Propagation of Gaussian Schell-model beams in modulated graded-index media.

The evolution of partially coherent beams in longitudinally modulated graded-index media is studied. The special cases of Gaussian Schell-model beams and parametric modulation, when the modulation period is half the fiber self-imaging period, are examined in detail. We show that the widths of the intensity and coherence of Gaussian Schell-model beams undergo amplification in parametrically modulated parabolic graded-index media. The process is an analog of quantum mechanical parametric amplification and generation of squeezed states. Our work may find application in spatial and temporal imaging of partially coherent beams in fiber-based imaging systems.

General medicine and surgery for dental practitioners: part 5. Immunological disease and dental practice.

At some stage in clinical practice all dental practitioners will encounter patients with disorders of the immune system. It is therefore important that dental practitioners are aware of the potential implications for safe practice. This paper summarises some of the more common immunological disorders that may be encountered, together with a basic review of immunological processes from a clinical perspective.

Resonance in quantum dot fluorescence in a photonic bandgap liquid crystal host.

Microcavity resonance is demonstrated in nanocrystal quantum dot fluorescence in a one-dimensional (1D) chiral photonic bandgap cholesteric-liquid crystal host under cw excitation. The resonance demonstrates coupling between quantum dot fluorescence and the cholesteric microcavity. Observed at a band edge of a photonic stop band, this resonance has circular polarization due to microcavity chirality with 4.9 times intensity enhancement in comparison with polarization of the opposite handedness. The circular-polarization dissymmetry factor g(e) of this resonance is ~1.3. We also demonstrate photon antibunching of a single quantum dot in a similar glassy cholesteric microcavity. These results are important in cholesteric-laser research, in which so far only dyes were used, as well as for room-temperature single-photon source applications.

Phase-locked laser system for use in atomic coherence experiments.

We describe a phase-coherent laser system designed for use in experiments involving coherently prepared atomic media. We implement a simple technique based on a sample-and-hold circuit together with a reset of the integrating electronics that makes it possible to scan continuously the relative frequency between the lasers of over tens of gigahertz while keeping them phase locked. The system consists of three external-cavity diode lasers operating around 795 nm. A low-power laser serves as a frequency reference for two high-power lasers which are phased locked with an optical phase-locked loop. We measured the residual phase noise of the system to be less than 0.04 rad(2). In order to show the application of the system towards atomic coherence experiments, we used it to implement electromagnetically induced transparency in a rubidium vapor cell and obtained a reduction in the absorption coefficient of 92%.

Joint contact characteristics in agility total ankle arthroplasty.

High component contact pressures in total joint prostheses can lead to particle wear debris and prosthesis loosening. The contact pressures in the Agility total ankle prosthesis have not been investigated. In the current study, a cadaveric model was used to evaluate contact characteristics (average contact area, contact pressure, and contact peak pressures) for the Agility total ankle system. Ten cadaveric specimens were implanted with the Agility total ankle and axially loaded to 700 N. The average contact pressure of the system was 5.6 MPa with mean peak pressures of 21.2 MPa. In a separate phase of the study, contact characteristics with applied loads for each of the six component sizes showed a significant effect of component size on contact characteristics. When physiologic ankle forces are considered for normal patient activity, peak pressures observed in the current study may exceed recommended contact pressures (10 MPa) and the compressive yield point (13-22 MPa) for polyethylene. A heavy patient with a small ankle would not be expected to have a good outcome based on the current contact pressures data, whereas a heavy patient with a larger ankle might be a better candidate for surgery.

Direct measurements of urban OH reactivity during Nashville SOS in summer 1999.

