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ObjectivesCOVIDTrach is a UK multicentre prospective cohort study project that aims to evaluate the outcomes of tracheostomy in patients with COVID-19 receiving mechanical ventilation and record the incidence of SARS-CoV-2 infection among healthcare workers involved in the procedure.DesignData on patient demographic, clinical history and outcomes were entered prospectively and updated over time via an online database (REDCap). Clinical variables were compared with outcomes, with logistic regression used to develop a model for mortality. Participants recorded whether any operators tested positive for SARS-CoV-2 within 2 weeks of the procedure.SettingUK National Health Service departments involved in treating patients with COVID-19 receiving mechanical ventilation.ParticipantsThe cohort comprised 1605 tracheostomy cases from 126 UK hospitals collected between 6 April and 26 August 2020.Main outcome measuresMortality following tracheostomy, successful wean from mechanical ventilation and length of time from tracheostomy to wean, discharge from hospital, complications from tracheostomy, reported SARS-CoV-2 infection among operators.ResultsThe median time from intubation to tracheostomy was 15 days (IQR 11, 21). 285 (18%) patients died following the procedure. 1229 (93%) of the survivors had been successfully weaned from mechanical ventilation at censoring and 1049 (81%) had been discharged from hospital. Age, inspired oxygen concentration, positive end-expiratory pressure setting, fever, number of days of ventilation before tracheostomy, C reactive protein and the use of anticoagulation and inotropic support independently predicted mortality. Six reports were received of operators testing positive for SARS-CoV-2 within 2 weeks of the procedure.ConclusionsTracheostomy appears to be safe in mechanically ventilated patients with COVID-19 and to operators performing the procedure and we identified clinical parameters that are predictive of mortality.Trial registration numberThe study is registered with ClinicalTrials.Gov (NCT04572438).

Background Cohorts of severely ill patients with COVID-19 have been described in several countries around the globe, but to date there have been few published reports from the United Kingdom (UK). Understanding the characteristics of the affected population admitted to intensive care units (ICUs) in the UK is crucial to inform clinical decision making, research and planning for future waves of infection. Methods We conducted a prospective observational cohort study of all patients with COVID-19 admitted to a large UK ICU from March to May 2020 with follow-up to June 2020. Data were collected from health records using a standardised template. We used multivariable logistic regression to analyse the factors associated with ICU survival. Results Of the 156 patients included, 112 (72%) were male, 89 (57%) were overweight or obese, 68 (44%) were from ethnic minorities, and 89 (57%) were aged over 60 years of age. 136 (87%) received mechanical ventilation, 77 (57% of those intubated) were placed in the prone position and 95 (70% of those intubated) received neuromuscular blockade. 154 (99%) patients required cardiovascular support and 44 (28%) required renal replacement therapy. Of the 130 patients with completed ICU episodes, 38 (29%) died and 92 (71%) were discharged alive from ICU. In multivariable models, age (OR 1.13 [95% CI 1.07–1.21]), obesity (OR 3.06 [95% CI 1.16–8.74]), lowest P/F ratio on the first day of admission (OR 0.82 [95% CI 0.67–0.98]) and PaCO2 (OR 1.52 [95% CI 1.01–2.39]) were independently associated with ICU death. Conclusions Age, obesity and severity of respiratory failure were key determinants of survival in this cohort. Multiorgan failure was prevalent. These findings are important for guiding future research and should be taken into consideration during future healthcare planning in the UK.

Background: Precision medicine approaches targeting patients based on disease subtype have transformed approaches to cancer, asthma, and other heterogeneous syndromes. Two distinct subphenotypes of ARDS have been identified in three US-based clinical trials and respond differently to positive end-expiratory pressure and fluid management. It remains unknown if these subphenotypes exist in different populations and respond differently to pharmacotherapies. Methods: We conducted a secondary analysis using data from 539 patients enrolled in a UK multicenter, placebo-controlled randomized trial of simvastatin for ARDS (HARP-2). Latent class analysis was applied to baseline data without consideration of outcomes to identify subphenotypes. Clinical outcomes were compared across subphenotypes and treatment groups. Findings: A two class (two-subphenotype) model was an improvement over a one class model (pInterpretation: Two subphenotypes of ARDS were identified in the HARP-2 cohort, withdistinct clinical and biological features and disparate clinical outcomes; the hyper-inflammatory subphenotype had improved survival with simvastatin compared to placebo. These findings support further pursuit of predictive enrichment strategies in critical care clinical trials.

