On the statistical mechanics of the traveling salesman problem

We consider the statistical mechanics of the traveling salesman problem (TSP) and develop some representations to study it. In one representation the mean field theory has a simple form and brings out some of the essential features of the problem. It shows that the system has spontaneous symmetry breaking at any nonzero temperature. In general the phase progressively changes as one decreases the temperature. At low temperatures the mean field theory solution is very sensitive to any small perturbations, due to the divergence of some local susceptibilities. This critical region extends down to zero temperature. We perform the quenched average for a nonmetric TSP in the second representation and the resulting problem is more complicated than the infinite-range spin-glass problem, suggesting that the free energy landscape may be more complex. The role played by frustration in this problem appears explicitly through the localization property of a random matrix, which resembles the tight binding matrix of an electron in a random lattice.     

Charateristics of a helical axial flow CO_2 laser

A novel CO_2 laser tube which forms a helical axial gas flow is designed. The influences of such a flow on the output laser beam is discussed.     

高纯金属镨中痕量稀土杂质的电感耦合等离子体原子发射光谱分析及光谱干扰的校正

本文提出了PGS-2型平面光栅光谱仪(色散率0.18纳米,二级光谱)与PlasmaTherm ICP-5000D射频发生器联用,乙醇预去溶方式进样,同时直接测定高纯金属镨中5个痕量稀土杂质元素的方法。并讨论了基体浓度对检出限的影响以及光谱干扰及其校正方法。当样品溶液中镨的浓度为5毫克/毫升时,测定下限分别为镧、钕和钐0.002%,铈0.003%和钇0.0005%。获得了良好的实验结果,其相对标准偏差为1.2-6.2%。     

Investigation of unique hue setting changes with ageing

Clromatic sensitivity along the protan, deutan, and tritan lines and the loci of the unique hues (red, green, yellow, blue) for a very large sample (n = 185) of colour-normal observers ranging from 18 to 75 years of age are assessed. Visual judgments are obtained under normal viewing conditions using colour patches on self-luminous display under controlled adaptation conditions. Trivector discrimination thresholds show an increase as a function of age along the protan, deutan, and tritan axes, with the largest increase present along the tritan line, less pronounced shifts in unique hue settings are also observed. Based on the chromatic (protan, deutan, tritan) thresholds and using scaled cone signals, we predict the unique hue changes with ageing. A dependency on age for unique red and unique yellow for predicted hue angle is found. We conclude that the chromatic sensitivity deteriorates significantly with age, whereas the appearance of unique hues is much less affected, remaining almost constant despite the known changes in the ocular media.     

Incompressible quantum liquids and new conservation laws

In this Letter, we investigate a class of Hamiltonians which, in addition to the usual center-of-mass momentum conservation, also have center-of-mass position conservation. We find that, regardless of the particle statistics, the energy spectrum is at least q-fold degenerate when the filling factor is p/q, where and are coprime integers. Interestingly, the simplest Hamiltonian respecting this type of symmetry encapsulates two prominent examples of novel states of matter, namely, the fractional quantum Hall liquid and the quantum dimer liquid. We discuss the relevance of this class of Hamiltonian to the search for featureless Mott insulators.     

Spontaneous polarization in one-dimensional Pb(ZrTi)O3 nanowires

Formation of spontaneous polarization in one-dimensional (1D) structures is a key phenomenon that reveals collective behaviors in systems of reduced dimensions, but has remained unsolved for decades. Here we report ab initio studies on finite-temperature structural properties of infinite-length nanowires of Pb(Zr0.5Ti0.5)O3 solid solution. Whereas existing studies have ruled out the possibility of phase transition in 1D chains, our atomistic simulations demonstrate a different conclusion, characterized by the occurrence of a ferroelectric polarization and critical behaviors of dielectric and piezoelectric responses. The difference is accounted for by the use of depolarizing effects associated with finite thickness of wires. Our results suggest no fundamental constraint that limits the use of ferroelectric nanowires and nanotubes arising from the absence of spontaneous ordering.     

纳米TiO2∶Zn薄膜电极紫外光电特性研究

采用sol-gel法制备了Zn2+掺杂的锐钛矿相纳米TiO2薄膜电极.通过光电流作用谱和电流-电位（I-U）曲线研〖WTBZ〗究了掺杂不同浓度Zn2+的TiO2薄膜电极的光电特性.由光电流作用谱可知，Zn2+的掺杂可显著影响薄膜电极的光电流大小，且掺杂的最佳浓度与薄膜晶粒尺度有关.在320nm单色光照射下，掺杂浓度（摩尔浓度）为0.1％的薄膜电极光电流最大，与未掺杂的本征薄膜电极相比增幅达40％.I-U曲线表明，光照下，随电极电位由正到负逐渐降低，不同掺杂浓度的TiO2薄膜电极中均出现了阳极电流向阴极电流转换的现象，且Zn2+掺杂浓度可影响电极阳极电流的初始电位.另外，无光照的暗态下，各薄膜在负电位区域观察到了相似的随电位降低而迅速增大的阴极暗电流.