Antenna gain of actively compensated free-space optical communication systems under strong turbulence conditions.

Current Strehl ratio models for actively compensated free-space optical communications terminals do not accurately predict system performance under strong turbulence conditions as they are based on weak turbulence theory. For evaluation of compensated systems, we present an approach for simulating the Strehl ratio with both low-order (tip/tilt) and higher-order (adaptive optics) correction. Our simulation results are then compared to the published models and their range of turbulence validity is assessed. Finally, we propose a new Strehl ratio model and antenna gain equation that are valid for general turbulence conditions independent of the degree of compensation.

Laser differential image-motion monitor for characterization of turbulence during free-space optical communication tests.

A laser differential image-motion monitor (DIMM) system was designed and constructed as part of a turbulence characterization suite during the DARPA free-space optical experimental network experiment (FOENEX) program. The developed link measurement system measures the atmospheric coherence length (r0), atmospheric scintillation, and power in the bucket for the 1550 nm band. DIMM measurements are made with two separate apertures coupled to a single InGaAs camera. The angle of arrival (AoA) for the wavefront at each aperture can be calculated based on focal spot movements imaged by the camera. By utilizing a single camera for the simultaneous measurement of the focal spots, the correlation of the variance in the AoA allows a straightforward computation of r0 as in traditional DIMM systems. Standard measurements of scintillation and power in the bucket are made with the same apertures by redirecting a percentage of the incoming signals to InGaAs detectors integrated with logarithmic amplifiers for high sensitivity and high dynamic range. By leveraging two, small apertures, the instrument forms a small size and weight configuration for mounting to actively tracking laser communication terminals for characterizing link performance.

High-sensitivity DPSK receiver for high-bandwidth free-space optical communication links.

A high-sensitivity modem and high-dynamic range optical automatic gain controller (OAGC) have been developed to provide maximum link margin and to overcome the dynamic nature of free-space optical links. A sensitivity of -48.9 dBm (10 photons per bit) at 10 Gbps was achieved employing a return-to-zero differential phase shift keying based modem and a commercial Reed-Solomon forward error correction system. Low-noise optical gain was provided by an OAGC with a noise figure of 4.1 dB (including system required input loses) and a dynamic range of greater than 60 dB.

Longitudinal Evaluation of Cerebellar Signs of H-ABC Tubulinopathy in a Patient and in the taiep Model.

Hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC) is a central neurodegenerative disease due to mutations in the tubulin beta-4A (TUBB4A) gene, characterized by motor development delay, abnormal movements, ataxia, spasticity, dysarthria, and cognitive deficits. Diagnosis is made by integrating clinical data and radiological signs. Differences in MRIs have been reported in patients that carry the same mutation; however, a quantitative study has not been performed so far. Our study aimed to provide a longitudinal analysis of the changes in the cerebellum (Cb), corpus callosum (CC), ventricular system, and striatum in a patient suffering from H-ABC and in the taiep rat. We correlated the MRI signs of the patient with the results of immunofluorescence, gait analysis, segmentation of cerebellum, CC, and ventricular system, performed in the taiep rat. We found that cerebellar and callosal changes, suggesting a potential hypomyelination, worsened with age, in concomitance with the emergence of ataxic gait. We also observed a progressive lateral ventriculomegaly in both patient and taiep, possibly secondary to the atrophy of the white matter. These white matter changes are progressive and can be involved in the clinical deterioration. Hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC) gives rise to a spectrum of clinical signs whose pathophysiology still needs to be understood.

Bowel obstruction due to video capsule endoscopy in a patient with Crohn's disease.

BACKGROUND: The retention of the endoscopic capsule (EC) is a serious complication and exceptionally, acute intestinal obstruction is conditioned. CLINICAL CASE: 64 years-old man, previously treated by gastroenterology for Crohn's disease. With good initial response to pharmacological treatment for 6 weeks, subsequently with the onset of pain and symptoms not explained by colonoscopy. EC was performed, presenting at 48 hours bowel obstruction symptoms with data of systemic inflammatory response and peritoneal irritation. Exploratory laparotomy with bowel resection and side-to-side stapled anastomosis was performed, histopathology report confirmed obstruction of the bowel lumen due to impacted EC in ileal stenosis area. In the immediate postoperative period with good evolution. At 8 weeks of the procedure, he went for an enterocutaneous fistula, which had a good response to conservative treatment. CONCLUSION: The rate of retention of CE in Crohn's disease is 5-6%, prior to its use, it is recommended to perform imaging studies to evaluate the bowel permeability, however negative studies do not exclude the presence of stenosis. In cases where intestinal resection is indicated, it is recommended to be wide with side-to-side stapled anastomosis to reduce the risk of recurrence of the disease.

