Neutral Return Research Articles

Hybrid bipolar VSC-DRU HVdc connection for offshore wind farms

This paper presents a hybrid bipolar high voltage direct current (HVdc) link for offshore wind farms (OWFs) connection. Voltage source converter (VSC) technology is used in one of the offshore poles, using a diode rectifier unit (DRU) in the other one. Therefore, economic and power-loss advantages of the DRU over the VSC are leveraged by changing one of the HVdc poles conventional technology. In the proposed control strategy, VSC reactive power is used to control OWF ac grid frequency, allowing the DRU commutation and active power transfer. VSC active power is used for OWF ac grid start-up and hybrid bipolar HVdc link power flow control. OWF ac grid voltage magnitude is controlled while the DRU pole is blocked, and it is automatically accommodated to the required value when the DRU is conducting. Moreover, VSC is also used as an active filter for the main DRU current harmonic components, thus removing the huge passive ac filters from the offshore platform. Poles balanced and unbalanced power flow control strategies are proposed for the hybrid bipolar HVdc, considering both bipolar with neutral return and rigid bipolar configurations. Simulation results validate the proposal which aims reducing cost and size of the OWF HVdc connection.

OPTION SURFACE STATISTICS WITH APPLICATIONS

At each maturity a discrete return distribution is inferred from option prices. Option pricing models imply a comparable theoretical distribution. As both the transformed data and the option pricing model deliver points on a simplex, the data is statistically modeled by a Dirichlet distribution with expected values given by the option pricing model. The resulting setup allows for maximum likelihood estimation of option pricing model parameters with standard errors that enable the testing of hypotheses. Hypothesis testing is then illustrated by testing for the consistency of risk neutral return distributions being those of a Brownian motion with drift time changed by a subordinator. Models mixing processes of independent increments with processes related to solutions of Ornstein–Uhlenbeck (OU) equations are also tested for the presence of the OU component. Solutions to OU equations may be viewed as processes of perpetual motion responding continuously to their past movements. The tests support the rejection of Brownian subordination and the presence of a perpetual motion component.

Forensic Engineering Analysis of a Swimming Pool Electric Shock Injury

This case involves a minor who received an electric shock while swimming in a membership swimming pool. Her family sued the pool association, its president, the electric utility, and others. At some time, tree trimmers had accidentally severed the service drop’s neutral return wire. The electric utility made a temporary splice repair, but did not permanently replace the wire until several years later (after the incident). The forensic engineer (FE) was retained by counsel for the pool and its president to opine on electrical aspects of the plaintiff’s complaints. The FE inspected the pool premises, reviewed documents, and examined the spliced service wires in storage. The FE opined that the pool association and its president were not negligent or careless — and that the electric utility failed its responsibility to maintain the service drop. This report discusses three-phase electric power, current flow, and how a severed neutral can cause a shock.

Option Surface Econometrics with Applications

At each maturity a discrete return distribution is inferred from option prices. Option pricing models imply a comparable theoretical distribution. As both the transformed data and the option pricing model deliver points on a simplex, the data is statistically modeled by a Dirichlet distribution with expected values given by the option pricing model. The resulting setup allows for maximum likelihood estimation of option pricing model parameters with standard errors enabling the test of hypotheses. Hypothesis testing is illustrated by testing for risk neutral return distributions being consistent with Brownian motion with drift time changed by a subordinator. Models mixing processes of independent increments with processes related to solution of Ornstein Uhlenbeck (OU) equations are tested for the presence of the OU component. OU equations are a form of perpetual motion processes continuously responding to their past changes. The tests support the rejection of Brownian subordination and the presence of a perpetual motion component.

Natural Interest Rate and Money Interest Rates

Abstract The long lasting period of declining interest rates raises the question, whether the latter result from a savings glut, from a money glut, or from both. Moreover, it renewed the old question how the natural interest rate should be sensibly defined, and if it could ever fall below the growth rate, thereby causing dynamic inefficiency. The present article contributes to this debate on a pure theoretical base, leaving the empirical issue for other research. In particular, I briefly discuss Böhm-Bawerk’s three causes for the existence of an interest rate in a private barter economy. I argue that the natural interest rate remains a meaningful concept even in an economy with both a public sector and money. From a welfare economic view, it is also preferable above the so-called golden rule, provided the interest rate does not fall below the growth rate. Although the natural interest rate could well get negative by excess saving in principle, this is normally prevented when durable goods like land or precious metals are available for storing private wealth. On the other hand, issuing credit money tends to push the interest rate below its natural level, even in the long run. In order to prevent this, one could either replace it by neutral helicopter money or return to a gold currency.

