicate that a lengthened alkyl chain length is favoured for S_cA* phase formation.     

A model for establishing the ultimate enhancements (A∞) in the low to high magnetic field transfer dynamic nuclear polarization experiment

In a preliminary report, we have demonstrated transfer of a flowing bolus enhanced in low magnetic fields (e.g., 0.33 T) with dynamic nuclear polarization (DNP), but monitored in a high magnetic field (4.7 T). The advantages of the high magnetic field monitoring approach include: 1) greater chemical shift dispersion, and 2) improved signal strength in comparison with static low field DNP experiments. In the present study, a model is developed to predict ultimate DNP enhancements (A_∞) in this experiment for flow liquid/liquid intermolecular transfer (L²IT). L²IT¹H and¹³C data is obtained for benzene and chloroform in order to test the validity of the model. The ultimate¹H and¹³C DNP enhancements obtained for benzene/TEMPO are ?150 and ?220, respectively. For a chloroform/TEMPO (L²IT) sample, the ultimate enhancements are close to the¹H dipolar (?330) and the¹³C scalar (+2660) limit, respectively. In the latter case, the observed¹³C DNP enhancement exceeds the thermal Boltzmann magnetization at 4.7 T by a factor of 21. For a 1-chlorobutane/TEMPO sample selective enhancements were observed at different sites in the molecule. For example, the C-1 carbon exhibits a large scalar enhancement, whereas, the other carbons exhibit dipolar enhancements. Data illustrating the importance of three-spin effects in¹³C DNP studies is also presented. Alternative methods of sample transfer from the low to high magnetic field are also discussed.