Characteristics of coexisting attractors and ghost orbiting in an optomechanical microresonator.

We explore the nonlinear interactions of an optomechanical microresonator driven by two external optical signals. Optical whispering-gallery waves are coupled to acoustic surface waves of a fused silica medium in the equatorial plane of a generic microresonator. The system exhibits coexisting attractors whose behaviors include limit cycles, steady states, tori, quasi-chaos, and fully developed chaos with ghost orbits of a known attractor. Bifurcation diagrams demonstrate the existence of self-similarity, periodic windows, and coexisting attractors and show high-density lines within chaos that suggests a potential ghost orbit. In addition, the Lyapunov spectral components as a function of control parameter illuminate the dynamic nature of attractors and periodic windows with symmetric and asymmetric formations, their domains of existence, their bifurcations, and other nonlinear effects. We show that the power-shift method can access accurately and efficiently attractors in the optomechanical system as it does in other nonlinear systems. To test whether the ghost orbit is the link between two attractors interrupted by chaos, we examine the elements of the bifurcation diagrams as a function of control parameter. We also use detuning as a second control parameter to avoid the chaotic region and clarify that the two attractors are one.

Predicting attractor characteristics using Lyapunov exponents in a laser with injected signal.

Coexisting attractors are studied in a single-mode coherent model of a laser with an injected signal. We report that every attractor has a unique Lyapunov exponent (LE) pattern that is choreographed by the subtle variations in the attractor's dynamics and circumscribed by a common Lyapunov spectral pattern that begins and ends with two-zero LEs. Lyapunov spectra form symmetric-like and asymmetric bubbles; the former foreshadows an attractor's proximity to the cusp of an eminent change in dynamics and the latter indicates the presence of a bifurcation. We show that the peak values of the asymmetric bubbles are always associated with two-zero LEs; in fact, they are allied inseparably in forecasting period-doubling episodes. The two-zero LEs' predictor of torus dynamics is refined to include the convergence of three LEs to a triplet of zeros as a precursor to the two-zero spectra. We report that the long-standing two-zero LEs' signature is a necessary but not sufficient condition for predicting attractors and their dynamic conditions. The evolution of the attractor volume as a function of the injected signal is compared to the spectral formation of the attractor; we report slope changes and points of inflections in the volume trajectory where spectral changes indicate dynamic changes. Attractor viability is tested preliminarily by including random low-level noise in the frequency of the injected signal.

Isolated revision of the polyethylene component at revision total knee arthroplasty has excellent survivorship at ten years.

AIMS: The aim of this study was to establish the results of isolated exchange of the tibial polyethylene insert in revision total knee arthroplasty (RTKA) in patients with well-fixed femoral or tibial components. We report on a series of RTKAs where only the polyethylene was replaced, and the patients were followed for a mean of 13.2 years (10.0 to 19.1). PATIENTS AND METHODS: Our study group consisted of 64 non-infected, grossly stable TKA patients revised over an eight-year period (1998 to 2006). The mean age of the patients at time of revision was 72.2 years (48 to 88). There were 36 females (56%) and 28 males (44%) in the cohort. All patients had received the same cemented, cruciate-retaining patella resurfaced primary TKA. All subsequently underwent an isolated polyethylene insert exchange. The mean time from the primary TKA to RTKA was 9.1 years (2.2 to 16.1). RESULTS: At final follow-up, 13 patients had died, leaving 51 patients for study. Only seven of these patients had required re-operation. Knee Society scores (KSS) prior to RTKA were a mean of 78.4 (24 to 100). By six weeks post-revision, the mean total KSS was 93.5 (38 to 100) and at final follow-up, they had a mean of 91.6 (36 to 100). CONCLUSION: In appropriate circumstances, where the femoral and tibial components are satisfactorily aligned and well fixed, and where the soft tissues can be balanced, a polyethylene exchange alone can provide a durable solution for these RTKA patients. Cite this article: Bone Joint J 2019;101-B(7 Supple C):104-107.

Impact of UK National Guidelines based on FRAX®--comparison with current clinical practice.