The Return on Investment of Orthopaedic Fellowship Training: A Ten-year Update.

Over 90% of graduating orthopaedic residents now pursue fellowship training, and only 15% of practicing orthopaedic surgeons now characterize themselves as generalists. Fellowship training has significant financial effects due to both opportunity cost of that year of training and changes in compensation throughout one's career. The purpose of this study was to estimate the financial return on investment by pursuing additional training in an orthopaedic fellowship versus general practice. Using described techniques of financial analysis, net present value (NPV), internal rate of return (IRR), and break-even point were estimated over the average working career length of an orthopaedic surgeon. Compensation data were drawn from the American Medical Group Association physician compensation surveys. Seven fellowships were studied and referenced to a career in general orthopaedic practice. Fellowship training in spine surgery yields the highest return on investment with a break-even point of 5 years. Adult reconstruction has a positive NPV and IRR, but when corrected for number of hours worked per week offers no productivity advantage to general practice. Sports medicine and trauma offer neutral returns, but when corrected for work hours, NPV and IRR both become negative. Hand, pediatrics, and foot and ankle never break even following the loss of compensation realized during fellowship year. The recent trend across all medical specialties has been for increased fellowship training and subspecialization. There are numerous reasons to pursue fellowship training, both personal and financial. This study presents an updated estimate of the financial impact of fellowship training in orthopaedics. This analysis demonstrates that selecting different fellowships can generate positive, negative, or neutral financial returns. This study has the potential to influence residents' decisions to pursue general practice versus fellowship training and identifies economic drivers, which may lead to preferential pursuit of certain subspecialties.

Closingbell Crowdsourced Stock Ratings

ClosingBell is an app-based collaborative stock trading platform which allows its users to connect their online brokerage accounts and share their trades and portfolios with one another. Users, who are retail traders, can also share their trade ideas, or ratings, with the ClosingBell community. The ClosingBell crowdsourced stock ratings dataset includes all such Buy and Sell ratings issued by the community’s members since 2014, currently over 47,000 ratings from 2,800 contributors. In this paper we examine the predictive power of the ClosingBell ratings, and find that the ratings are predictive of stock prices over a one to twenty trading day period. The returns of portfolios built using the ratings exhibit dollar neutral returns of 12% with a Sharpe ratio of 1.0. These returns are robust to trading costs and are not explained by common risk factors. The ClosingBell data represents a unique and powerful source of crowdsourced alpha which can improve systematic sentiment strategies.

Insider trading, stock return volatility, and the option market's pricing of the information content of insider trading

Abstract We find strong evidence that net insider selling is positively associated with future stock return volatility, consistent with insider selling increasing outside investors’ uncertainty. The positive effect of net insider selling is significantly stronger when the volatility is measured around the earnings announcement. Apparently, option prices do not fully reflect the information content of insider trading for future volatility. More specifically, we find no evidence that option traders adjust the implied volatility for the insider trading effect in a timely manner. Consequently, net insider selling is significantly associated with future option straddle returns and delta neutral returns.

Too Good to be True? An Analysis of the Options Market's Reactions to Earnings Releases

Using option implied risk neutral return distributions before and after earnings announcements, we study the option market's reaction to extreme events over earnings announcements. While earnings announcements generally reduce short-term uncertainty about the stock price, very good news does not reduce uncertainty and slightly bad news actually increases uncertainty. We also find that left tail probabilities decrease over earnings releases while right tail probabilities increase. We interpret these findings as evidence of maintained investor expectations that very good news is generally not released during earnings announcements, combined with skepticism in the form of lingering uncertainty at the release of such very good news. [ABSTRACT FROM AUTHOR]

Monitoring and remediation of on-farm and off-farm ground current measured as step potential on a Wisconsin dairy farm: A case study

