Search

Objective We sought to evaluate whether the presence of condition-specific obstetric protocols within a hospital was associated with better maternal and neonatal outcomes. Study Design This was a cohort study of a random sample of deliveries performed at 25 hospitals over 3 years. Condition-specific protocols were collected from all hospitals and categorized independently by 2 authors. Data on maternal and neonatal outcomes, as well as data necessary for risk adjustment were collected. Risk-adjusted outcomes were compared according to whether the patient delivered in a hospital with condition-specific obstetric protocols at the time of delivery. Results Hemorrhage-specific protocols were not associated with a lower rate of postpartum hemorrhage or with fewer cases of estimated blood loss >1000 mL. Similarly, in the presence of a shoulder dystocia protocol, there were no differences in the frequency of shoulder dystocia or number of shoulder dystocia maneuvers used. Conversely, preeclampsia-specific protocols were associated with fewer intensive care unit admissions (odds ratio, 0.28; 95% confidence interval, 0.18–0.44) and fewer cases of severe maternal hypertension (odds ratio, 0.86; 95% confidence interval, 0.77–0.96). Conclusion The presence of condition-specific obstetric protocols was not consistently shown to be associated with improved risk-adjusted outcomes. Our study would suggest that the presence or absence of a protocol does not matter and regulations to require protocols are not fruitful.

Federal regulation of insider trading occurs through three main sources: Section 16 of the Securities Exchange Act of 1934, Securities and Exchange Commission (SEC) Rule 10b-5, and SEC Rule 14e-3. Keywords: insider trading law

The basic concept underpinning much of the US federal securities regulation is disclosure regulation. Keywords: regulation of US equity markets

[Vinylidene-3H] (−)-α-Kainic acid was prepared by means of a Wittig reaction with a protected ketone precursor and has proved useful as a tool to study neuroexcitatory amino acid receptors. Copyright © 2002 John Wiley & Sons, Ltd.

The tritiation of the nightshade alkaloids dihydrocapsaicin, atropine and nicotine is described.

In this study, we examine the relationship between the liquidity of equity and its market value. We find that creating liquid equity claims on relatively illiquid property assets increases value by 12‐22%. However, the fixed costs associated with creating these claims offset these liquidity gains for pools of assets below $100 million. We also estimate that the liquidity of individual properties adds 16% to their value relative to a notional nontradable property asset. Managers can enhance the liquidity of equity and, therefore, the benefits of securitization by increasing size, focus, and institutional ownership. In his seminal article, Coase (1937) addresses the fundamental question of why the corporation exists and prospers as an organizational form. Given that there are significant costs to forming a public corporation, including the cost of a management team and reporting costs, what benefits to public trading outweigh these costs? Coase and many authors that followed concentrate on identifying advantages along the dimensions of reducing contracting, monitoring, and agency costs. However, another branch of the financial economics literature has examined an alternative benefit of the publicly traded corporation: namely, the enhancement of the liquidity of the claims on the assets. Under this paradigm, a firm is viewed as a collection of illiquid assets arising from capital budgeting decisions. Bundling these assets into a corporation and issuing comparatively liquid publicly traded claims to these assets can create value if liquidity is priced.

The thermo-mineral water resources of the Lower Adour, exploited in the "Landes" Department of Southwest France, occur in deep, folded and faulted sedimentary rocks cut through by salt diapirs, part of the Pyrenean foreland structures. The impact of drawing off water for thermal springs, drinking water, geothermal energy, irrigation and for industry, combined with the occupation of underground space for gas storage, generates conflicts in terms of usage. In order to gauge the thermal and salinity effects and to be able to compare the various piezometric measurements within the same hydrodynamic frame of reference, a calculation using an equivalent sweet water load has been undertaken. It shows that in the Dax region there exists a major virtual piezometrie "sink" where, despite this, thermal effects enable waters to rise. This "sink" represents a particularly sensitive area. It is thus proposed to set up a protection zone, establish a steering committee, management procedures and the necessary actions to bring together the various parties concerned with the objective of organising resource exploitation fulfilling the temperature and quality demands of all users.