Emissions of volatile chemicals control the hydroxyl radical (OH), the atmosphere's main cleansing agent, and thus the production of secondary pollutants. Accounting for all of these chemicals can be difficult, especially in environments with mixed urban and forest emissions. The first direct measurements of the atmospheric OH reactivity, the inverse of the OH lifetime, were made as part of the Southern Oxidant Study (SOS) at Cornelia Fort Airpark in Nashville, TN in summer 1999. Measured OH reactivity was typically 11 s(-1). Measured OH reactivity was 1.4 times larger than OH reactivity calculated from the sum of the products of measured chemical concentrations and their OH reaction rate coefficients. This difference is statistically significant at the 1sigma uncertainty level of both the measurements and the calculations but not the 2sigma uncertainty level. Measured OH reactivity was 1.3 times larger than the OH reactivity from a model that uses measured ambient concentrations of volatile organic compounds (VOCs), NO, NO2, SO2, and CO. However, it was within approximately 10% of the OH reactivity from a model that includes hydrocarbon measurements made in a Nashville tunnel and scaled to the ambient CO at Cornelia Fort Airpark. These comparisons indicate that 30% of the OH reactivity in Nashville may come from short-lived highly reactive VOCs that are not usually measured in field intensive studies or by US EPA's Photochemical Assessment Monitoring Stations.

Proprioception of the knee before and after anterior cruciate ligament reconstruction.

PURPOSE: The purpose of this study was to determine, first, if there is measurable deficit in proprioception in an anterior cruciate ligament (ACL)-deficient knee, either compared to the contralateral knee or external controls; second, if this deficit, if present, improves after ACL reconstruction; and third, if improvement occurs, what the time course of improvement is. TYPE OF STUDY: Prospective cohort study. METHODS: Patients undergoing ACL reconstruction at the University of Chicago, demonstrating a full and painless range of motion and no other knee ligament injury or history of previous knee surgery, were eligible. Twenty-six patients, with an average age of 25 years (range, 16 to 48) were enrolled. Average time from injury to reconstruction was 8 weeks. The patients' contralateral knee served as an internal control, and 26 age-matched and gender-matched healthy volunteers were enrolled as an external control group. ACL reconstructions were performed using a single-incision technique with either bone-patellar tendon-bone or quadrupled hamstring autograft. They were allowed immediate weightbearing as tolerated and participated in a standardized rehabilitation program, with the goal of returning to sport at approximately 6 months. Proprioception testing was carried out using an electrogoniometer, in a seated position. Joint position sense (JPS) and threshold to detection of passive motion (TDPM) were measured preoperatively and at 3 and 6 weeks and 3 and 6 months postoperatively. RESULTS: Mean KT-2000 values 6 months postoperatively were 1.38 mm (+/-2). Modified Lysholm score improved significantly (P <.01). Calculated r values were 0.65 for JPS and 0.96 for TDPM. No significant differences in postoperative proprioception were found between hamstring and patellar tendon grafts or among patients with meniscus injury, meniscus repair, or chondral injury. Preoperatively, the mean TDPM in both the injured and contralateral knees was significantly higher (worse) than in the external control knees (P =.008; P =.016). Evaluation of changes in proprioception from preoperative to 6 months postoperative showed significant improvement in both injured and contralateral knees (P =.04; P =.01). At 6-month follow-up, there was no significant difference from controls. CONCLUSIONS: TDPM was a more reliable method than JPS for testing proprioception before and after ACL reconstruction in this study. Bilateral deficits in knee joint proprioception (TDPM) were documented after unilateral ACL injury. Reconstruction of a mechanical restraint (ACL graft) was believed to have a significantly positive impact on early and progressive improvement in proprioception.

Arthroscopic arthrodesis of the ankle, subtalar, and first metatarsophalangeal joint.

Arthroscopy of the foot and ankle should become part of the armamentarium of the foot and ankle surgeon. An arthroscopic fusion procedure of the ankle, subtalar, or first MTP joint is a viable alternative in certain patients. Appropriately selected patients (i.e., those with minimal bony deformity and without significant bone defects or avascular bone) can expect fusion rates at least equivalent to the standard open procedure. The benefits are truly magnified when one considers that these procedure result in a shortened hospitalization time, less pain as a result of the minimal surgical dissection and soft tissue stripping, and faster rehabilitation times. As results in the literature become available, these procedures can be expected to become an acceptable means of achieving the desired treatment goals.

