Evaluation of the robustness of polarization attraction for 10.7-GBaud NRZ-BPSK after long-haul 100-GHz DWDM transmission.

An investigation was carried out on the polarization attraction (PA) of a polarization-scrambled 10.7-GBaud NRZ-BPSK signal in a 1-km-long highly nonlinear fiber (HNLF). For the back-to-back case, PA on an ASE-loaded signal yielded a receiver sensitivity penalty of ≈ 14.5 dB at the ITU-T G.975.1.I3 FEC threshold of 3.5 × 10-3, relative to matched-filter reception theory. After long-haul 100-GHz DWDM transmission in a recirculating loop, PA on the output signal was found to achieve approximately the same receiver sensitivity performance, as that of the back-to-back case. From these experiments, it is concluded that the Gordon-Mollenauer effect due to propagation in the HNLF during PA dominates other impairments including those arising from the long-haul 100-GHz DWDM recirculating loop transmission.

Higher incidence of HCV in females compared to males who inject drugs: A systematic review and meta-analysis.

Women who inject drugs have been shown to have higher incidence of HIV and risk behaviours than men, but there are conflicting reports about hepatitis C virus (HCV) incidence. We systematically reviewed the literature to examine the female-to-male (F:M) HCV incidence in female and male persons who inject drugs (PWID), and also to explore the heterogeneity (i.e. methodological diversity) in these differences. We searched PubMed and EMBASE for studies published between 1989 and March 2015 for research that reported incidence of HCV infection by sex or HCV incidence F:M rate ratio. A total of 28 studies, which enrolled 9325 PWID, were included. The overall pooled HCV incidence rate (per 100 person-years observation) was 20.36 (95% CI: 13.86, 29.90) and 15.20 (95% CI: 10.52, 21.97) in females and males, respectively. F:M ratio was 1.36:1 (95% CI: 1.13, 1.64) with substantial heterogeneity (I-squared=71.6%). The F:M ratio varied by geographic location from 4.0 (95% CI: 1.80, 8.89) in China to 1.17 (95% CI: 0.95, 1.43) in the U.S. In studies which recruited participants from community settings, the F:M ratio was 1.24 (95% CI: 1.03, 1.48), which was lower than that reported in the clinical settings (1.72, 95% CI: 0.86, 3.45). The number of studies included provided sufficient statistical power to detect sex differences in this analysis. Our findings raise questions and concerns regarding sex differences with respect to the risk of HCV. Both behavioural and biological studies are needed to investigate causes and potential mechanisms as well as sex-specific prevention approaches to HCV infection.

Polarization attraction of 10-Gb/s NRZ-BPSK signal in a highly nonlinear fiber.

Polarization attraction of a 10-Gb/s non-return-to-zero binary phase-shift keyed (NRZ-BPSK) signal has been successfully demonstrated for the first time in a counter-propagating beam configuration using a continuous-wave pump, in a highly nonlinear fiber, by utilizing the Kerr nonlinear cross-polarization process inherent to that fiber. The efficacy of mitigating polarization-dependent loss across polarization-sensitive devices was emulated with a linear polarizer located before the receiver. The receiver sensitivity penalty at 10-9 bit-error-rate relative to the baseline NRZ-BPSK signal was < 0.5 dB, when polarization attraction was employed for a polarization-scrambled signal (after achieving a degree of polarization > 90%). The results confirm that polarization attraction is independent of modulation format.

Polarization-insensitive all-optical dual pump-phase transmultiplexing from 2 × 10-GBd OOKs to 10-GBd RZ-QPSK using cross-phase modulation in a birefringent nonlinear PCF.

Polarization-insensitive (PI) all-optical dual pump-phase transmultiplexing from 2 × 10-GBd OOKs to 10-GBd RZ-QPSK was successfully demonstrated in a birefringent nonlinear photonic crystal fiber (PCF), by utilizing cross-phase modulation (XPM) and the inherent birefringence of the device, for the first time. PI operation was achieved by launching the probe and one pump off-axis while the state of polarization (SOP) of the other pump was randomized. Optimum pump-probe detuning, all within the C-Band, was also utilized to reduce the polarization-induced power fluctuation. Receiver sensitivity penalty at 10-9 bit-error-rate was < 5.5 dB in PI operation, relative to the FPGA-precoded RZ-DQPSK baseline.