This study investigates why externally advised real estate investment trusts (REITs) underperform their internally managed counterparts. Consistent with previous studies, we find that REITs managed by external advisors underperform internally managed ones by over 7 percent per year. Property-level cash-flow yields are similar between the two managerial forms, but corporate-level expenses and especially interest expenses are responsible for lower levels of cash available to shareholders in externally advised REITs. We document that the higher-interest expenses are due to both higher levels of debt and to higher debt yields for externally advised REITs. We posit that compensating managers based on either assets under management or on property-level cash flows creates incentives for managers to increase the asset base by issuing debt even if the interest costs are unfavorable.

We trace the effects of corporate focus by examining the relationships among focus, cash flows and firm value. In contrast to past studies that examine the effects of diversifying across SIC-code-defined industries, we show that diversification, even within a single industry, reduces value. Our evidence, drawn from a panel of real estate investment trusts, indicates that this reduction is not due to poor managerial performance. Project-level cash flows are actually higher for less focused firms. However, these gains are offset by higher management, administrative and interest expenses. Thus, the corporate cash flows available to shareholders are not related to focus. Finally, we provide empirical evidence that links the effect of focus on value to informational asymmetries which cause the equity of diversified firms to be less liquid. We attribute some of the effect of focus on the cost of both debt and equity to informational asymmetries or transparency costs.

The paper presents a novel method of utilising neural networks for optimisation systems. First, a conventional magnetic circuit model of the device is developed to create a set of sensitivity rules which guide the optimisation. The rules are coded in a knowledge‐based neural network. Second, an error network is developed to correct the approximations inherent in the magnetic circuit approach and this combines with the first network to generate realistic outputs. Finally, the error network can be trained on‐line with a finite element system. Over time, the network replaces the finite element analysis, thus speeding up the optimisation process.

This paper presents analytical solutions for estimating the potential impact of waste disposal sites (landfills) on ground water. The solutions yield estimates of the average groundwa ter concentrations in an aquifer located below the landfill, and of the pollutant flux at the interface between a mineral barrier and the aquifer. Several source boundary conditions are considered: a constant source concentration, an exponen tially decreasing source concentration, and a source concen tration that is controlled by the diffusive release of pollutants from the waste. The latter is of particular relevance to the case of stabilized-waste landfills. The solution for the case of stabilized-waste is compared to two numerical models, and developed in terms of dimensionless variables that are combi nations of the real model parameters. These variables are then used to generate type curves for estimating peak aquifer concentrations. An example application of the proposed type curves illustrates their usefulness for evaluating the perfor mance of stabilized-waste landfills, in terms of potential impact, for different landfill designs.

An excitation and optical extraction geometry suitable for compact high power gas lasers is described. Multiple slab discharges are established in a diffusion-cooled radial electrode array. Each gain channel is independently driven from a common RF source via a resonant-cavity power distribution system. Radial excitation augmented with multi-channel self-injection phase locking provides stable optical power extraction at good efficiency. The concept is easily scalable to very high powers while dramatically reducing unit size and cost.

We examine a sample of 5896 stocks listed on Nasdaq between 1974 and 1988 to see whether the price per share has significant statistical power in forecasting subsequent returns and attrition rates. Consistent with anecdotal evidence, we document a higher mortality rate for lower-priced stocks than for higher-priced issues. Surprisingly, mortality is not related to market capitalization. Our results also hold for subsamples partitioned by industry and issue year. On average, investors are not adequately compensated for this additional mortality risk, earning lower risk-adjusted rates of return on portfolios of lower-priced shares than on portfolios of higher-priced shares.

Dopamine receptor ligands N-0923 (1) and (+/-)-threo-methylphenidate (4) have been labeled with tritium at high specific activity, for becoming useful tools to study the dopamine receptor family.

Methods are presented to tritiate the side chain of dopamine.

Resonant cavity techniques have been used to implement a high power source of radio frequency excitation for many parallel laser elements in a simple, compact, and low cost structure. A triode oscillator was designed capable of driving up to 48 independent and dynamic loads by utilizing the unique nature of a resonant cavity to extract multiple outputs via magnetic coupling. Over 25 kW of power has been generated at 80 MHz while driving 8 independent CO2 laser slab geometry gas discharges.

The Samuelson hypothesis implies that the volatility of futures price changes increases as a contract's delivery date nears. In markets where the Samuelson hypothesis holds, accurate valuation of options and related derivatives on futures requires that a term structure of futures volatilities be estimated. We develop a framework for predicting those markets where the hypothesis should be expected to hold. In contrast to a prominent reinterpretation of the hypothesis, we show that clustering of information flows near the delivery date is not necessary. We show instead that the hypothesis will be supported in markets where spot price changes contain a predictable temporary component, and we argue that this condition is much more likely to be supported in markets for real assets than for financial assets. Finally, we provide empirical evidence consistent with our predictions.