OBJECTIVE: To assess whether clinician-determined treatment intervention thresholds are in line with the assessment of fracture risk provided by FRAX® and treatment recommendations provided by UK guidelines produced by the National Osteoporosis Guidelines Group (NOGG). DESIGN, PATIENTS AND MEASUREMENTS: This was a retrospective cohort analysis of 288 patients consecutively referred for dual-energy X-ray absorptiometry (DXA) scanning from primary care immediately prior to the introduction of the FRAX® algorithm. In addition to DXA assessment, patients completed a clinical risk factor questionnaire which included risk factors used in the FRAX® algorithm. Initial risk assessment and treatment decisions were performed after DXA. FRAX® was used, retrospectively, with femoral neck T-score, to estimate fracture risk which was applied to NOGG to generate guidance on treatment intervention. Clinician- and NOGG-determined outcomes were audited for concordance. RESULTS: There was concordance between clinician and NOGG treatment decisions in 215 (74.6%) subjects. Discordance was observed in 73 (25.3%) subjects. In the discordant group, seven subjects were given lifestyle advice when NOGG recommended treatment, 42 given treatment when NOGG recommended lifestyle advice only, and 24 were referred to a metabolic bone clinic for further evaluation. The reasons for treatment differences in subjects recommended treatment by clinician but not NOGG were largely (90.2%) attributed to the use of lumbar spine bone mineral density (BMD). CONCLUSIONS: There is high concordance between clinician-determined and FRAX®-NOGG intervention. The absence of spine BMD from FRAX® is the primary source of discrepancy. This study provides some assurance of the validity of the treatment thresholds generated from FRAX®-NOGG in 'real-world' usage.

Dispersion of interface waves in sediments with power-law shear speed profiles. I. Exact and approximate analytical results.

In the upper tens of meters of ocean bottom, unconsolidated marine sediments consisting of clay, silt, or fine sand with high porosity are "almost incompressible" in the sense that the shear wave velocity is much smaller than the compressional wave velocity. The shear velocity has very large gradients close to the ocean floor leading to strong coupling of compressional and shear waves in such "soft" sediments. The weak compressibility opens an avenue for developing a theory of elastic wave propagation in continuously stratified soft sediments that fully accounts for the coupling. Elastic waves in soft sediments consist of "fast" waves propagating with velocities close to the compressional velocity and "slow" waves propagating with velocities on the order of the shear velocity. For the slow waves, the theory predicts the existence of surface waves at the ocean-sediment boundary. In the important special case of the power-law depth-dependence of shear rigidity, phase and group velocities of the interface waves are shown to scale as a certain power of frequency. An explicit, exact solution was obtained for the surface waves in sediments characterized by constant density and a linear increase of shear rigidity with depth, that is, for the case of shear speed proportional to the square root of the depth below the sediment-water interface. Asymptotic and perturbation techniques were used to extend the result to more general environments. Theoretical dispersion relations agreed well with numerical simulations and available experimental data and, as demonstrated in a companion paper [D. M. F. Chapman and O. A. Godin, J. Acoust. Soc. Am 110, 1908 (2001)] led to a simple and robust inversion of interface wave travel times for shear velocity profiles in the sediment.

Dispersion of interface waves in sediments with power-law shear speed profiles. II. Experimental observations and seismo-acoustic inversions.

The propagation of seismic interface waves is investigated in soft marine sediments in which the density is constant, the shear modulus is small, and the profile of shear speed c(s) versus depth z is of the power-law form c(s) (z) = c0z(v), in which c0 and v are constants (0< v < 1). Both the phase speed V and the group speed U of interface waves scale with frequency as f(v/(v -1)) and they obey the simple relation U= (1 - v) V. These relations are derived in a simple way using ray theory and the WKB method; a companion paper [O. A. Godin and D. M. F. Chapman, J. Acoust. Soc. Am. 110, 1890 (2001)] rigorously derives the same result from the solutions to the equations of motion. The frequency scaling is shown to exist in experimental data sets of interface wave phase speed and group speed. Approximate analytical formulas for the dispersion relations (phase and group speed versus frequency) enable direct inversion of the profile parameters c0 and v from the experimental data. In cases for which there is multi-mode dispersion data, the water-sediment density ratio can be determined as well. The theory applies to vertically polarized (P-SV) modes as well as to horizontally polarized (SH) modes (that is, Love waves).

Gastroesophageal reflux disease in children older than two years of age.

