In this paper, the dispersive nature of flexural waves is exploited to generate a shock response at an arbitrary location on a waveguide. The input waveform is an up-chirp whose instantaneous ...frequency is chosen to ensure synchronous arrival at an arbitrary focal point. An analytical expression is derived for the required chirp waveform as a function of bandwidth and focal point location given prior knowledge of the dispersion relation.
The principle is illustrated for an analytical model of a uniform beam. Simulated results show that it is possible, in theory, to achieve peak responses that are at least an order of magnitude larger than steady state response due to harmonic excitation. Further, the peak response increases with approximately the square root of distance from the point of excitation when damping is negligible. Velocity, acceleration, normal strain and shear stress exhibit qualitatively similar results which differ quantitatively owing to their different frequency responses with respect to the input.
A single degree-of-freedom model of an electrodynamic shaker is coupled to the analytical beam model in order to predict peak mechanical responses per peak input voltage of the chirp waveform. The coupled electromechanical model is then validated experimentally through both frequency response and transient measurements. The technique is potentially applicable to situations where a large and reasonably localised transient response is required on a beam or plate-like structure using minimal instrumentation.
A vibration isolator consisting of a vertical linear spring and two nonlinear pre-stressed oblique springs is considered in this paper. The system has both geometrical and physical nonlinearity. ...Firstly, a static analysis is carried out. The softening parameter leading to quasi-zero dynamic stiffness at the equilibrium position is obtained as a function of the initial geometry, pre-stress and the stiffness of the springs. The optimal combination of the system parameters is found that maximises the displacement from the equilibrium position when the prescribed stiffness is equal to that of the vertical spring alone. It also satisfies the condition that the dynamic stiffness only changes slightly in the neighbourhood of the static equilibrium position. For these values, a dynamical analysis of the isolator under asymmetric excitation is performed to quantify the undesirable effects of the nonlinearities. It includes considering the possibilities of the appearance of period-doubling bifurcation and its development into chaotic motion. For this purpose, approximate analytical methods and numerical simulations accompanied with qualitative methods including phase plane plots, Poincaré maps and Lyapunov exponents are used. Finally, the frequency at which the first period-doubling bifurcation appears is found and the effect of damping on this frequency determined.
A timely and provocative challenge to the foundations of our global order: why should national borders be unchangeable? The inviolability of national borders is an unquestioned pillar of the ...post-World War II international order. Fixed borders are believed to encourage stability, promote pluralism, and discourage nationalism and intolerance. But do they? What if fixed borders create more problems than they solve, and what if permitting borders to change would create more stability and produce more just societies? Legal scholar Timothy Waters examines this possibility, showing how we arrived at a system of rigidly bordered states and how the real danger to peace is not the desire of people to form new states but the capacity of existing states to resist that desire, even with violence. He proposes a practical, democratically legitimate alternative: a right of secession. With crises ongoing in the United Kingdom, Spain, Ukraine, Iraq, Syria, Sudan, and many other regions, this reassessment of the foundations of our international order is more relevant than ever.
Potato leafroll virus (PLRV) has been well managed by neonicotinoids since their widespread adoption in the United States, becoming virtually absent from seed and production fields in the Northwest. ...However, with increasing interest in discontinuing neonicotinoid usage, there is concern that PLRV could enjoy a resurgence in the absence of effective alternative chemistries. We tested the effects of afidopyropen, an insecticide with novel mode of action, on PLRV transmission and the feeding/probing behavior of its primary vector, the green peach aphid (Myzus persicae Sulzer). Afidopyropen foliar sprays decreased PLRV transmission by individual green peach aphids relative to water controls: PLRV acquisition from treated potato plants and subsequent transmission was reduced by 89%, and PLRV inoculation by viruliferous aphids to treated potato plants was reduced by 35%. Although electropenetrograph analyses following 4-h recordings of individual aphids on potato plants showed decreases in the total and mean duration of phloem feeding (E) on plants subject to an afidopyropen treatment relative to water, these only trended toward significance. Taken together, these results suggest treatment with afidopyropen can decrease PLRV transmission in potatoes, but that significant changes in feeding/probing might not occur quickly post-exposure. Overall, while the reductions in transmission were not as dramatic as have been observed following neonicotinoid treatments, afidopyropen may be a useful alternative and should be evaluated in field experiments.