A unique way of driving a multi-channel RF excited slab laser is presented. Resonant cavity techniques are employed to provide high power splitting and impedance transformation. Uniform and isolated power division was observed in eight discharge channels, stacked in a radial array, referred to as the Zodiac geometry. Impedance matching networks were not necessary as the RF cavity splitter creates a near ideal voltage source capable of driving any impedance. With 8 out of the 24 electrodes driven in the radial array, optical powers in excess of 1.2 kW have been observed at efficiencies of 12%.

This paper studies expectations of capital appreciation in the housing market. We show that expectations impounded in the rent/price ratio at the beginning of the decade successfully predict appreciation rates, but only if we first control for cross-sectional differences in the quality of rental versus owner-occupied housing. We also demonstrate that observed rent/price ratios contain a disequilibrium component that also has power to forecast subsequent appreciation rates. Finally, we provide evidence consistent with euphoria: participants in housing markets appear to overreact to income growth.

A computational model is used to predict longitudinal excitation uniformity in large-area electrodes for RF-excited CO/sub 2/ lasers. Effects of nonuniform discharge loading along the electrode transmission line are accounted for in the model, as is the dependence of discharge properties on power loading, excitation frequency, gas pressure, and electrode geometry. Predictions of excitation uniformity are tested against measurements of discharge luminosity. Good agreement is demonstrated. Since the model is valid over the range of discharge conditions interesting to slab CO/sub 2/ lasers, it should applicable to the problem of slab electrode optimization.

We investigate the relations between trading volumes and our proxies for information flows and divergences in opinions. We view S&P 500 Index futures' open interest as a useful proxy for divergences of traders' opinions, and find that volumes are higher on days when open interest increases than on days with declines. Volume in individual equities is more closely related to firm-specific information flows, while equity basket volume is more closely associated with market information. This differential impact is greatest for small capitalization stocks where market-wide news has no explanatory power.

Serotonergic agonists buspirone 1 and (+/−)-DOB 4 have been labeled with tritium at high specific activity and have emerged as valuable tools to study the serotonin receptor family.

Beta-funaltrexamine is a unique irreversible antagonist for the mu-opiate receptor and would be useful as a tritiated radioligand. Starting from high specific activity [15, 16-³H] naltrexone, [15, 16-³H] beta-funaltrexamine was synthesized and characterized by means of a two-step reductive amination-acylation process.

A rf excitation system that can drive a gas laser constructed of multiple wide, but narrow‐gap (slab), discharge volumes is presented. Resonant cavity techniques adopted from microwave applications are employed to provide uniform rf power division and impedance matching into each electrode channel. This approach when applied to a large radial array of gain channels can be used to create a very high‐power laser system in an unusually compact package.