Since there are few studies examining gastroesophageal reflux (GER) in healthy children beyond infancy, we report our experiences treating children older than two with this condition. GER was diagnosed by either an abnormal extended intraesophageal pH monitoring (pH study) or presence of histological esophagitis. Thirty-seven patients met the criteria, ages 3 to 19 years (mean 11) and 68% were males. Common symptoms were vomiting, abdominal or chest pain, heartburn and regurgitation. Mean duration of symptoms was 28.7 months, and six patients had severe esophagitis, and one had Barrett's esophagus. Patients with severe esophagitis were older and had strongly positive pH study parameters compared to the rest of patients (p < 0.05). All patients were treated with prokinetic and acid reducing agents for 8 to 12 weeks. Sixty-two percent responded to initial course and remained asymptomatic during the follow-up period. Nissen fundoplication was recommended to five patients (13.5% of study population) because of refractory GER. Four of these patients who required surgery had severe esophagitis. In summary, GER in normal older children is a chronic disease with potentially severe complications. All patients should be evaluated by pH study and endoscopic esophageal biopsies, and have careful follow up.

Case management by physician assistants and primary care physicians vs emergency physicians.

OBJECTIVES: To determine whether physician assistants' (PAs') and primary care physicians' (PCPs') case management for 5 common primary care medical problems is similar to that of emergency physicians (EPs). METHODS: An anonymous survey was used to compare PAs, PCPs, and EPs regarding intended diagnostic and treatment options for hypothetical cases of asthma, pharyngitis, cystitis, back strain, and febrile child. Published national practice guidelines were used as a comparison criterion standard where available. The participants stated that they treated all of the patients and responded to all of the cases to be included in the survey. The responses of the PA and PCP groups were compared with those of the EP group, and financial charges for care by each group were analyzed. RESULTS: The EPs tended to follow treatment guidelines closer than did other primary care specialists. The management of PCPs and PAs differed from that of EPs, as follows: [table: see text] CONCLUSION: The EPs more closely followed clinical guidelines than did the PAs and PCPs for these standardized clinical scenarios. Although the relationship of such theoretical practice to actual practice remains unknown, use of these clinical scenarios may identify intended practice patterns warranting attention.

The nature of cuticular "ruffles" on slowly plucked anagen hair roots.

When an anagen hair is slowly plucked, the root's surface near the distal end of the keratogenous zone shows rings of 'ruffles' which are cuticular scales rolled back towards the root tip in a tight curl. During extraction, the rachet-like cuticle of the inner root sheath tears apart the almost differentiated cuticular scales on the root's cortex. Further extraction rolls up the cuticle because of the friction with the inner root sheath cuticle and because the torn intercellular cement reconstitutes so that the ruffle's curl is stabilized by cohesion (self-gluing). No evidence was found for pretensioning in the root's cuticle as an explanation for the curling.

Workforce projections for emergency medicine: how many emergency physicians does the United States need?

OBJECTIVE: To mathematically model the supply of and demand for emergency physicians (EPs) under different workforce conditions. METHODS: A computer spreadsheet model was used to project annual EP workforce supply and demand through the year 2035. The mathematical equations used were: supply = number of EPs at the beginning of the year plus annual residency graduates minus annual attrition; demand = 5 full-time equivalent positions/ED x the number of hospital EDs. The demand was empirically varied to account for ED census variation, administrative and teaching responsibilities, and the availability of physician extenders. A variety of possible scenarios were tested. These projections make the assumption that emergency medicine (EM) residency graduates will preferentially fill clinical positions currently filled by EPs without EM board certification. RESULTS: Under most of the scenarios tested, there will be a large deficit of EM board-certified EPs well into the next century. Even in scenarios involving a decreasing "demand" for EPs (e.g., in the setting of hospital closures or the training of physician extenders), a significant deficit will remain for at least several decades. CONCLUSIONS: The number of EM residency positions should not be decreased during any restructuring of the U.S. health care system. EM is likely to remain a specialty in which the supply of board-certified EPs will not meet the demand, even at present levels of EM residency output, for the next several decades.

Open thoracotomy procedural competency: validity study of teaching and assessment modalities.

STUDY OBJECTIVES: To determine (1) reliability and validity estimates of three modalities used to assess open thoracotomy procedural competency and (2) the effect of computer practice on procedural performance as measured by the three assessment modalities. METHODS: An experimental, sequential assessment design with volunteer examinees completing all three assessment modalities (paper, computer, pig model) was implemented at the animal support facilities of a university medical school with an affiliated emergency medicine residency program. Level of physician training (student, resident, faculty) and type of computer practice (thoracotomy, cricothyrotomy) were independent variables. Procedural competency scores were determined for each modality; scores were defined in terms of performance time and performance accuracy for three thoracotomy procedures (opening the chest, pericardiotomy, and aortic cross-clamping). RESULTS: Thoracotomy performance on the pig reliably discriminated among examinees known to differ in level of training. However, computer simulation performance did not significantly differ among examinees with different levels of training. Computer simulation practice significantly improved later performance on the computer assessment (P < .05) but not on the pig assessment. The greatest predictor of procedural competency (time and accuracy) on the pig assessment was the ability to sequentially order procedural steps. CONCLUSION: This study establishes the pig model as superior to the paper and computer models as the criterion standard for open thoracotomy assessment. Psychometric properties support the pig model as the most reliable and valid model yet described for assessing thoracotomy procedural competency. Computer simulation practice using visual images (complex anatomy) and the sequential ordering of procedural steps through paper modeling show promise for teaching and assessment of prerequisite skills required to develop psychomotor procedural competency.

