Triggering and guiding of an upward positive leader from a ground rod with an ultrashort laser pulse. I. Experimental results

Using a plasma channel produced by an ultrashort laser pulse, we have studied the laser triggering and guiding of a positive leader from the tip of a 2-m vertical rod standing on the bottom plane of a 7-m plane-plane gap. The purpose of this setup was to reproduce in the laboratory the electric field conditions leading to the onset of a positive upward leader from a ground rod as a downward negative leader is approaching during a thunderstorm, in order to demonstrate the working principle of a possible future laser lightning rod. The leader triggering properties of the laser-created plasma channel have been studied as a function of the synchronization of the laser pulse with the voltage impulse applied to the gap. We show that the laser pulse reduces the inception voltage of the leader compared to its normal value and that the laser plasma channel guides the propagation of the upward leader at a velocity ten times higher than that of an ordinary leader, with a significantly lower charge per unit length. We show that laser guiding of the leader significantly reduces the breakdown voltage of the gap and that the effect of the laser channel at the end of a lightning rod can be compared quite favorably with the effect of an additional metal rod of the same length.     

Skill Requirements for the Rehabilitation Engineer: Results of a Survey

A survey of skills requred for rehabilitation engineering was prepared by the Biomedical Engineering Divison of the American Society for Engineering Education. The purpose of the survey was to determine basic and specific skills needed for the practice of rehabilitation engineering as assessed by four groups: biomedical engineering educators, practicing engineers, medical doctors, and medical specialists. Results indicated an emphasis in basic skills such as transducers, medical devices, kdnesiology, and anatomy, and in specific skills such as rehabilitation devices and aids, equipment control programs, and legal correlates. The two engineering groups tended to agree with each other as did the two medical groups; however, the engineeringgroups did not always concur with the medical groups. Medical doctors and medical specialists generally desired a more broadly trained and more highly skilled rehabilitation engineer. Results suggest that the M.S. degree level appears most reasonable for educational training in rehabilitation engineering.     

Quantification of Hand Tremor in the Clinical Neurological Examination

A compensatory tracking task using a visual display and augmented auditory feedback and requiring subjects to maintain a 500-gm force on a control stick has been modified for clinical use. Integrated absolute values of the subjects' force error/second (tremor scores) have been used as a measure of steadiness, and power spectra of the force error have been used to establish the predominant tremor frequencies. Twenty parkinsonian patients, 7 age-matched controls, and 20 young controls have been evaluated, and representative tremor-time records, tremor scores, and tremor-power spectra are presented. The quantitative measures have proven sensitive to individual differences among normals, yet having a dynamic range sufficient to include the most severely afflicted patient tested. Normative values of both tremor scores and predominant tremor frequencies have been established and are significantly different from the parkinsonian values, the parkinsonian patients having a higher average tremor score [8.31 versus 3.76 (gram . seconds/second)] and a lower mean predominant tremor frequency (6.6 Hz versus 7.9 Hz). Representative tremor-power spectra have proven useful in describing physiological and parkinsonian tremors. Reevaluation over 1-3-week intervals indicates that the quantitative measures of tremor scores are reliable (r= 0.83, p < 0.01 for control subjects; r = 0.87, p < 0.01 for parkinsonian patients). In addition, the predominant tremor frequency as measured from the tremor-power spectra is found to be independent of learning effects. It is emphasized that such tests are not designed as diagnostic tools in themselves.     

Fractal aggregates in simulated reduced gravity

We have developed a study of fractal aggregates in the laboratory geared towards their final production in a microgravity environment, on board of space shuttles and stations. Floating particles in gases and fluids have allowed simulation of conditions in reduced gravity. Production methods and dimensional analysis are described.     

Fusion cross section for 13C + 13C at low energies

The energy dependence of the fusion cross section has been measured over the range E_c.m. = 3.05–6.88 MeV by detecting the γ-rays from residual nuclei in a 4π geometry. Analyzing the 1.37 MeV photopeak, originating from ${}^{24}\text{Mg}\text{1.37}\text{MeV}\text{→}\text{g.s. transition}$, the cross sections for ²⁴Mg+2n channel were also deduced. The measured fusion cross sections have been compared with those for ¹²C + ¹²C and ¹²C + ¹³C systems and found to be significantly different. For ¹³C+¹³C the fusion cross sections agree with the standard optical-model prediction down to the lowest measured energies, while for ¹²C + ¹²C and ¹²C + ¹³C they are, at the lowest energies, too low. It is suggested that the unpaired valence nucleons facilitate fusion at energies well below the Coulomb barrier.     

Structurally diverse aggregating condensations of Ti(IV) catecholates

The simple 1:1 reaction of naphthalene-2,3-diol (H2Np) with Ti(OiPr)4 has a complicated outcome, one rich in diversity and elucidated in this paper by X-ray crystallography and NMR spectroscopy. The reaction in CDCl3 produces a crystalline precipitate, which was found to be the symmetrical dimer [TiNp(OiPr)2]2(HOiPr)2 whose coordinated HOiPr units are hydrogen bonded to OiPr groups (A). A second crystal was also harvested and found to be a partially hydrolyzed 6:6 assembly [Ti3(mu3-O)(mu-Np)2(Np)(mu-OiPr)(OiPr)(HOiPr)2(mu-O)]2 (B) constructed of mu-oxo-linked inverted halves, each a 3:3 assembly anchored by a mu3-oxo group. The supernatant was deduced to contain a soluble 3:3 product [TiNp(OiPr)2]3(HOiPr) possessing the same stereochemistry as B and its likely hydrolysis precursor. When A was redissolved, it produced what appeared to be a 4:4 condensation product, which was also present in the supernatant when the reaction was conducted in the presence of HOiPr-absorbing 13X molecular sieves, or when the reaction mixture was heated. In an analogous reaction, Ti(OtBu)4 produced only an A-like dimeric product possessing pentacoordinate metal centers.     

A dynamic vehicle routing problem with multiple delivery routes

This paper considers a vehicle routing problem where each vehicle performs delivery operations over multiple routes during its workday and where new customer requests occur dynamically. The proposed methodology for addressing the problem is based on an adaptive large neighborhood search heuristic, previously developed for the static version of the problem. In the dynamic case, multiple possible scenarios for the occurrence of future requests are considered to decide about the opportunity to include a new request into the current solution. It is worth noting that the real-time decision is about the acceptance of the new request, not about its service which can only take place in some future routes (a delivery route being closed as soon as a vehicle departs from the depot). In the computational results, a comparison is provided with a myopic approach which does not consider scenarios of future requests.     

Genetic algorithms for the traveling salesman problem

This paper is a survey of genetic algorithms for the traveling salesman problem. Genetic algorithms are randomized search techniques that simulate some of the processes observed in natural evolution. In this paper, a simple genetic algorithm is introduced, and various extensions are presented to solve the traveling salesman problem. Computational results are also reported for both random and classical problems taken from the operations research literature.