ABSTRACTGround current commonly referred to as “stray voltage” has been an issue on dairy farms since electricity was first brought to rural America. Equipment that generates high-frequency voltage transients on electrical wires combined with a multigrounded (electrical distribution) system and inadequate neutral returns all contribute to ground current. Despite decades of problems, we are no closer to resolving this issue, in part, due to three misconceptions that are addressed in this study. Misconception 1. The current standard of 1 V at cow contact is adequate to protect dairy cows; Misconception 2. Frequencies higher than 60 Hz do not need to be considered; and Misconception 3. All sources of ground current originate on the farm that has a ground current problem. This case study of a Wisconsin dairy farm documents, 1. how to establish permanent monitoring of ground current (step potential) on a dairy farm; 2. how to determine and remediate both on-farm and off-farm sources contributing to step potential; 3. which step-potential metrics relate to cow comfort and milk production; and 4. how these metrics relate to established standards. On-farm sources include lighting, variable speed frequency drives on motors, radio frequency identification system and off-farm sources are due to a poor primary neutral return on the utility side of the distribution system. A step-potential threshold of 1 V root mean square (RMS) at 60 Hz is inadequate to protect dairy cows as decreases of a few mV peak–peak at higher frequencies increases milk production, reduces milking time and improves cow comfort.

Spectra of accelerated particles at supernova shocks in the presence of neutral hydrogen: the case of Tycho

The presence of neutral hydrogen in the shock proximity changes the structure of the shock and affects the spectra of particles accelerated through the first-order Fermi mechanism. This phenomenon has profound implications for the interpretation of the multifrequency spectra of radiation from supernova remnants. Neutrals that undergo charge exchange with hot ions downstream of the shock may result in fast neutrals moving towards the upstream gas, where they can suffer additional charge exchange or ionisation reactions, thereby depositing energy and momentum upstream. Here we discuss the implications of this neutral return flux, which was already predicted in our previous work on neutral mediated supernova shocks, and show how the spectra of accelerated particles turn out to be appreciably steeper than $p^{-4}$, thereby affecting the gamma ray spectra from supernova remnants in general and from Tycho specifically. The theory that describes non-linear diffusive shock acceleration in the presence of neutral hydrogen has been developed in recent years. Here we use a semi-analytical theory developed in previous work and specialise our predictions to the case of the Tycho supernova shock, where there is evidence that the spectrum of the accelerated cosmic rays is steeper than expected from the traditional theory of diffusive shock acceleration. We show that, if the fraction of neutral hydrogen in the vicinity of the Tycho supernova shock is, as suggested by observations, ~70-90, then spectra of accelerated protons steeper than $p^{-4}$ may be a natural consequence of charge exchange reactions and the associated neutral return flux. The spectral shape is affected by this phenomenon for particles with energies below ~100-1000 GeV, for which the diffusion length is less than or at most comparable to the pathlength of charge exchange and ionisation upstream of the shock.

In-depth plasma-wave heating of dense plasma irradiated by short laser pulses.

We investigate the mechanism by which relativistic electron bunches created at the surface of a target irradiated by a very short and intense laser pulse transfer energy to the deeper parts of the target. In existing theories, the dominant heating mechanism is that of resistive heating by the neutralizing return current. In addition to this, we find that large amplitude plasma waves are induced in the plasma in the wake of relativistic electron bunches. The subsequent collisional damping of these waves represents a source of heating that can exceed the resistive heating rate. As a result, solid targets heat significantly faster than has been previously considered. A new hybrid model, capable of reproducing these results, is described.

Is Subspecialty Fellowship Training Emerging as a Necessary Component of Contemporary Orthopaedic Surgery Education?