Honeycomb pattern formation by laser-beam filamentation in atomic sodium vapor.

We have observed transverse pattern formation leading to highly regular structures in both the near and far fields when a near-resonant laser beam propagates without feedback through an atomic sodium vapor. One example is a regular far-field honeycomb pattern, which results from the transformation of the laser beam within the vapor into a stable three-lobed structure with a uniform phase distribution and highly correlated power fluctuations. The predictions of a theoretical model of the filamentation process are in good agreement with these observations.

Absorbable implants in fracture management.

The use of absorbable implants has been studied extensively in the clinic and the laboratory. The limitations of absorbable implants are now well-known and include a finite life span and strength profile, the possible development of an inflammatory response, and their limitation to use in fractures that do not require traditional compression techniques. Advantages of these implants include the lack of necessity for removal at a later date, which has cost savings potential, their ease of use, and their strength, which may be sufficient for healing in certain situations. The most likely scenarios for the use of these implants in fracture management of the foot and ankle include syndesmotic disruptions, dislocations about the midfoot, and fractures of the medial malleolus.

Optimal surgical preparation of the residual limb for prosthetic fitting in below-knee amputations.

A well-performed below-knee amputation can result in a high level of patient satisfaction and function. The potential for a successful result and independent ambulation is good after a transtibial amputation, with approximately 70% to 100% of patients being able to ambulate independently after this procedure. A properly fitted and appropriately designed prosthesis is integral to the achievement of these goals. The approaches and techniques discussed here are essential in optimally preparing the residual limb for prosthetic fitting. Attention to factors such as the preoperative evaluation and the surgical technique can ensure the best possible outcome for amputation patients.

Complete paraplegia as a result of regional anesthesia.

Complications after spinal or epidural anesthesia are rare. We report 2 cases of postoperative, complete paraplegia after regional anesthesia in orthopaedic patients not on anticoagulants. The paralysis was likely the result of spinal cord compression secondary to an epidural hematoma in 1 case and subdural hematoma in 1 case. A review of the literature regarding complications of regional anesthesia is presented. Regional anesthesia should be administered with caution and in selected patients.

Imaging of osteochondral lesions of the talus.

A review of the literature reveals that all studies have been performed retrospectively. These studies have included limited numbers of low-grade lesions and no prospective, randomized, comparison studies have been performed to suggest the superiority of CT scanning over MR imaging. The following conclusions, however, can be made. Plain radiographs are useful in the initial evaluation of patients with acute or chronic complaints of ankle pain and swelling. These initial studies, however, may not identify all osteochondral lesions of the talus, particularly lower grade lesions. CT scanning can accurately identify and localize a lesion while defining its extent. It has been suggested that CT scanning can be used to assess whether bony healing has occurred at follow-up. MR imaging can also precisely identify, localize, and define an OLT with the advantage of assessing the integrity of the overlying cartilage. It can detect lower grade lesions with improved sensitivity and may aid in the differentiation of Stage II and Stage III lesions. Using the preceding observations, the following approach is recommended in the evaluation and work-up of an osteochondral lesion of the talus (Fig. 7). The patient who presents with ankle pain and swelling should have weight-bearing radiographs of the ankle obtained. If these films demonstrate an osteochondral lesion of the talus, staging of the lesion should be performed. In lesions that appear nondisplaced on plain radiography (low grade; stable), MR imaging is recommended so the clinician can evaluate the integrity of the overlying cartilage and assess the true stability of the lesion. In lesions that appear displaced on plain radiography (high grade; unstable), the CT scan is the preferred modality in order to provide accurate assessment of lesion size and location. It should be noted, however, that no study has prospectively [figure: see text] compared the efficacy of these two modalities in the evaluation of osteochondral lesions. If a symptomatic patient presents with negative plain films, then an initial period of immobilization using a cast or boot brace is recommended. This is followed by joint mobilization and range of motion exercises. If the patient remains symptomatic at the 4 to 6 week followup period, then an MR image should be performed. This study provides information regarding soft-tissue impingement, proliferative synovitis, and other bony and soft-tissue pathology. The authors have found that despite the results of bone scintigraphy, an MR image is invariably obtained. Because of this the authors do not recommend bone scintigraphy in the evaluation and diagnosis of OLT.