Parker winds revisited: an extension to disc winds Waters, Timothy R.; Proga, Daniel
Monthly notices of the Royal Astronomical Society,
1 November 2012, 20121101, Letnik:
426, Številka:
3
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
A simple 1D dynamical model of thermally driven disc winds is proposed, based on the results of recent, 2.5D axisymmetric simulations. Our formulation of the disc wind problem is in the ...spirit of the original Parker and Bondi problems, namely we assume an elementary flow configuration consisting of an outflow following pre‐defined trajectories in the presence of a central gravitating point mass. Viscosity and heat conduction are neglected. We consider two different streamline geometries, both comprised of straight lines in the (x, z)‐plane: (i) streamlines that converge to a geometric point located at (x, z) = (0, −d) and (ii) streamlines that emerge at a constant inclination angle from the disc mid‐plane (the x‐axis, as we consider geometrically thin accretion discs). The former geometry is commonly used in kinematic models to compute synthetic spectra, while the latter, which exhibits self‐similarity, is likely unused for this purpose, although it easily can be with existing kinematic models. We make the case that it should be, i.e. geometry (ii) leads to transonic wind solutions with substantially different properties owing to its lack of streamline divergence. Both geometries can be used to complement recent efforts to estimate photoevaporative mass‐loss rates from protoplanetary discs. Pertinent to understanding our disc wind results, which are also applicable to X‐ray binaries and active galactic nuclei, is a focused discussion on lesser known properties of classic Parker wind solutions. We find that the parameter space corresponding to decelerating Parker wind solutions is made larger due to rotation and leads instead to disc wind solutions that always accelerate after the bulk velocity is slowed to a minimum value. Surprisingly, Keplerian rotation may allow for two different transonic wind solutions for the same physical conditions.
It is unclear if sickle cell trait (SCT) carrier status conveys an increased risk for poor outcomes following total hip arthroplasty (THA). The purpose of this study is to compare short-term clinical ...outcomes of THA for patients with SCT vs matched controls.
Patient records were queried from the PearlDiver database using International Classification of Diseases, Ninth and Tenth Revision and Current Procedural Terminology codes. Patients with SCT who underwent THA were matched 1:1 with controls across age, gender, Elixhauser Comorbidity Index, obesity, and US region. Thirty-day and 90-day rates of systemic complications and 1-year and 2-year rates of joint complications were compared with logistic regression.
In total, 1646 patients were assigned to each cohort. In the 30-day and 90-day postoperative periods, SCT carriers had a higher likelihood of cerebrovascular accident, anemia, acute renal failure, pneumonia, sepsis, deep vein thrombosis, pulmonary embolism, and respiratory failure (all P < .05). SCT carriers exhibited significantly higher risk of periprosthetic joint infection at both 1 (3.5% vs 2.1%; odds ratio OR 1.91, 95% confidence interval CI 1.22-2.99) and 2 years (3.7% vs 2.6%; OR 1.63, 95% CI 1.07-2.49) postoperatively. Prosthetic loosening was also significantly more likely for SCT carriers within 1 year (1.3% vs 0.3%; OR 4.49, 95% CI 1.75-13.86).
Patients with SCT exhibited significantly higher risk for systemic complications, periprosthetic joint infection, and prosthetic loosening after THA. Increased perioperative efforts should be made to prevent hypoxia, acidosis, and dehydration, as these states increase red blood cell sickling, which may reduce complication rates and improve outcomes in patients with SCT.
•Patients with SCT have increased systemic complications after THA.•Patients with SCT have higher rates of joint infection and loosening after THA.•Hydration and pH homeostasis may reduce complications post THA in this cohort.
Studies have demonstrated increased complication risk after total hip arthroplasty (THA) in patients who smoke cigarettes. It is unclear if smokeless tobacco use confers a similar impact. The purpose ...of this study was to (1) evaluate rates of postoperative complications after THA in smokeless tobacco users and people who smoke compared to matched controls, and (2) compare rates of postoperative complications in smokeless tobacco users versus patients who smoke.
A retrospective cohort study was conducted using a large national database. For patients who underwent primary THA, smokeless tobacco users (n = 950) and people who smoke (n = 21,585) were matched 1:4 with controls (n = 3,800 and 86,340, respectively), and smokeless tobacco users (n = 922) were matched 1:4 with people who smoke (n = 3,688). Joint complication rates within 2 years and medical complications within 90 days postoperatively were compared using multivariable logistic regressions.
Within 90 days of primary THA, smokeless tobacco users demonstrated significantly higher rates of wound disruption, pneumonia, deep vein thrombosis, acute kidney injury (AKI), cardiac arrest, transfusion, readmission and longer length of stay compared to tobacco naïve controls. Within 2 years, smokeless tobacco users demonstrated significantly higher rates of prosthetic joint dislocations and overall joint-related complications compared to tobacco naïve controls.
Smokeless tobacco use is associated with higher rates of medical- and joint-related complications following primary THA. Smokeless tobacco use may be under-diagnosed in patients undergoing elective THA. Surgeons may consider delineating between smoking and smokeless tobacco use during preoperative counseling.
This study highlights the persistent osteoporosis treatment gap following fragility fractures. Patients with multiple sclerosis sustained more primary hip fractures than controls and exhibited ...significantly higher rates of falls within three years post-fracture. However, multiple sclerosis (MS) patients were significantly more likely to be diagnosed with osteoporosis and treated with medications.