All-optical amplitude-phase transmultiplexing of RZ-OOK and RZ-BPSK to RZ-QPSK by polarization-insensitive XPM using a nonlinear birefringent AlGaAs waveguide.

Polarization-insensitive (PI) phase-transmultiplexing (PTM) of a 10-Gb/s return-to-zero ON-OFF keying (RZ-OOK) pump and a 10-Gb/s RZbinary phase-shift keying (RZ-BPSK) probe to 20-Gb/s RZ-quadrature-PSK (RZ-QPSK) has been successfully demonstrated for the first time in a passive, birefringent AlGaAs waveguide, utilizing PI cross-phase modulation (PI-XPM). For differential QPSK (DQPSK)-detection, a 10 − 9-BER pre-amplified receiver sensitivity penalty of ≈ 2.5 dB for the in-phase component and ≈ 4.9 dB for the quadrature component were found. The penalties were relative to the FPGA-precoded RZ-DQPSK baseline for a pump-probe detuning of ≈ 12 nm, when the probe state of polarization was scrambled and the pump was launched off-axis into the waveguide.

Spurious mode reduction in dual injection-locked optoelectronic oscillators.

Optoelectronic oscillators (OEOs) are promising sources of low phase noise radio frequency (RF) signals. However, at X-band frequencies, the long optical fiber delay line required for a high oscillator Q also leads to spurious modes (spurs) spaced too narrowly to be filtered by RF filters. The dual injection-locked OEO (DIL-OEO) has been proposed as a solution to this problem. In this work, we describe in detail the construction of a DIL-OEO. We also present experimental data from our systematic study of injection-locking in DIL-OEOs. With this data, we optimize the DIL-OEO, achieving both low phase noise and low spurs. Finally, we present data demonstrating a 60 dB suppression of the nearest-neighbor spur without increasing the phase noise within 1 kHz of the 10 GHz central oscillating mode.

Theoretical investigation of polarization-insensitive data format conversion of RZ-OOK to RZ-BPSK in a nonlinear birefringent fiber.

Polarization-insensitive conversion of return-to-zero (RZ) ON-OFF keying (RZ-OOK) to RZ binary phase-shift keying (RZ-BPSK) has been achieved by cross-phase modulation (XPM) in a nonlinear birefringent fiber. This work presents a theoretical analysis of the dependence of format conversion on pump-probe detuning, and the pump state-of-polarization (SOP) that can fluctuate unpredictably in a realistic system. An investigation of the impact of pump polarization fluctuation on receiver sensitivity and receiver optimal threshold for the converted RZ-BPSK probe is also carried out. It was found that although the desired XPM-induced pi phase shift can be achieved by launching both the RZ-OOK pump and the probe along the same birefringent axis of the fiber, the phase shift degrades to pi/3 if the SOP of the RZ-OOK pump unpredictably switches to the other axis of the fiber, resulting in a large receiver sensitivity penalty fluctuation of 14 dB. By contrast, launching the probe at 45 degrees relative to the birefringent axes can reduce the polarization-dependent receiver sensitivity penalty fluctuation to about 2 dB as the SOP of the RZ-OOK pump is swept over the Poincaré sphere. These conclusions are in good agreement with recently.

Polarization-insensitive, 40 Gb/s wavelength and RZ-OOK-to-RZ-BPSK modulation format conversion by XPM in a highly nonlinear PCF.

Polarization-insensitive wavelength conversion, as well as the conversion of return-to-zero (RZ) ON-OFF keying (RZ-OOK) to RZ binary phase-shift keying (RZ-BPSK), has been simultaneously achieved at 40 Gb/s for the first time by cross-phase modulation (XPM) in a highly birefringent, nonlinear photonic crystal fiber (PCF). A 10-9-BER receiver sensitivity conversion penalty of < 3 dB was achieved for a polarization scrambled, 40 Gb/s 25%-RZ-OOK pump, when the 40 Gb/s RZ probe was launched at 45 degrees with respect to the birefringence axes of the PCF and when the pump-probe detuning was greater than about 6 nm.

Sensing oxygen through skin using a red diode laser and fluorescence lifetimes.