Background Cesarean delivery in the second stage of labor is common, whereas the frequency of operative vaginal delivery has been declining. However, data comparing outcomes for attempted operative vaginal delivery vs cesarean in the second stage are scant. Previous studies that examine operative vaginal delivery have compared it to a baseline risk of complications from a spontaneous vaginal delivery and cesarean delivery. However, when a woman has a need for intervention in the second stage, spontaneous vaginal delivery is not an option she or the provider can choose. Thus, the appropriate clinical comparison is cesarean vs operative vaginal delivery. Objective Our objective was to compare outcomes by the first attempted operative delivery (vacuum, forceps vs cesarean delivery) in patients needing second-stage assistance at a fetal station of +2 or below. Study Design We conducted secondary analysis of an observational obstetric cohort in 25 academically affiliated US hospitals over a 3-year period. A subset of ≥37 weeks, nonanomalous, vertex, singletons, with no prior vaginal delivery who reached a station of +2 or below and underwent an attempt at an operative delivery were included. Indications included for operative delivery were: failure to descend, nonreassuring fetal status, labor dystocia, or maternal exhaustion. The primary outcomes included a composite neonatal outcome (death, fracture, length of stay ≥3 days beyond mother's, low Apgar, subgaleal hemorrhage, ventilator support, hypoxic encephalopathy, brachial plexus injury, facial nerve palsy) and individual maternal outcomes (postpartum hemorrhage, third- and fourth-degree tears [severe lacerations], and postpartum infection). Outcomes were examined by the 3 attempted modes of delivery. Odds ratios (OR) were calculated for primary outcomes adjusting for confounders. Final mode of delivery was quantified. Results In all, 2531 women met inclusion criteria. No difference in the neonatal composite outcome was observed between groups. Vacuum attempt was associated with the lowest frequency of maternal complications (postpartum infection 0.2% vs 0.9% forceps vs 5.3% cesarean, postpartum hemorrhage 1.4% vs 2.8% forceps vs 3.8% cesarean), except for severe lacerations (19.1% vs 33.8% forceps vs 0% cesarean). When confounders were taken into account, both forceps (OR, 0.16; 95% confidence interval, 0.05–0.49) and vacuum (OR, 0.04; 95% confidence interval, 0.01–0.17) were associated with a significantly lower odds of postpartum infection. The neonatal composite and postpartum hemorrhage were not significantly different between modes of attempted delivery. Cesarean occurred in 6.4% and 4.4% of attempted vacuum and forceps groups ( P = .04). Conclusion In patients needing second-stage delivery assistance with a station of +2 or below, attempted operative vaginal delivery was associated with a lower frequency of postpartum infection, but higher frequency of severe lacerations.

We use the term structure of futures prices to test whether investors anticipate mean reversion in spot asset prices. The empirical results indicate mean reversion in each market we examine. For agricultural commodities and crude oil the magnitude of the estimated mean reversion is large; for example, point estimates indicate that 44 percent of a typical spot oil price shock is expected to be reversed over the subsequent eight months. For metals, the degree of mean reversion is substantially less, but still statistically significant. We detect only weak evidence of mean reversion in financial asset prices. IN THIS STUDY, WE provide evidence of mean reversion in the prices of several real and financial assets. Rather than examining evidence of ex post reversion using time series of asset prices, we use price data from futures contracts with varying delivery horizons to test whether investors expect asset prices to revert. This approach offers two advantages. First, since futures prices are readily available for many markets, our procedure can be implemented for many assets, including those for which reliable spot price data is elusive. Second, there is little ambiguity as to the source of any mean reversion detected using our method. Subject only to the maintained assumption that the no-arbitrage cost-of-carry condition holds, our test detects mean reversion that is expected to occur in equilibrium, but has no power to detect mean reversion resulting from noise or inefficiencies. Our methodology focuses on relations between price levels and the slope of the futures term structure, defined as the change across delivery dates in the futures prices observed on a given trading date. An inverse relation between prices and the futures term slope constitutes evidence that investors expect mean reversion in spot prices. To illustrate, initially assume there are no

A diagnostic method for high power CO2 laser beams is presented. The technique features imaging of high intensity infrared radiation via the thermally induced luminosity of high velocity charcoal particles contained within an air stream. The method is particularly convenient for determination of focal position, depth of field, beam diameter, and spot size. Variations of these parameters with power level are easily observed utilizing this charcoal powder imaging method. Using this ‘‘real‐time’’ technique, focal spot size and location accuracy are ±0.1 and ±1 mm, respectively. Results are shown to be independent of micro‐particle size within specified limits. As a result, periodic, fine laser‐workpiece adjustment is now cost effective when working with high power lasers.

The beam quality of a diffusion-cooled RF-excited radial-geometry CO/sub 2/-slab-laser array is investigated. The system is shown to negate many of the disadvantages inherent with slab lasers, namely, asymmetric beams, multiple focal spots, and linear polarization. In addition, the effective spot size is reduced as a result of radial stacking of the individual asymmetric but azimuthally distributed, incoherent, output beamlets. A performance demonstration with sheet-metal cutting has produced excellent results in terms of kerf width, depth of penetration, and cut directionality. >