The current minimum training standard for orthopaedic surgeons in the United States consists of a 5-year orthopaedic surgery residency program with the option to pursue subsequent fellowship training.1 Traditionally, orthopaedic residency training was intended to expose residents to all aspects of orthopaedic surgery and prepare them for general orthopaedic practice.1,2 The demand for increasing subspecialization, more duty hour restrictions, and greater supervision requirements have rapidly changed the clinical experience of orthopaedic surgery trainees. As training requirements and expectations for orthopaedic surgical graduates continue to expand and the body of knowledge and technical applications in orthopaedic surgery continue to grow, it has become more apparent that our traditional 5-year residency pathway may be increasingly insufficient for preparing trainees for the future world of independent orthopaedic surgical practice. Subspecialty fellowship training, therefore, may be evolving as an educational necessity to help trainees meet the demands of society's evolving definition of orthopaedic competence rather than an educational option. Compared to several decades ago when a minority of orthopaedic surgery trainees pursued additional fellowship training,3 approximately 90% of the current class of orthopaedic graduates plans to complete at least 1 fellowship after completing residency.4–,6 There also seems to be a new trend toward pursuing more than 1 fellowship.6 All of these transitions have coincidentally appeared with the recent changes in residency training regulations and societal expectations. It is possible that this is a matter of simple math: shorter periods of clinical exposure (less input) cannot possibly result in equal experience upon graduation (same output). Since the baseline input (residency training) cannot be overhauled, additional input (fellowship training) is sought to reach the same end point.

Momentum and reversion in risk neutral martingale probabilities

A time homogeneous, purely discontinuous, parsimonous Markov martingale model is proposed for the risk neutral dynamics of equity forward prices. Transition probabilities are in the variance gamma class with spot dependent parameters. Markov chain approximations give access to option prices. The model is estimated on option prices across strike and maturity for five days at a time. Properties of the estimated processes are described via an analysis of return quantiles, momentum functions that measure the response of tail probabilities to such moves. Momentum and reversion are also addressed via the construction of reverse conditional expectations. Term structures for the moments of marginal distributions support a decay in skewness and excess kurtosis with maturity at rates slower than those implied by Lévy processes. Out of sample performance is additionally reported. It is observed that risk neutral dynamics by and large reflect the presence of momentum in numerous probabilities. However, there is some reversion in the upper quantiles of risk neutral return distributions.

COLLISIONLESS SHOCKS IN A PARTIALLY IONIZED MEDIUM. III. EFFICIENT COSMIC RAY ACCELERATION

In this paper we present the first formulation of the theory of non-linear particle acceleration in collisionless shocks in the presence of neutral hydrogen in the acceleration region. The dynamical reaction of the accelerated particles, the magnetic field amplification and the magnetic dynamical effects on the shock are also included. The main new aspect consists however in accounting for charge exchange and ionization of neutral hydrogen, which profoundly change the structure of the shock, as discussed in our previous work. This important dynamical effect of neutrals is mainly associated to the so-called neutral return flux, namely the return of hot neutrals from the downstream region to the upstream, where they deposit energy and momentum through charge exchange and ionization. We also present the self-consistent calculation of Balmer line emission from the shock region and discuss how to use measurements of the anomalous width of the different components of the Balmer line to infer the cosmic ray acceleration efficiency in supernova remnants showing Balmer emission: the broad Balmer line, which is due to charge exchange of hydrogen atoms with hot ions downstream of the shock, is shown to become narrower as a result of the energy drainage into cosmic rays, while the narrow Balmer line, due to charge exchange in the cosmic-ray--induced precursor, is shown to become broader. In addition to these two well-known components, the neutral return flux leads to the formation of a third component with intermediate width: this too contains information on ongoing processes at the shock.

Momentum and Reversion in Risk Neutral Martingale Probabilities

A time homogeneous, purely discontinuous, parsimonous Markov martingale model is proposed for the risk neutral dynamics of equity forward prices. Transition probabilities are in the variance gamma class with spot dependent parameters. Markov chain approximations give access to option prices. The model is estimated on option prices across strike and maturity for five days at a time. Properties of the estimated processes are described via an analysis of return quantiles, momentum functions that measure the response of tail probabilities to such moves. Momentum and reversion are also addressed via the construction of reverse conditional expectations. Term structures for the moments of marginal distributions support a decay in skewenss and excess kurtosis with maturity at rates slower than those implied by Levy processes. Out of sample performance is additionally reported. It is observed that risk neutral dynamics by and large reflect the presence of momentum in numerous probabilities. However, there is some reversion in the upper quantiles of risk neutral return distributions.