The most difficult impediments to transcutaneous optical sensing are the absorbance and scatter of light caused by skin and the lack of fluorescent sensing probes which can be excited at wavelengths over 600 nm. Furthermore, current optical sensing techniques rely on absorbance or fluorescence intensity measurements, both of which are sensitive to drifts in lamp intensity, changes in probe concentration and inner filter effects. We demonstrate oxygen sensing through a layer of skin by using red light which readily penetrates skin as diffusely scattered light. The oxygen sensitive osmium-ligand complex used in this study can be excited at 635-680 nm. In addition, we measure fluorescence lifetimes, which are inherently unaffected by factors that limit absorbance and fluorescence intensity measurements. By using phase fluorimetry and long lived fluorophores, we are able to demonstrate the potential for subdermal oxygen sensing with simple and inexpensive instrumentation. This work describes a paradigm for future non-invasive measurements of other analytes.

Insurance aspects of DRG outlier payments.

As part of the prospective payment system, the government pays 'outlier' payments for especially long or expensive cases. These payments can be viewed as insurance for the hospital against excessive losses. They mitigate problems of access and underprovision of care for the sickest patients, and provide additional payments to the hospitals that take care of them, thereby making payments to hospitals more equitable. This paper characterizes the outlier payment formulae that minimize risk for hospitals under any fixed constraints on the sum of outlier payments and minimum hospital coinsurance rate. We then simulate per-case payments for a policy that did not include any outlier payments, the current outlier policy, and several other policies that minimize risk subject to different coinsurance constraints. The current outlier policy achieves each of its goals to at least some extent, but more insurance could be provided without lessening attainment of the other goals. We also discuss some problems with the implementation of the current policy, such as its reliance on day outliers.

How much change in the case mix index is DRG creep?

We re-abstracted a nationally representative sample of 7,887 Medicare charts to determine how much of the change in Medicare's Case Mix Index between 1986 and 1987 was true change in the complexity of cases and how much was upcoding or 'DRG creep'. About two-thirds of the change is true. Most of the remaining third is attributable to a general change in the completeness of coding; some is attributable to changes in the Grouper program. Thus, most of the additional $1 billion paid to hospitals because of the Case Mix Index change appears justified by the additional complexity of patients hospitalized.

A longitudinal comparison of charge-based weights with cost-based weights.

The diagnosis-related group weights that determine prices for Medicare hospital stays are recalibrated annually using charge data. Using data from fiscal years 1985 through 1987, the authors show that differences between these charge-based weights and cost-based weights are increasing only slightly. Charge-based weights are available in a more timely manner and, based on temporal changes in the weights, we show that this is an important consideration. Charge-based weights provide higher payments than cost-based weights to hospitals with higher case-mix indexes, but have little effect on hospitals with low cost-to-charge ratios, high capital costs, or high teaching costs.

Assessing the FY 1989 change in Medicare PPS outlier policy.

In fiscal year (FY) 1989, Medicare changed its rules for paying for extremely long or expensive hospital stays called "outliers." We compared outlier payments in FYs 1989 and 1988, after adjusting for other simultaneous policy changes. We found that the new policy succeeded in targeting more outlier payments to the most expensive cases and to the hospitals suffering larger prospective payment system (PPS) losses and in reducing hospital financial risk. Using time-series analyses, we show that the policy change had no measurable effect on the timing of discharges or on the concentration of expensive cases in urban government-owned hospitals.

How recalibration method, pricing, and coding affect DRG weights.

We compared diagnosis-related group (DRG) weights calculated using the hospital-specific relative-value (HSRV) methodology with those calculated using the standard methodology for each year from 1985 through 1989 and analyzed differences between the two methods in detail for 1989. We provide evidence suggesting that classification error and subsidies of higher weighted cases by lower weighted cases caused compression in the weights used for payment as late as the fifth year of the prospective payment system. However, later weights calculated by the standard method are not compressed because a statistical correlation between high markups and high case-mix indexes offsets the cross-subsidization. HSRV weights from the same files are compressed because this methodology is more sensitive to cross-subsidies. However, both sets of weights produce equally good estimates of hospital-level costs net of those expenses that are paid by outlier payments. The greater compression of the HSRV weights is counterbalanced by the fact that more high-weight cases qualify as outliers.

Medicare case-mix index increase.

Medicare paid hospitals a higher amount per admission in 1984 than had been planned because the case-mix index (CMI), which reflects the proportion of patients in high-weighted DRG's versus low-weighted ones, increased more than had been projected. This study estimated the degree to which the increase in the CMI from 1981 reflected medical practice changes, the aging of the Medicare inpatient population, changes in coding practices of physicians and hospitals, and changes in the way that the Health Care Financing Administration collects the data on case-mix. All of the above, except for aging, contributed to the increase in the CMI.