Introduction
The purpose of this study was to compare rates of osteoporosis management, falls, and secondary fractures following primary fragility fractures among patients with MS versus matched controls.
Materials and methods
A retrospective matched cohort study was conducted using the PearlDiver database. Patients aged ≥ 50 years with primary fragility fractures were identified (
n
= 120,368). Within this population, patients with MS were matched 1:10 with controls across age, sex, and US region. Rates of osteoporosis diagnoses and pharmacologic treatment, low-energy falls, and secondary fragility fractures were compared at three years post-fracture via logistic regression.
Results
A total of 1,232 patients with MS (mean age, 65.7 years) with primary fragility fractures were matched with 12,320 controls (mean age, 65.8 years). Primary hip fractures were significantly more common in the MS cohort (47.4% vs. 34.2%,
p
< 0.001). After the initial fracture, patients with MS were significantly more likely to receive a formal osteoporosis diagnosis (12.9% vs. 9.7%;
OR
1.35; 95%
CI
, 1.13–1.61) and osteoporosis pharmacotherapy (14.4% vs. 11.9%;
OR
1.24; 95%
CI
, 1.04–1.46). The MS cohort also exhibited significantly higher rates of falls (27.8% vs 22.7%;
OR
1.15; 95%
CI
, 1.01–1.32). Rates of secondary fractures were comparable (6.3% vs. 5.0%;
OR
1.10; 95%
CI
, 0.85–1.40).
Conclusion
Primary hip fragility fractures were significantly more common in patients with MS compared to matched controls. Following an initial fracture, patients with MS exhibited a significantly higher rate of falls but were more likely to be diagnosed with osteoporosis and treated with medications.
Studies have demonstrated increased complication risk after total knee arthroplasty (TKA) in patients who smoke cigarettes, but it is unclear if smokeless tobacco use confers a similar impact. The ...purpose of this study was to (1) evaluate rates of postoperative complications after TKA in smokeless tobacco users and smokers as compared to matched controls, and (2) compare rates of postoperative complications in smokeless tobacco users versus smokers to determine if one is associated with significantly higher rates of postoperative complications.
A retrospective cohort study was conducted using a national database. For patients who underwent primary TKA, smokeless tobacco users (n = 1,535) and smokers (n = 28,953) were matched at a 1:4 with controls (n = 6,140 and 115,812, respectively), and smokeless tobacco users (n = 1,481) were matched at a 1:4 with smokers (n = 5,924). Rates of joint complications within 2 years and medical complications within 90 days postoperatively were compared using multivariable logistic regressions.
After primary TKA, compared to controls, smokeless tobacco users demonstrated significantly higher rates of aseptic loosening/mechanical failure within 2 years, longer lengths of stay, and higher rates of urinary tract infection, pneumonia, deep vein thrombosis, and acute kidney injury within 90 days. Compared to smokers, smokeless tobacco users demonstrated significantly lower rates of aseptic revision and lower rates of wound disruption.
Smokeless tobacco use is associated with higher rates of both medical and joint complications following primary TKA. However, smoking is associated with higher risk for complications than smokeless tobacco use.
Level III.
To use an expected-value decision analysis to determine the optimal treatment decision between repair or a biceps tenodesis (BT) for an isolated type II Superior Labral Anterior Posterior (SLAP) ...injury.
An expected-value decision analysis with sensitivity analysis was performed to systematically quantify the clinical decision. To determine outcome probabilities, a decision tree was constructed (repair vs BT) and a meta-analysis was conducted. To determine outcome utilities, we evaluated 70 patients with a chief complaint of shoulder pain with regard to age, sex, Shoulder Activity Level (SAL) and visual analog scale regarding potential outcome preferences. Statistical fold back analysis calculated optimal treatment. One-way sensitivity analysis determined the effect of changing the reinjury rate on the expected value of a biceps tenodesis.
The overall expected value for biceps tenodesis was 8.66 versus 7.19 for SLAP repair. One-way sensitivity demonstrated that biceps tenodesis was the superior choice if reinjury rates are expected to be less than 28%. Meta-analysis of 23 studies and 908 patients revealed the probability of a well outcome was significantly greater for BT (87.8%; 95% CI 74.9-94.6%, I2=0.0%) than SLAP repair (62.9%; 95% CI 55.9-69.3%, I2=65.9%; p=0.0023). Reinjury with BT was 1.5% (95% CI 0.05% to 33.8%, I2=0.0%) and repair 6.4% (95% CI 4.2%-9.6%, I2=24%) which was not statistically significantly different (p=0.411). 50 participants mean age=25.4 (SD 8.9), male = 76%; overhead athletes = 50% met inclusion criteria. Forty-six percent of participants had a SAL score of ‘high’.
Decision analysis demonstrated that biceps tenodesis is preferred over repair for an isolated type II SLAP tear based on greater expected value of BT versus repair. Meta-analysis demonstrated more frequent favorable outcomes with BT. Surgeons can use this information to tailor discussion with patients..
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