ANTECEDENTES: La retención de la cápsula endoscópica (CE) es una complicación grave y provoca de forma excepcional obstrucción intestinal aguda en su presentación. CASO CLÍNICO: Paciente masculino de 64 años, tratado previamente por gastroenterología por enfermedad de Crohn. Muestra buena respuesta inicial al tratamiento farmacológico por seis semanas, pero después refiere dolor y síntomas no explicados por la colonoscopia. Se realizó CE, con aparición a las 48 horas de cuadro de obstrucción intestinal, signos de respuesta inflamatoria sistémica e irritación peritoneal. Se practicó laparotomía exploradora más resección intestinal con anastomosis laterolateral mecánica y el informe de histopatología confirmó obstrucción de la luz intestinal por CE impactada en la zona de estenosis del íleon terminal. En el postoperatorio inmediato la evolución es buena. A las ocho semanas del procedimiento acude por fístula enterocutánea que tuvo buena respuesta al tratamiento conservador. CONCLUSIÓN: La tasa de retención de CE en la enfermedad de Crohn es de 5 a 6%; antes de programarla se recomienda realizar estudios de imagen para evaluar la permeabilidad de la luz intestinal, si bien los estudios negativos no excluyen la presencia de estenosis. En los casos en que esté indicada la resección intestinal, se recomienda que ésta sea amplia con anastomosis laterolateral mecánica para reducir el riesgo de recurrencia de la enfermedad.

[Utilidad de la proteína C reactiva en el diagnóstico oportuno de fuga de anastomosis en cirugía colorrectal]. / Utility of C-reactive protein in the early diagnosis of anastomotic leakage in colorectal surgery.

INTRODUCCIÓN: La fuga de anastomosis (FA) en cirugía colorrectal es una complicación temida por el incremento de la morbimortalidad. La tasa de FA se reporta desde el 1 hasta el 25%. Realizar el diagnóstico de forma temprana es difícil. OBJETIVO: Determinar el rendimiento diagnóstico de la proteína C reactiva (PCR) en una cohorte de pacientes sometidos a cirugía colorrectal electiva con anastomosis. MÉTODO: Se realizó un estudio prospectivo, comparativo, en 138 pacientes sometidos a cirugía colorrectal con anastomosis de forma electiva, analizando los valores séricos de la PCR los días 1, 3, 5 y 7 del posoperatorio, así como los de leucocitos y otros datos de sepsis abdominal. RESULTADOS: La tasa de FA fue del 6.5%, y los valores de la PCR fueron significativamente más altos en el grupo de pacientes con FA en el tercer día del posoperatorio. Con un punto de corte de 18.5 mg/dl en el tercer día del posoperatorio se obtuvo una sensibilidad del 81%, una especificidad del 91%, un valor predictivo positivo del 45% y un valor predictivo negativo del 98%. CONCLUSIÓN: La medición de la PCR en el tercer día del posoperatorio en pacientes sometidos a cirugía colorrectal electiva con anastomosis primaria o secundaria permite identificar las complicaciones sépticas, incluida la FA. INTRODUCTION: The anastomotic leakage (AL) in colorectal surgery is a complication feared by the increase in morbidity and mortality. The rate of AF is reported from 1 to 25%. Making the diagnosis early is difficult. OBJECTIVE: To determine the diagnostic performance of the C reactive protein (CRP) in a cohort of patients undergoing elective colorectal surgery with anastomosis. METHOD: A prospective, comparative study was conducted in 138 patients undergoing elective anastomosis with colorectal surgery, analyzing the serum values of CRP on postoperative days 1, 3, 5 and 7, as well as leukocytes and other abdominal sepsis data. RESULTS: The AL rate was 6.5%, the CRP values were significantly higher in the group of patients with AF on the 3rd postoperative day; with a cut-off point of 18.5 mg/dl on the third postoperative day, it obtained sensitivity 81%, specificity 91%, positive predictive value 45%, negative predictive value 98%. CONCLUSION: Measurement of CRP on the third postoperative day in patients undergoing elective colorectal surgery with primary or secondary anastomosis allows the identification of septic complications including leakage of anastomosis.