Pseudoaneurysm of the lateral malleolar artery after an ankle sprain: case report and review of the literature.

A pseudoaneurysm of the peroneal artery or one of its branches is rare after trauma. The diagnosis is frequently delayed, resulting in substantial morbidity to the patient. The infrequent occurrence of this condition has resulted in a lack of diagnostic and treatment guidelines. However, when recognized, prompt attention involving either surgical ligation or embolization of the injured arterial branch is the most reliable method of treatment. Presented is a report of a patient who developed a lateral malleolar arterial pseudoaneurysm after an ankle sprain, which was treated successfully with aneurysmal excision and surgical ligation of the injured arterial branch. A review of the literature and treatment recommendations follow.

Direct measurement of a photoconductive receiver's temporal response by dithered-edge sampling.

We present the results of a direct measurement of the temporal response of a terahertz (THz) photoconductive receiver obtained by dithered-edge sampling. The receiver response has structure that accounts for the negative-going leading edge of the pulse shape that is often seen in measurements made with these receivers in a conventional sampling arrangement. We show that the THz pulse shape measured by conventional photoconductive sampling is indeed a cross correlation of the pulse with the measured receiver's response.

Randomised controlled trial of L-carnitine as a nutritional supplement in preterm infants.

AIMS: To evaluate the effect of L-carnitine supplementation (25 mg/kg/d) on the growth and incidence of hypoglycaemia in preterm infants. METHODS: A double blind, placebo controlled randomised trial, stratified for gestational age, was conducted of 86 preterm infants between 28 and 34 gestational weeks. The median gestational ages in the carnitine group and placebo groups were 30.7 weeks (range 28.0 to 33.6) and 31.4 weeks (range 28.0 to 33.9), respectively. The median birthweights were 1.557 kg (range 0.944 to 2.275) and 1.645 kg (range 0.885 to 2.545), respectively. RESULTS: Mean plasma free carnitine concentrations were below values for normal term infants in both groups on day 1 (carnitine group 44.8 mumol/l, placebo group 25.5 mumol/l) in the placebo group on day 7 (50.7 mumol/l), but in neither group on days 14 and 28. Total, free, and acylcarnitine concentrations were significantly increased in both urine and blood in the L-carnitine group. There was no significant difference between the placebo and carnitine supplemented groups in growth rate, as assessed by weight, length, skinfold thickness and head circumference measurements, or in the incidence of episodes of hypoglycaemia. CONCLUSION: The addition of carnitine as a nutritional supplement at a dose of 25 mg/kg/day did not improve growth in our group of preterm infants nor protect them from episodes of hypoglycaemia.

A commercial pregnancy test modified for field studies of fetal loss.

We describe simple modifications to the ICON II hCG (URINE) pregnancy test to provide a sensitive and specific urinary assay for hCG in field studies of fetal loss. The modified assay had a qualitative lower limit of detection of 0.30 IU/l, a 50% qualitative limit of 0.61 IU/l, a 100% qualitative limit of 1.16 IU/l, and a quantitative limit of 0.80 IU/l. Coefficients of variation ranged from 9.9% to 21.1%. Parallelism was observed among serially diluted subject samples. We used the assay in an 11-month prospective study of fetal loss in rural Bangladesh in which urine samples were collected twice-weekly from 494 women; 330 pregnancies and 93 fetal losses were detected. The median time to a positive pregnancy diagnosis was day 26 from last menses. The modified assay provided qualitative detection of early pregnancy comparable to laboratory assays, and appears to be well suited for use in epidemiologic or rural-population fetal loss studies.