The separation of zirconium and hafnium in a molten salt-molten zinc system

The commercial separation of zirconium and hafniumvia aqueous/organic extraction procedures is both difficult and expensive. The principal objective of the present work was to study an alternative procedure involving the oxidation-reduction equilibria of zir-conium and hafnium between a molten salt phase and molten zincvia the displacement reaction: Zr(IV)_{molten salt} + Hf_{molten zink} ⇌ Hf(IV)_{molten salt} + Zr_{molten zink} The reaction goes strongly to the right with an equilibrium constant: logK =0.432 ×10⁴/T - 1.565 for Na₂Zr(Hf)F₆ dissolved in NaKCl₂ solvent, thus showing promise as the basis for an anhydrous process for separating zirconium and hafnium. The rate of approach to chemi-cal equilibrium was studied in a baffled stirred reactor. The equilibration rate was found to be controlled by the hafnium mass transfer rate from the molten zinc to the metal-salt interface. The mass transfer rate could be estimated from the physical properties of the molten metal and the salt phases, using the Mayer correlation. Formerly with the Teledyne Wah Chang Cor-poration, Albany, OR.     

Approximating the Advertisement Placement Problem

The advertisement placement problem deals with space and time sharing by advertisements on the Internet. Consider a Web page containing a rectangular display area (e.g., a banner) in which advertisements may appear. The display area can be utilized efficiently by allowing several small ads to appear simultaneously side by side, as well as by cycling through a schedule of ads, allowing different ads to be displayed at different times. A customer wishing to purchase advertising space specifies an ad size and a display count, which is the number of times their ad should appear during each cycle. The scheduler may accept or reject any given advertisement, but must be able to schedule all accepted ads within the given time and space constraints. Each advertisement has a non-negative profit associated with it, and the objective is to schedule a maximum-profit subset of ads. We present a (3 + )-approximation algorithm for the general problem, as well as (2 + )-approximation algorithms for two special cases.     

Decoupling and pole assignment in nonlinear systems

The paper deals with the decoupling of nonlinear time-variable systems by state feedback. The class of systems that can be decoupled is extended, a feedback law in explicit form is given for the pole assignment of the decoupled system and the structure of the compensated form is considered.     

Causes of failure of surgery on the lumbar spine

An interinstitutional study on the failed back surgery syndrome (FBSS) has determined that failure to recognize or adequately treat lateral stenosis of the lumbar spine with resultant nerve irritation and/or compression comprised the primary etiology in 57% to 58% of patients. Other common causes were recurrent or persistent disk herniation and lumbosacral adhesive arachnoiditis. The diagnosis of stenosis was made either by high-resolution CT scan of the lumbar spine or by directly testing lateral canal and for animal patency at the time of surgery. It is now appreciated that the process of degenerative disk disease, particularly when enhanced by diskectomy, results in progressive loss of intervertebral disk volume and predisposes to future ipsilateral or contralateral lateral spinal stenosis. Degenerative disk disease is ultimately a bilateral process and therefore surgical exposure should be bilateral. The direct and indirect costs of FBSS to patients and to society as well as the toll in human suffering are very high. This is particularly a matter of concern when it is realized that for many FBSS patients, surgery could have been avoided in the first place by preventive care or by innovative conservative treatment. When surgery is indicated, adequate diagnostic tests and the execution of appropriate procedures based upon this information should largely prevent the failed back surgery syndrome.     

Me against myself: Motivational conflicts and emotional development in adulthood.

Two studies investigated adult age differences in the frequency and emotional consequences of motivational conflicts (i.e., feeling that one wants to or should do something else in a given situation). Study 1 compared younger and older adults. Study 2 included a more age-heterogeneous sample ranging from 20 to 70 years. Data were obtained using diary and experience-sampling methods. Multilevel regression showed that motivational conflict was associated with lower emotional well-being. With age, the frequency of motivational conflict decreased, while emotional well-being increased. Importantly, the age-related decrease in motivational conflicts partly accounted for the age-related increase in emotional well-being. Findings were consistent across studies and robust after the authors controlled for age differences in a number of control variables including time use. The authors conclude that an age-related decrease in motivational conflicts in daily life may be among the factors underlying the positive development of emotional well-being into older adulthood. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Multiple signal representation simulation of photonic devices,systems, and networks

Photonic systems design requires simulation over a wide range of scales; from wavelength-sized resonances in lasers and filters, to interactions in global networks. To design these global systems, while considering the effects of the smallest component, requires sophisticated simulation technology. We have developed the Photonic Transmission Design Suite, which includes five different signal representations, so that the details of device performance can be efficiently considered within a large network simulation. Alternatively, a design can be studied using a coarse signal representation before switching to a detailed representation for further refinement. We give examples of the application of these representations, and show how the representation of a signal is adapted as it propagates through a system to optimize simulation efficiency     

Determination of the coherent scattering length of carbon using neutron interferometry

Highly oriented pyrolytic graphite samples were used for determining the coherent scattering length of the bound carbon atom by means of neutron interferometry. The value of 6.647±0.005 fm agrees well with results obtained by various other techniques.     

卟啉类L—B膜分子间相互作用的光谱研究

以无取代的meso-四-(4-N)-吡啶基卟啉及其过渡族金属(主要Cu~(2+)、Zn~(2+))络合物制备L-B膜,以近紫外-可见吸收光谱和荧光光谱为手段,研究叶啉类分子在氯仿溶液中,L-B膜状态下以及固态状态下的相互作用。探讨分子聚集体的存在对光谱性质的影响。 为了研究叶咻类分子间的相互作用及其对光谱性质的影响,我们首先分析了叶啉在CHCl_3溶液中及固态状态下的近紫外-可见吸收光谱和荧光光谱。并将其与叶啉类分子的L-B膜作比较。结果表明,卟啉类的Soret吸收带带宽及峰位置在三种状态下均不相同,L-B膜的情况介于溶液中的和固体下的情况之间,说明了在L-B膜中,卟啉分子存在着某种形式的聚集体,且在这种聚集体中分子间的相互作用程度比固体弱,可以认为L-B膜上的分子呈准晶体状态。