Trading halts increase, rather than reduce, both volume and volatility. Volume (volatility) in the first full trading day after a trading halt is 230 percent (50 to 115 percent) higher than following "pseudohalts": nonhalt control periods matched on time of day, duration, and absolute net-of-market returns. These results are robust over different halt types and news categories. Higher posthalt volume is observed into the third day while higher posthalt volatility decays within hours. The extent of media coverage is a partial determinant of volume and volatility following both halts and pseudohalts, but a separate halt effect remains after controlling for the media effect. IN THE WAKE OF the 1987 market break, a number of commentators, including the Presidential Task Force on Market Mechanisms, recommended the establishment of "circuit breaker" mechanisms. The primary argument supporting circuit breakers (both price limits and trading halts) is that nontrading periods provide an opportunity for normal information transmission in times of market duress. Proponents of circuit breakers claim that, during major price changes there can be a breakdown in the transmission of information between the trading floor and market participants. Therefore, "the primary function of a circuit breaker should be to reinform participants" (Greenwald and Stein (1988), p. 17). By lowering informational asymmetries between traders, halts could permit the orderly emergence of a new consensus price. But would "informative" trading halts succeed? Many academics are openly suspicious of any kind of market interference and assume that trading halts are guilty until proven innocent. Grossman (1990, p. 3), for example, argues that the closing of markets "merely prevents consenting adults from carrying out their desires on the floor of the stock exchange." Not only do halts impose a liquidity cost on traders, but studies suggest that information will not be as

International audience; OBJECTIVE: To describe CSF biomarker profiles in posterior cortical atrophy (PCA), which induces high-order visual deficits often associated with Alzheimer disease (AD) pathology, and relate these findings to clinical and neuropsychological assessment. METHODS: This prospective observational study included 22 patients with PCA who underwent CSF biomarker analysis of total tau (t-tau), phosphorylated tau on amino acid 181 (p-tau181), and amyloid β (Aβ(42)). At group level, the CSF profiles of patients with PCA were compared to those of patients with typical AD and patients with other dementia (OD). Individually, the clinical presentation of patients with PCA was correlated to their CSF profile to assess the predictability of clinical features for diagnosis of underlying AD pathology. RESULTS: At group level, the PCA biomarker profile was not different from that of the AD group, but very different from that of the OD group (p < 0.001). More than 90% of patients with PCA had CSF profiles consistent with AD. All patients with PCA with either isolated higher-order visual deficit (n = 8) or visual deficit associated with memory impairment (n = 11) had CSF profiles consistent with AD. Only one of the 3 patients with PCA with asymmetric motor signs fulfilled biological CSF criteria for AD. CONCLUSIONS: PCA syndrome is usually associated with CSF biomarkers suggestive of AD, as shown by previous neuropathologic studies. This does not apply in case of motor signs suggesting associated corticobasal syndrome. CSF biomarkers help to discriminate AD from non-AD processes associated with this condition.

In West Brae field, 4D seismic was used to identify late stage development targets. In the Flugga reservoir, the 4D seismic imaged the water movements that occurred over a decade of production and highlighted an area to the northwest of the field that remained un-drained or inefficiently swept. Close integration between the 4D interpretation and the understanding of the reservoir dynamic behaviour yielded an infill production target in a compartment of the Flugga reservoir sitting underneath a producing well. Multiple models were generated to explain this compartmentalisation and optimise the well placement. The results of the drilling campaign proved the 4D interpretation and the reservoir dynamic mechanisms.

This study examines price stabilization in new equity issues. Stabilizationtruncates the distribution of post-issue prices at a floor price, lowering the risk of adverse price moves and hence, in a competitive dealer market, reducing the bid-ask spread. Using 1.523 NASDAO-traded firm- commitment initial public offerings issued between 1982 and 1987, we find that spreads narrow when the market price is close to the offer price and stabilization is most likely. Moreover, significant negative returns are documented after the hypothesized termination of stabilizing activities, suggesting that stabilization, and its cessation, affect market prices.

As advancements in laser technology result in higher-power devices, increased thermal loads experienced by resonator optical components generate instabilities in the output beam. Consequently, methods for maintaining and optimizing output-beam parameters are necessary for efficient long-term operation. This study examines a vision-based feedback control system which monitors a sampled cross-sectional image of the laser's output, and regulates both cavity mirrors, as well as the excitation level, to stabilize beam uniformity, beam steer, and output-power level. The system optimizes the output-power distribution achievable from a given laser, while significantly reducing beam steering effects. Direction of beam propagation is restricted to within 60 μrad of the desired setpoint, while the output power is stabilized to within 4%. Results clearly document a considerable improvement in laser performance through maximization of beam uniformity, minimization of beam steering, and stabilization of total output power. As such, an important degree of consistency and repeatability in output-beam parameters, essential to precision laser applications, is easily achieved. Valuable diagnostic capabilities pertaining to output beam intensity and energy profiles are also incorporated into the control system. These data may be monitored on-line or stored for subsequent analysis.