An objective measurement of the anchoring strength of anagen hair in an adult with the loose anagen hair syndrome.

A 21-year-old male presented with the life-long symptom of slowly growing, easily extractable hair lacking sheath remnants. The distribution and density of all his hair regions appeared normal and there was no alopecia. A hair-pull test was painless and resulted in all hairs being removed, all in keeping with a diagnosis of loose anagen hair syndrome (LAHS). The trichogram was normal. Electronically measured epilation revealed values which were significantly lower than controls. His hair follicles were remarkable for this syndrome in that they looked perfectly normal with light microscopy; however, the segment of the follicle with the keratogenous zone was significantly shorter than normal. It is postulated that a subtle intercellular defect must reside in the line of shear proximal to the level of cuticular differentiation to account for the weak anchoring of the root in the follicle. A consequence of a genetic error probably causes both the weak anchoring and the slow hair growth.

Qualitative research methodologies in emergency medicine.

Qualitative research methodologies, though often used in other fields and in medical educational investigations. have not been used to study problems in emergency medicine (EM). These methodologies address qualitative data and provide a process of describing, interpreting, and explaining the dynamics of a population or phenomenon. The stages of a qualitative investigation include initial narrative description, interpretation, theory development, assessment of generalization, and evaluation. Important differences between this framework and those of quantitative research methods are described. These methods may be applied to systematic investigation of virtually any observable phenomenon or process in EM in which a better understanding of process would be valuable, such as patient flow, patient satisfaction issues, patient turnover and sign-out processes, bedside teaching, EM teamwork dynamics, and development of the career interests of students and residents. As with quantitative research, EM academicians should seek collaboration and appropriate training with guidance by established qualitative investigators when applying these methods.

Subcutaneous microvascular (capillary) calcification. Another basis for livedo-like skin changes?

A morbidly obese woman with acute renal failure, high serum phosphorus and slightly depressed serum calcium levels, developed areas of induration in the subcutis with associated livedo reticularis. Later, the subcutis became necrotic and the skin ulcerated. The arterioles, and notably widened occluded capillaries, were found to contain calcium and phosphorus as determined by energy dispersive spectrometry. X-ray diffraction of the subcutis in an early stage of this lesion showed that the mineral was most likely a poorly crystalline hydroxyapatite.

Emergency thoracotomy: comparison of medical student, resident, and faculty performances on written, computer, and animal-model assessments.

OBJECTIVE: In clinical practice, thoracotomy and other critical emergency procedures are rarely required. Consequently, medical students and residents have difficulty acquiring procedural competency in these critical procedures. The authors developed objective written, computer, and animal-model assessments of thoracotomy procedural competency to permit comparison of the reliability and validity of these three procedural assessment modalities. METHODS: Thoracotomy procedural competency was evaluated for 18 persons at three levels of training (medical student, resident, faculty), using written, computer, and animal-model assessments. A prospective, sequential assessment design was used, with the examinees serving as their own controls. Procedural competency was defined in terms of performance time (animal time scale) and performance accuracy (written accuracy, computer accuracy, and animal accuracy scales) for three thoracotomy procedures (opening the chest, pericardiotomy, and aortic cross-clamping). Level of training was the independent variable, and procedural competency scores were the outcome measures. Confounding variables included previous thoracotomy and computer experience. RESULTS: Computer and animal-model assessments produced reliable results (Chronbach's alpha > 0.50). The animal time scale and computer accuracy scale best reflected the expected skill differences among levels of physician training, providing support for construct validity. In contrast, written and animal accuracy scale scores did not significantly differ by level of physician training. Moreover, previous thoracotomy experience (i.e., number of procedures previously performed) was not a significant predictor of procedural competency. CONCLUSIONS: This study demonstrates that critical emergency medicine procedures can be evaluated reliably and validly using computer simulation and animal-model assessments. Neither previous thoracotomy experience nor knowledge of procedure content adequately predicts thoracotomy competency.