Deracemisation and stereoinversion of alpha-amino acids using D-amino acid oxidase and hydride reducing agents

The deracemisation and stereoinversion of both cyclic and acyclic DL-alpha-amino acids, using porcine kidney D-amino acid oxidase (DAAO) and a hydride reducing agent (NaCNBH3-NaBH4), has been investigated.     

Anion sensing 'venus flytrap' hosts: a modular approach

A series of podands based on three hydrogen bonding 'arms' have been prepared and their affinities for simple inorganic anions measured.     

The bromopentadienyl acrylate approach to himbacine

[reaction: see text] The syntheses of 4,4a-didehydrohimbacine and 4,4a-didehydrohimandravine are presented. Key steps include an intramolecular Diels-Alder reaction of a bromopentadienyl acrylate and Suzuki-Miyaura and Stille coupling reactions.     

Extremely low vertical-emittance beam in the accelerator test facility at KEK

Electron beams with the lowest, normalized transverse emittance recorded so far were produced and confirmed in single-bunch-mode operation of the Accelerator Test Facility at KEK. We established a tuning method of the damping ring which achieves a small vertical dispersion and small x-y orbit coupling. The vertical emittance was less than 1% of the horizontal emittance. At the zero-intensity limit, the vertical normalized emittance was less than 2.8 x 10(-8) rad m at beam energy 1.3 GeV. At high intensity, strong effects of intrabeam scattering were observed, which had been expected in view of the extremely high particle density due to the small transverse emittance.     

Confinement-induced entropic recoil of single DNA molecules in a nanofluidic structure

The behavior of DNA molecules is observed in a nanofluidic device near the interface of two regions that produce different configuration entropies. An electric field is applied to drive the molecules partway across the interface. Upon removal of the field, the molecules recoil to the higher-entropy region with a profile characteristic of a force localized to the interface and independent of length. This is consistent with a confinement-mediated entropic force, distinct from the well-known entropic elasticity common to all polymers. An estimate of the hydrodynamic drag is used to produce a lower bound for the force. The phenomenon can be exploited to separate long-strand polyelectrolytes according to length.     

一种新型的移动增值服务——动态电话簿

今天的手机采用相对简单的接口就可以进行电话呼叫。虽然相对于传统固定电话拨号略微复杂了一些,但是移动电话接口还是包括了内置电话录和其它崭新的功能。然而,通信远不限于语音通话。现在我们的手机上有文本消息、一键通、图像邮件和多用户游戏。而我们的P C电脑支持即时通信     

Comparison of high-temperature-superconductor and metal-basedresonators

A 50-Ω coplanar waveguide (CPW) resonator designed for a fundamental frequency of about 4.75 GHz was fabricated on LaAlO₃ . Two versions were fabricated: the first using 1.9-μm-thick gold and the second using 0.6-μm-thick YBa₂Cu₃O ₇. The devices were identically packaged and tested at 77 K. It was found that the high-temperature superconductor (HTS) resonator had a surface resistance, R_s, about six to nine times lower than the Au one. At 45 K, the R_s of the HTS resonator decreases by another factor of 4 compared with its 77 K value. Device characteristics for the HTS resonator are presented     

A reexamination of forward masking in the auditory nerve

Forward masking, as measured behaviorally, is defined as an increase in a signal's detection threshold resulting from a preceding masker. Previously, forward masking in the auditory nerve has been measured as a reduction in the neural response to a signal when preceded by a masker. However, detection threshold depends on both the magnitude of the response to the signal and the variance of the response. Thus changes in detectability cannot be inferred from response reduction alone. Relkin and Pelli (1987) have described a two-interval forced-choice procedure that may be used to measure the threshold for the detection of a probe signal in recordings of spike counts in single auditory neurons. These methods have been used to study the forward masking of characteristic frequency probe tones by characteristic frequency maskers as masker intensity was varied. Although the masker does reduce the detectability of the probe tone, it was found that the threshold shifts are much less than those observed behaviorally, particularly for intense maskers. In part, the small threshold shifts can be attributed to the reduction in response variance following the masker, which is the result of the adaptation of spontaneous activity. These results imply that behavioral forward masking must result from suboptimal processing of spike counts from auditory neurons at a location central to the auditory nerve.     

Nonblocking multirate distribution networks

Results for nonblocking distribution networks are generalized for the multirate environment in which different user connections share a switch's internal data paths for arbitrary fractions of the total capacity. Conditions under which network proposed by Y.P. Ofman (1965), C.D. Thompson (1978), and N. Pippenger (1973) lead to multirate distribution networks are derived. The results include both rearrangement and wide-sense nonblocking networks. The complexity of the rearrangement multirate network exceeds that of the corresponding space-division network by a log log factor, while the complexity of the wide-sense nonblocking network is within a factor of two of the corresponding space-division network