As power levels of industrial lasers increase, effective determination of beam profiles over extended operational regimes becomes problematic, due to dynamic range limitations of available detectors. To address this deficiency, a variable coupling rotating wand was developed for on‐line monitoring of output radiation from high average power CO2 lasers. The concept features real‐time beam sampling adjustment, activated by wand rotational speed change. An associated controller provides appropriate speed regulation of the wand motor drive, via a computer generated setpoint. Design parameters thereby ensure optimal sensor operation at all power levels. A safety override prevents sensor damage by terminating laser operation, if wand speed decreases below a safe value.

Many major developed countries, including Germany, Japan and the United Kingdom, have some form of tax on securities transactions. The Clinton administration recently considered imposing fees of from 14? on transactions in futures contracts. Past budgets have considered fees of from 6? to 15?. Proponents of a securities transaction tax in the U.S. argue that it would tap into a significant source of revenues and would, in addition, act to reduce "excess" volatility in securities markets by discouraging speculative and "noise" trading. Some have argued that it would also increase investors' expected holding periods, hence encourage corporate managers to build for the long term. Opponents argue that any benefits from such a tax would be overwhelmed by its costs. They point out that a tax on transactions would increase the cost of capital, reduce market liquidity and bring down security values. Furthermore, as the tax would change the relative costs of holding and issuing different classes of securities, it might be expected to change capital structures and investment portfolios, too. At its worst, a securities transaction tax could drive trading in some securities to overseas markets not burdened by taxation. The economic and societal distortions resulting from taxation and avoidance would likely be large.

The incorporation of a retroreflecting, pseudoconjugating cone as a folding element in a double‐pass unstable resonator of a high‐power carbon dioxide oscillator–amplifier is presented. The concept, when implemented with a truncated cone, has yielded significant improvements in optical energy extraction efficiency, beam quality, and alignment stability. The performance of such a modified clear aperture cone resonator, in comparison with a standard roof prism cavity geometry, is discussed.

Following the crash of 1987, one contentious regulatory issue has been whether margin activity exacerbated the decline in equity values. We contrast the crash behavior of NASDAQ securities eligible for margin trading with the behavior of ineligible ones. Consistent with the hypothesis that margin-eligible securities were more frequently subjected to margin calls and forced sales, we find that abnormal volumes were uniformly larger for eligible securities. However, there is no evidence that this activity provoked additional price depreciation. Margin-eligible securities actually fell by one percent less than the ineligible securities over the period.

Control of frequency and amplitude of the impulses used in photoinitiated, impulse‐enhanced, electrically excited laser pumping determines the E/p value of the discharge. This occurs through the influence of these impulses on the processes of electron density decay and ion‐electron recombination and dissociative attachment. The degree of attachment can be controlled through the use of high‐frequency excitation (f≳10 kHz), while the relative importance of ion‐electron recombination increases with increasing impulse potentials. The reduced electric field E/p can thus be varied by a factor of 3, while the anode fall potential Va can be reduced from 400 to 250 V. This technique appears amenable to providing fine variation and control of the laser output power. Possible applications in materials processing are pulse shaping and rapid power modulation (superpulsing).

Details of an experimental investigation of the gain and saturation intensity of a multichannel extended‐area discharge CO2 laser are presented. Measurements were made as a function of several discharge parameters. The gain coefficient was found to be similar in each of the individual discharge regions, having a maximum value of 0.70%/cm. Effects of gas pressure, gas mixture, and input power on gain and saturation parameters were studied. The saturation intensity varied as the square of the total gas pressure. The central interelectrode region of the device, which contained no visible discharge, exhibited a significant level of gain. The investigation reported herein provided important data for the design and optimization of optical extraction configurations.

A limiting feature in high-power laser technology which has surfaced in recent years is alignment instability induced by thermally generated distortions of the optical hardware and phase perturbations of the gain media under elevated power loading. In an effort to ameliorate these problems, a study was initiated to ascertain the feasibility of utilizing a feedback control system both to monitor and align the resonator optics of a multikilowatt laser; thereby actively preserving optimum mode quality. This papers summarizes the results of this project and outlines the basic approach used to construct a controller which accomplishes fully automatic alignment of both mirrors in an unstable resonator for a 20 kW CO2 machine. A mathematical model of the control system is presented along with a description of the principles of operation. Data are provided to document the major improvement in device performance achievable using this automatic alignment controller concept.