Modified capitation and treatment incentives for end stage renal disease.

This study developed a modified capitation payment method for the Medicare end stage renal disease (ESRD) program designed to support appropriate treatment choices and protect health plans from undue financial risk. The payment method consists of risk-adjusted monthly capitated payments for individuals on dialysis or with functioning kidney grafts, lump sum event payments for expected incremental costs of kidney transplantations or graft failures, and outlier payments for expensive patients. The methodology explained 25 percent of variation in annual payments per patient. Risk adjustment captured substantial variations across patient groups. Outlier payments reduced health plan risk by up to 15 percent.

Use of diagnosis-related groups by non-Medicare payers.

Medicare's prospective payment system (PPS) for hospital cases is based on diagnosis-related groups (DRGs). A wide variety of other third-party payers for hospital care have adapted elements of this system for their own use. The extent of DRG use varies considerably both by type of payer and by geographical area. Users include: 21 State Medicaid programs, 3 workers' compensation systems, the Civilian Health and Medical Program of the Uniformed Services (CHAMPUS), more than one-half of the Blue Cross and Blue Shield Association (BCBSA) member plans, several self-insured employers, and a few employer coalitions. We describe how each of these payers use DRGs. No single approach is dominant. Some payers negotiate specific prices for so many combinations of DRG and hospital that the paradigm that payment equals rate times weight does not apply. What has emerged appears to be a very flexible payment system in which the only constant is the use of DRGs as a measure of output.

A clinically detailed risk information system for cost.

The authors discuss a system that describes the resources needed to treat different subgroups of the population under age 65, based on burden of disease. It is based on 173 conditions, each with up to 3 severity levels, and contains models that combine prospective diagnoses with retrospectively determined elements. We used data from four different payers and standardized the cost of most services. Analyses showed that the models are replicable, are reasonably accurate, explain costs across payers, and reduce rewards for biased selection. A prospective model with additional payments for birth episodes and for serious problems in newborns would be an effective risk adjuster for Medicaid programs.

Where is the financial safety net for managed care physicians?

OBJECTIVE: Empiric research on mechanisms by which managed care physicians attempt to mitigate financial risk is lacking. We assumed the perspective of a managed care plan in investigating the relationship between risk sharing and the match between a physician's capitation payments and costs of care. DESIGN: The study design was a family of payment simulations using 2 years of managed care claims data. METHODS: Claims from a cohort of 82,525 managed care patients were used, with year 1 data determining a capitation rate for year 2 primary care services. The net provider payment in year 2 was examined under scenarios that might modify financial outcomes, including stop-loss insurance, age- and gender-adjustment of capitation, and risk pooling within independent practice associations. RESULTS: The size of a provider's patient panel was positively correlated with net per capita payment (r = 0.22; P < 0.0001 without risk modification strategies). The variance of the ratio of net to total revenue was utilized as a proxy for the degree of risk assumed in caring for a panel of capitated enrollees. Risk modification strategies reduced this variance measure, with risk pooling producing the largest effect, especially for providers of panels of fewer than 135 patients. In contrast, age- and gender-adjustment of capitation payments had little effect on reimbursement outcomes. CONCLUSIONS: Short of increasing the pool of capitated patients, risk modification strategies appear limited in their ability to produce more equitable reimbursement to providers with small patient panels. With many providers assuming substantial risk in pursuing managed care contracts, these dynamics may favor organizational forms of medical practice that facilitate large patient panels within a single plan.

Oxygen consumption for lower extremity exercises in normal subjects and burned patients.

The purpose of this study was to compare the oxygen requirements for normal subjects and burned patients during rest and while performing two separate exercises of the quadriceps femoris muscles. The oxygen consumption of 10 normal subjects and 10 burned patients while at rest and while performing each exercise was measured. The resting and exercising oxygen-consumption levels for burned patients were significantly greater (p < .01) than for normal subjects. However, the mean difference in increased oxygen consumption during two exercises for normal subjects and for burned patients was not significant (p > .05). The elevated resting and exercising oxygen-consumption levels in burned patients were considered to be related to the hypermetabolic response characteristic of thermally injured patients.