COLLISIONLESS SHOCKS IN A PARTIALLY IONIZED MEDIUM. I. NEUTRAL RETURN FLUX AND ITS EFFECTS ON ACCELERATION OF TEST PARTICLES

A collisionless shock may be strongly modified by the presence of neutral atoms through the processes of charge exchange between ions and neutrals and ionization of the latter. These two processes lead to exchange of energy and momentum between charged and neutral particles both upstream and downstream of the shock. In particular, neutrals that suffer a charge exchange downstream with shock-heated ions generate high velocity neutrals that have a finite probability of returning upstream. These neutrals might then deposit heat in the upstream plasma through ionization and charge exchange, thereby reducing the fluid Mach number. A consequence of this phenomenon, that we refer to as the "neutral return flux", is a reduction of the shock compression factor and the formation of a shock precursor upstream. The scale length of the precursor is determined by the ionization and charge exchange interaction lengths of fast neutrals moving towards upstream infinity. In the case of a shock propagating in the interstellar medium, the effects of ion-neutral interactions are especially important for shock velocities < 3000 km/s. Such propagation velocities are common among shocks associated with supernova remnants, the primary candidate sources for the acceleration of Galactic cosmic rays. We then investigate the effects of the return flux of neutrals on the spectrum of test-particles accelerated at the shock. We find that, for shocks slower than ~3000 km/s, the particle energy spectrum steepens appreciably with respect to the naive expectation for a strong shock, namely E^-2.

Too Good to Be True? An Analysis of the Options Market's Reactions to Earnings Releases

Using option implied risk neutral return distributions before and after earnings announcements, we study the option market's reaction to extreme events over earnings announcements. While earnings announcements generally reduce short term uncertainty about the stock price, very good news does not reduce uncertainty and slightly bad news actually increases uncertainty. Cross-sectional tests of realized volatility reductions are largely in line with option implied findings, except for cases where very good news is released, which suggests an irrational level of perceived uncertainty in options markets following very good news. We also find that left tail probabilities decrease over earnings releases while right tail probabilities increase. We interpret these findings as evidence of maintained investor expectations that very good news is generally not released during earnings announcements combined with unwarranted skepticism at the release of such news.

When There is No Place to Hide - Correlation Risk and the Cross-Section of Hedge Fund Returns

Using a novel dataset on correlation swaps, we study the relation between correlation risk, hedge fund characteristics and their risk-return profile. We find that hedge funds' ability to create market neutral returns is often associated with a significant exposure to correlation risk, which helps to explain the large abnormal returns found in previous models. We also estimate a significant negative market price of correlation risk, which accounts for the cross-section of hedge fund excess returns. Finally, we detect a pronounced nonlinear relation between correlation risk exposure and the tail risk of hedge fund returns.

The Influence of Mouth Opening on Oropharyngeal Leak Pressure, Intracuff Pressure, and Cuff Position With the Laryngeal Mask Airway

The aim of this study was to investigate the influence of mouth opening on oropharyngeal leak pressure, intracuff pressure, and cuff position of the laryngeal mask airway (LMA). Fifteen patients who were scheduled for elective oral surgery were recruited into this study. A single, experienced LMA user inserted the LMA according to the manufacturer's recommended technique. Oropharyngeal leak pressure, intracuff pressure, and fiberoptic assessment of the LMA position were documented under 3 mouth conditions: neutral position (1.4-cm distance between upper and lower incisors), mouth open (5- to 6-cm distance between upper and lower incisors), and return to the neutral position. Any ventilation difficulties under the 3 mouth conditions were recorded. Oropharyngeal leak pressure with the mouth open was higher than in the neutral position (P < .001). Compared with the neutral position, intracuff pressure was also higher with the mouth open (P < .001). Both measurement values returned to control levels when the neutral position was once again assumed. The LMA position observed by fiberoptic bronchoscopy was unchanged by mouth opening and was similar in the 3 mouth conditions (P = .998). Although ventilatory difficulties occurred after mouth opening in 8 of 15 patients (P < .001), it did not occur when the neutral position was reassumed. This study showed that mouth opening led to substantial increases in oropharyngeal leak pressure and intracuff pressure of the LMA, warranting caution because gastric insufflation, sore throat, and ventilation difficulties may occur.