The effectiveness of vane-aileron excitation in the experimental determination of flutter speed by parameter identification

The effectiveness of aerodynamic excitation is evaluated analytically in conjunction with the experimental determination of flutter dynamic pressure by parameter identification. Existing control surfaces were used, with an additional vane located at the wingtip. The equations leading to the identification of the equations of motion were reformulated to accommodate excitation forces of aerodynamic origin. The aerodynamic coefficients of the excitation forces do not need to be known since they are determined by the identification procedure. The 12 degree-of-freedom numerical example treated in this work revealed the best wingtip vane locations, and demonstrated the effectiveness of the aileron-vane excitation system. Results from simulated data gathered at much lower dynamic pressures (approximately half the value of flutter dynamic pressure) predicted flutter dynamic pressures with 2-percent errors

Design of control laws for flutter suppression based on the aerodynamic energy concept and comparisons with other design methods

The aerodynamic energy method is used to synthesize control laws for NASA's drone for aerodynamic and structural testing-aerodynamic research wing 1 (DAST-ARW1) mathematical model. The performance of these control laws in terms of closed-loop flutter dynamic pressure, control surface activity, and robustness is compared with other control laws that relate to the same model. A control law synthesis technique that makes use of the return difference singular values is developed. It is based on the aerodynamic energy approach and is shown to yield results that are superior to those results given in the literature and are based on optimal control theory. Nyquist plots are presented, together with a short discussion regarding the relative merits of the minimum singular value as a measure of robustness as compared with the more traditional measure involving phase and gain margins

Stock Option Expense, Forward-Looking Information, and Implied Volatilities of Traded Options

Prior research generally finds that firms underreport option expense by managing assumptions underlying option valuation (e.g. they shorten the expected option lives), but it fails to document management of a key assumption, the one concerning expected stock-price volatility. Using a new methodology, we address two questions: (1) To what extent do companies follow the guidance in FAS 123 and use forward looking information in addition to the readily available historical volatility in estimating expected volatility? (2) What determines the cross-sectional variation in the reliance on forward looking information? We find that firms use both historical and forward-looking information in deriving expected volatility. We also find, however, that the reliance on forward-looking information is limited to situations where this reliance results in reduced expected volatility and thus smaller option expense. We interpret this finding as managers opportunistically use the discretion in estimating expected volatility afforded by FAS 123. In support of this interpretation, we also find that managerial incentives play a key role in this opportunism

Stock Option Expense, Forward-Looking Information, and Implied Volatilities of Traded Options

Prior research generally finds that firms underreport option expense by managing assumptions underlying option valuation (e.g. they shorten the expected option lives), but it fails to document management of a key assumption, the one concerning expected stock-price volatility. Using a new methodology, we address two questions: (1) To what extent do companies follow the guidance in FAS 123 and use forward looking information in addition to the readily available historical volatility in estimating expected volatility? (2) What determines the cross-sectional variation in the reliance on forward looking information? We find that firms use both historical and forward-looking information in deriving expected volatility. We also find, however, that the reliance on forward-looking information is limited to situations where this reliance results in reduced expected volatility and thus smaller option expense. We interpret this finding as managers opportunistically use the discretion in estimating expected volatility afforded by FAS 123. In support of this interpretation, we also find that managerial incentives play a key role in this opportunism

Partial Calcanectomy for Heel Ulcers Revisited – a Possible Solution to a Difficult Problem

Category: Diabetes Introduction/Purpose: Diabetic heel ulcers are a major problem, often leading to amputations. Partial or total calcanectomy has been described as a possible salvage procedure, by allowing soft tissue coverage after debridement of necrotic and infected tissue, and possibly allowing walking. We report on our experience with this technique which is not commonly used Methods: Fourteen patients, who presented with diabetic heel ulcers between 2010-15, and who were BKA candidates, underwent debridement and partial calcanectomy. Average age was 67.8 ±12.7 years, M:F ratio was 6:1 Extent of procedures, need for additional procedures and complications were noted. Outcome assessment included wound closure and walking status. No patients were lost to follow up. Results: Nine patients underwent partial calcanectomy as the initial procedure while others underwent prior debridement. Calcanectomies were subtotal (1), wedge (5) or partial (8). Primary closure was mostly achieved (11), the remainder requiring local skin graft (2) or myocutaneous flap (1). Ten patients underwent re-vascularization prior to calcanectomy, either angiographic (8) or bypass (2). Most calcanectomies (9/14) healed successfully, while five subsequently required amputations. Most failures were noticed within 24 days, with similar prevalence in wedge and partial calcanectomies. One patient had wound complications requiring BKA. At one year, the nine patients had full wound closure and could bear weight. Five patients regained full ambulatory status wearing specially modified shoes with custom fillers. Conclusion: Partial calcanectomy is a little-known procedure, that is a viable alternative to BKA. We present our positive experience with this procedure, which in a majority of cases not only prevented BKA, but also allowed weight bearing. Poor vascular supply is not necessarily a contraindication, as re-vascularization prior to calcanectomy is a viable option

IS SPINAL METASTASIS PALLIATIVE SURGERY WARRANTED?

Background: There is no consensus on the preferred treatment for spinal metastasis patients. Aims: We evaluated 63 patients undergoing surgery for spinal metastasis at our Institute, in an attempt to revise the indications for these surgical procedures. Methods: The study population was divided into two groups: patients with cord compression and those with intractable pain only. Patients' Frankel score, ambulatory and incontinence status were examined before surgery, at discharge and at last follow up and their cumulative survival was analyzed . Results: Patients with cord compression showed no significant differences in the Frankel score at the different points in time. Cord compression patients' continence status deteriorated at the last visit. Median survival of the cord compression and non-cord compression groups was 201 and 402 days, respectively (p=0.317). Conclusions: Since the benefits of surgery are weighed against survival, overall survival is gloomy in both groups of patients, by definition, and the functional level of most patients has deteriorated at last follow up, surgeons should probably refrain from aggressive treatment of these patients. A revision of the indications for spinal metastasis surgery should be undertaken