Synthesis of β-phenyl-δ,ε-unsaturated amino acids and stereoselective introduction of side chain groups into [4,3,0]-bicyclic β-turn dipeptides

(2S,3S)- and (2R,3R)-2-amino-3-phenyl-5-hexenoic acids have been synthesized in large scale by using Ni(II)-complexes as a template. The amino acids were used in the synthesis of [4,3,0]-bicyclic β-turn mimetics by a convergent methodology. The unique advantage of this strategy is the convenience of introducing side chain groups with predetermined chiralities on both the five- and six-membered heterocyclic rings.     

Relaxor behavior of (Ba,Sr)(Zr,Ti)O3 ferroelectric ceramics

We examine the ferroelectric-relaxor behavior of (Ba_0.65Sr_0.35)(Zr_0.35Ti_0.65)O₃ (BSZT) ceramics in the temperature range from 80 to 380 K. A broad dielectric maximum, which shifts to higher temperature with increasing frequency, signifies the relaxor-type behavior of these ceramics. The value of the relaxation parameter γ∼2 estimated from the linear fit of the modified Curie-Weiss law, indicates the relaxor nature of the BSZT ceramics. The dielectric relaxation rate follows the Vogel-Fulcher relation with T_VF=107 K, E_a=0.121 eV, and ν₀=6.83×10¹⁴ Hz, further supports such relaxor nature. The slim P-E hysteresis loop and ‘butterfly’ shape dc bias field dependence of permittivity at T>T_m (T_m, the temperature of permittivity maximum) clearly signifies the occurrence of nanopolar clusters, which is the typical characteristic of ferroelectric relaxor. At 300 K and 10 kHz, the dielectric constant and loss tan δ are ∼1100 and 0.0015, respectively. The high tunability (∼25%) and figure of merit (∼130) at room temperature show that the BSZT ceramics could be a promising candidate for tunable capacitor applications.     

完全Rees矩阵半群的分解及性质

用等价关系Q^~出了完全Rees矩阵半群的一种分解．而且得到了它的每个Q^~一类的表示．     

An alternative method to compute the component fractions in the geometrical optical model: visual computing method

A method called visual computing was used to solve angular four-components' proportions and directional vegetation cover fraction for discrete canopies and continuous row-planted plants. It proved effective to predict the angular characteristics on pixel scale. The method could be an alternative way to a classical solution of geometrical optical models. A visual computing method would be effective especially when the canopies' spatial distribution and shapes were irregular and could not be described statistically.     

A broadband PHEMT MMIC distributed doubler using high-pass drain line topology

A broadband frequency doubler, based on distributed amplifier techniques, has been designed to operate from 11 to 21 GHz. In order to reject the fundamental signal over a broadband frequency range, the conventional low-pass drain line structure was replaced with the high-pass structure. This topology can suppress fundamental signals over broadband without any balanced structure so that the chip size can be more compact. Measured conversion losses of better than 10 dB from 11 to 21 GHz input frequencies are achieved with fundamental signal rejection better than 12 dB. To the best of our knowledge, this is the first demonstration of distributed doubler using the high-pass drain line topology.     

20-relative neighborhood graphs are hamiltonian

For any two points p and q in the Euclidean plane, define LUN_pq = { v | v ∈ R², d_pv < d_pq and d_qv < d_pq}, where d_uv is the Euclidean distance between two points u and v . Given a set of points V in the plane, let LUN_pq(V) = V ∩ LUN_pq. Toussaint defined the relative neighborhood graph of V, denoted by RNG(V) or simply RNG, to be the undirected graph with vertices V such that for each pair p,q ∈ V, (p,q) is an edge of RNG(V) if and only if LUN_pq (V) = ?. The relative neighborhood graph has several applications in pattern recognition that have been studied by Toussaint. We shall generalize the idea of RNG to define the k-relative neighborhood graph of V, denoted by kRNG(V) or simply kRNG, to be the undirected graph with vertices V such that for each pair p,q ∈ V, (p,q) is an edge of kRNG(V) if and only if | LUN_pq(V) | < k, for some fixed positive number k. It can be shown that the number of edges of a kRNG is less than O(kn). Also, a kRNG can be constructed in O(kn₂) time. Let E_c = {e_pq| p ∈ V and q ∈ V}. Then G_c = (V,E_c) is a complete graph. For any subset F of E_c, define the maximum distance of F as max_epq∈Fd_pq. A Euclidean bottleneck Hamiltonian cycle is a Hamiltonian cycle in graph G_c whose maximum distance is the minimum among all Hamiltonian cycles in graph G_c. We shall prove that there exists a Euclidean bottleneck Hamiltonian cycle which is a subgraph of 20RNG(V). Hence, 20RNGs are Hamiltonian.     

CO2激光器线偏振光输出腔内起偏器的研究

混合InGaAs光电二极管阵列ETX128FPA是16384元InGaAs焦平面阵列,供1.0～1.7μm波段内的近红外成象使用。这种128×128元的二维光电二极管阵列是使用钢冲击结合技术把InGaAs材料结合到高级的CMOS倍增管上而制成的。     

Reactivity of 3-alkyl-4-arylazomethylene-3,4-dihydro-1,2,3-benzotriazines in protic solvents: 1,4-Addition reactions and dimroth rearrangement

3-Alkyl-4-arylazomethylene-3,4-dihydro-1,2,3-benzotriazines 5a and 5b undergo facile 1,4-addition of methanol or ethanol to afford stable crystalline hydrazones, 6 and 8 which have been characterised by spectroscopic analysis. In particular, the nmr spectrum of 8 shows novel features due to the diastereotopic nature of the CH₂ protons in the two O-ethyl groups. Compound 5b shows a property unique to the compounds in this series; refluxing this arylazomethylenetriazine in ethanol affords a rearranged product, characterised as the 1-aryl-2-cinnolinylhydrazine ( 9 ). The formation of 9 is rationalised as a ring opening-ring closure process analogous to the Dimroth rearrangement. The cinnoline 9 displays some novel chemistry arising from the facility of the arylhydrazino substituent to react with acid to give a fragmentation product, 3-methylindazole ( 7 ).     

液态铅的电阻率

采用精确的结构因数实验数据和Ｂｅｈａｖｉ模型赝势，用Ｚｉｍａｎ理论计算了液态铅的电阻率．计算结果和实验数据符合很好．讨论了Ｚｉｍａｎ理论对液态铅的适用性以及适合于液态铅的赝势的特征．