The valence region electronic structure of Ln(acac) 3 complexes (Ln = Nd, Tm, Pr; acac = acetylacetonate) is investigated using, principally, gas-phase ultraviolet photoelectron (PE) spectroscopy. Analysis of PE spectra focuses on the 7–12 eV region containing the first several ionization bands which likely contain metal f-ionizations and acac-based ionizations. These correspond to oxygen 2p-type orbitals and carbon 2p-type orbitals, which are equivalent to oxygen lone pairs and electrons from the pi-bond system of the ligand.

The output characteristics of a toric unstable resonator fitted to a multichannel stripline excitation system are presented. The resonator is shown to possess the usual advantages of a conventional unstable resonator plus the ability to modify the profile of the output beam by a simple change in the coupling aperture. Laser output parameters have been studied as a function of coupling fraction, magnification, and internal loss factors. Variations in the focal spot size as a function of the coupling aperture as well as resonator alignment sensitivity and polarization properties have been investigated.

The optical performance of a cw PIE CO(2) laser has been substantially improved through the adoption of a burst-mode gain switching technique. The approach has provided a doubling of the average beam power extractable from the device. With appropriate optimization, the process could possibly permit the attainment of pulsed energy extraction in the kilohertz range, and with average optical powers within the several tens of kilowatt category.

The design and operational features of a fluid-ballasted electrode structure for a high powered EDL CO(2) laser are described. This new device incorporates a crossed-tube geometry and as such is much simpler and inexpensive to fabricate than previous multielement or pin electrodes. Hot boundary layer formation at the electrode surfaces is minimized by a ducted flow-through feature also incorporated into the structure. This further assists in suppression of glow-to-arc transitions. The modular design used allows easy scaling to very large discharge volumes. A 40-liter cw CO(2) laser discharge system has recently been developed using this simplified crossed-tube fluid-ballasted electrode pair concept.

Photon absorption and photoionization spectra in a CO(2) laser mixture seeded with selected low ionization threshold additives are presented. Such data are used to determine total absorption and ionization cross sections for some gases and vapors of interest. The results identify tripropylamine as an interesting seedent material, as it exhibits a longer wavelength photoionization effect essentially independent of the primary host laser gases.

The authors examine whether greater futures-trading activity (volume and open interest) is associated with greater equity volatility. They partition each trading activity series into expected and unexpected components, and document that while equity volatility covaries positively with unexpected futures-trading volume, it is negatively related to forecastable futures-trading activity. Further, though futures-trading activity is systematically related to the futures contract life cycle, the authors find no evidence of a relation between the futures life cycle and spot equity volatility. These findings are consistent with theories predicting that active futures markets enhance the liquidity and depth of the equity markets. Copyright 1992 by American Finance Association.

The output characteristics of several large-area multichannel unstable resonators are presented. The conventional unstable resonator and a novel toric unstable resonator, in both confocal and nonconfocal configurations, have been studied. Output beam profiles, optical energy extraction, beam focusability, resonator alignment properties and polarization states of the various resonators have been analysed in depth.

A beam profile sensor for use in an automatic alignment and power stabilization system for a multikilowatt CO2 laser is described. An inexpensive pyroelectric array is used in conjunction with a diamond machined rotating wand, to provide on‐line samples of the laser beam. Interface circuits utilize the multiple outputs derived from the detector array for precise monitoring and control of the laser’s output radiation. Data from a 5‐kW CO2 laser are presented to characterize the response of this new beam profile sensor to major perturbations in the optical cavity and lasing gas chemistry. The device has demonstrated exceptional performance in the maintenance of both mode quality and optical power level.

The application of the magnetic discharge stabilization technique to high‐pressure laser discharges is investigated. Scaling laws are developed with the help of Monte Carlo simulations for the transverse discharge velocity and for the magnetic field strength that is necessary for discharge stability. The results that are obtained indicate that the required magnetic field strength scales as the pressure squared. Unless a cost‐effective means is found for implementing a very strong magnetic field into an electrode design, the magnetic discharge stabilization technique will be mainly relegated to low‐pressure systems.