Synchronization of Clocks Through 12 km of Strongly Turbulent Air Over a City.

We demonstrate real-time, femtosecond-level clock synchronization across a low-lying, strongly turbulent, 12-km horizontal air path by optical two-way time transfer. For this long horizontal free-space path, the integrated turbulence extends well into the strong turbulence regime corresponding to multiple scattering with a Rytov variance up to 7 and with the number of signal interruptions exceeding 100 per second. Nevertheless, optical two-way time transfer is used to synchronize a remote clock to a master clock with femtosecond-level agreement and with a relative time deviation dropping as low as a few hundred attoseconds. Synchronization is shown for a remote clock based on either an optical or microwave oscillator and using either tip-tilt or adaptive-optics free-space optical terminals. The performance is unaltered from optical two-way time transfer in weak turbulence across short links. These results confirm that the two-way reciprocity of the free-space time-of-flight is maintained both under strong turbulence and with the use of adaptive optics. The demonstrated robustness of optical two-way time transfer against strong turbulence and its compatibility with adaptive optics is encouraging for future femtosecond clock synchronization over very long distance ground-to-air free-space paths.

Field test of a distributed fiber-optic intrusion sensor system for long perimeters.

Field tests in desert terrain of a distributed sensor system for detecting and locating intruders based on the phase-sensitive optical-time-domain reflectometer (phi-OTDR) are described. The sensing element is a single-mode telecommunications fiber in a 4.5 mm diameter cable buried in a trench filled with loose sand. Light pulses from a continuous-wave Er:fiber Fabry-Perot laser with a narrow (<3 kHz) instantaneous linewidth and low (few kilohertz per second) frequency drift are injected into one end of the fiber, and the orthogonal polarizations of the backscattered light are monitored with separate receivers. Localized phase changes in the optical carrier are sensed by subtracting a phi-OTDR trace from an earlier stored trace. High sensitivity and consistent detection of intruders on foot and of vehicles traveling down a road near the cable line was realized over a cable length of 8.5 km and a total fiber path of 19 km in real time.

Polarization discrimination in a phase-sensitive optical time-domain reflectometer intrusion-sensor system.

A distributed sensor system for detecting and locating intruders based on a phase-sensitive optical time-domain reflectometer (phi-OTDR) that utilizes polarization discrimination is described. The sensing element is a single-mode telecommunications fiber in a 3 mm diameter cable buried along a monitored perimeter in a 20-46 cm deep, 10 cm wide trench in clay soil. Light pulses from a continuous-wave Er fiber Fabry-Perot laser with a narrow (< 3 kHz) instantaneous linewidth and low (a few Kilohertz per second) frequency drift are injected into one end of the fiber, and the orthogonal polarizations of the backscattered light are monitored with separate receivers. Localized phase changes in the optical carrier are sensed by subtraction of a phi-OTDR trace from an earlier stored trace. In field tests with a monitored length of 12 km, detection of intruders on foot as far as 4.5 m from the cable line was consistently achieved.

Digital and analog readout systems for fiber-optic strain sensors as applied to the monitoring of roller element bearing systems.

A rotating machinery test rig was instrumented with fiber Fabry-Perot interferometer strain sensors for condition monitoring of rolling element bearings. Strain variations produced by ball passes were observed and analyzed in the time and frequency domain. Wavelength division multiplexing was utilized to simultaneously monitor the sensors with analog and digital readout systems--analog for high bandwidth and digital for high dynamic range and the monitoring of multiple sensors. The effects of imbalance on the shaft, changes in rotational speed, effects on the rotor system, and detection of bearing defects were investigated. Frequency peaks observed in the bearing sensor spectra closely matched predicted values. Imbalance and rotational speed tests showed good agreement with expected trends, and bearing defects were successfully detected.