In time critical power up applications, such as pre-launch preparation of smart munitions, both power and guidance information needs to be transferred rapidly from the host to the munitions. Tethered solutions are not practical and the existing magnetic inductive charging methods are slow and have limited data transfer rate capability. A wireless solution based on the use of high power laser diodes is presented. Custom dual-junction photo-voltaic cells achieve power conversion efficiencies exceeding 50% at a single wavelength of operation. Energy transfer times of 3.5 s have been achieved for energy levels of 90 J. Guidance and other control data is uploaded to on-board memory devices at a rate of 500 kb/s, through the use of an additional photodiode, which can receive a small fraction of the modulated power beam. A removable collar provides an alignment free charging/data solution enabling rapid deployment of multiple munitions.

The process of harvesting mechanical energy from the environment and converting it to usable electrical energy can be illustrated as shown in the block diagram of Fig. 2.1. The input mechanical energy to be converted to electrical energy may be in the form of potential energy and/or kinetic energy. The mechanical system providing the mechanical energy for harvesting is hereinafter referred to as the “host system.” The host system may be capable of providing mechanical energy in a number of ways, for example, through linear or rotatory vibration of its structure; through a rocking motion such as experienced in a boat, ship, or buoy; through random relative motion between relatively rigid machine components, such as the motion between different links of a car suspension system; or through shock loading experienced by a weapon platform during firing or target impact. In many cases, and depending on the mechanical-to-electrical energy transducer (electrical generator) being employed, an interfacing mechanism is needed for effective transfer of mechanical energy to the energy-harvesting device. Such interfacing mechanisms may, for example, be needed to amplify force or motion, vary the input force or motion frequency, convert a shock loading impulse to oscillatory or vibratory motion, etc. The interfacing mechanism may perform more than one function depending on the application, the host system, and the transducer characteristics. For example, in many cases, the interfacing mechanism is desired to maximize the rate or amount of mechanical energy transferred to the transducer. In other cases, this mechanism is used to “condition” the available mechanical energy to make the energy transfer possible while protecting the transducer and/or the host system. An interfacing mechanism may connect the structure or a component of the host system directly to the energy-conversion transducer or indirectly via certain intermediate elements such as vibrating structures or magnetic coupling elements.

Harvesting electrical energy from mechanical energy of a mechanical (host) system involves the use of transducers (electrical generators) such as those introduced in Chapter 2. In almost all cases an appropriate interfacing (“conditioning”) mechanism is needed for effective integration of the transducer with the source of mechanical energy, i.e., the host system. Such interfacing or conditioning mechanisms may for example be needed to amplify force or displacement or to increase or decrease input displacement or frequency of an input oscillatory motion. Hereinafter, the term interfacing mechanism is intended to refer to those devices that are used to transfer mechanical energy to the transducer, while in some cases performing certain motion and/or force conditioning action. In addition, motion is intended to refer to translational as well as rotational motions. The term “force” is used to also indicate couple, moment, and torque when appropriate. The transfer of mechanical energy to a transducer may be direct or through other intermediate elements in which the mechanical energy may, for example, be stored in the form of potential or kinetic energy and when needed (or a threshold is reached) be released to the transducer for conversion to electrical energy.

The shape optimization of composite flexbeam sections of a bearingless helicopter rotor is studied using a finite element (FE) sectional analysis integrated with an efficient evolutionary optimization algorithm called particle swarm assisted genetic algorithm (PSGA). The sectional optimization framework is developed by automating the processes for geometry and mesh generation, and the sectional analysis to compute the elastic and inertial properties. Several section shapes are explored, modeled using quadratic B-splines with control points as design variables, through a multiobjective design optimization aiming minimum torsional stiffness, lag bending stiffness, and sectional mass while maximizing the critical strength ratio. The constraints are imposed on the mass, stiffnesses, and critical strength ratio corresponding to multiple design load cases. The optimal results reveal a simpler and better feasible section with double-H shape compared to the triple-H shape of the baseline where reductions of 9.46%, 67.44% and 30% each are reported in torsional stiffness, lag bending stiffness, and sectional mass, respectively, with critical strength ratio greater than 1.5.

High contrast imaging, in the presence of a bright background, is a challenging problem encountered in diverse applications ranging from the daily chore of driving into a sun-drenched scene to in vivo use of biomedical imaging in various types of keyhole surgeries. Imaging in the presence of bright sources saturates the vision system, resulting in loss of scene fidelity, corresponding to low image contrast and reduced resolution. The problem is exacerbated in retro-reflective imaging systems where the light sources illuminating the object are unavoidably strong, typically masking the object features. This manuscript presents a novel theoretical framework, based on nonlinear analysis and adaptive focal plane transmittance, to selectively remove object domain sources of background light from the image plane, resulting in local and global increases in image contrast. The background signal can either be of a global specular nature, giving rise to parallel illumination from the entire object surface or can be represented by a mosaic of randomly orientated, small specular surfaces. The latter is more representative of real world practical imaging systems. Thus, the background signal comprises of groups of oblique rays corresponding to distributions of the mosaic surfaces. Through the imaging system, light from group of like surfaces, converges to a localized spot in the focal plane of the lens and then diverges to cast a localized bright spot in the image plane. Thus, transmittance of a spatial light modulator, positioned in the focal plane, can be adaptively controlled to block a particular source of background light. Consequently, the image plane intensity is entirely due to the object features. Experimental image data is presented to verify the efficacy of the methodology.

Angular orientation of both mobile and stationary objects continues to be an ongoing topic of interest for guidance and control as well as for non-GPS based solutions for geolocations of assets in any environment. Currently available sensors, which include inertia devices such as accelerometers and gyros; magnetometers; surface mounted antennas; radars; GPS; and optical line of sight devices, do not provide an acceptable solution for many applications, particularly for gun-fired munitions and for all-weather and all environment scenarios. A robust onboard full angular orientation sensor solution, based on a scanning polarized reference source and a polarized geometrical cavity orientation sensor, is presented. The full position of the object, in the reference source coordinate system, is determined by combining range data obtained using established time-of-flight techniques, with the angular orientation information.

We consider a two-phase model of melt spinning including flow induced crystallization. Introducing slight modifications in the model we perform numerical simulations on it. We present comparison of our velocity profiles with the experimental profiles provided by the company Freudenberg & Co.

We describe a novel technique for improving the sensitivity of analytical instruments based on the measurement of fluorescent intensity. Independent measurement of the Rayleigh scattered intensity component by means of a second photodetector leads to normalized data, which are independent of various experimental parameters. Incorporation of this technique into a fully automated capillary waveguide biosensor improved the instrument sensitivity by a factor of three. The technique enables quantification, as well as detection, of the hybridized target molecules.

Angular orientation of an object such as a projectile, relative to the earth or another object such as a mobile platform continues to be an ongoing topic of interest for guidance and/or steering. Currently available sensors, which include inertia devices such as accelerometers and gyros; magnetometers; surface mounted antennas; radars; GPS; and optical line of sight devices, do not provide an acceptable on-board solution for many applications, particularly for gun-fired munitions. We present a viable solution, which combines open-aperture sensors with custom designed radiation patterns and one or more amplitude modulated polarization scanning reference sources. Subsequently, the sensor system presents a new approach to angle measurements, with several key advantages over traditional cross-polarization based rotation sensors. Primarily, angular information is coded into a complex spatiotemporal pattern, which is insensitive to power fluctuations caused by environmental factors, while making the angle measurement independent of distance from the referencing source. Triangulation, using multiple sources, may be also used for onboard position measurement. Both measurements are independent of GPS localization; are direct and relative to the established local referencing system; and not subject to drift and/or error accumulation. Results of laboratory tests as well as field tests are presented.

Need exists for untethered transmission of electrical power and data to remote devices and sensors. Several wireless solutions, based on radiation and non-radiation are in existence. Here the focus is on the use of photonic power which is an optimized optical to electrical conversion solution, used for both wireless and guided transportation. High photonic conversion efficiencies of 50% and greater have been demonstrated for wavelength matched laser diodes and photovoltaic cells. However, these existing solutions do not meet the needs of rapid energy transfer to remote devices, such as munition shells prior to launch. We report on the design and fabrication of a 16-cell array of densely packed photonic power converters that can power a munition shell immediately prior to launch. A laser beam delivers power and data to the PPC array. Thermal simulation, using FEA shows that the each of the cells can be operated at an equivalent irradiance of 1000x suns, giving an energy transfer rate of 17.5 J.s -1 for the array. Thus, two 10 F super-capacitors, typically used in munitions, can be charged is under 5 seconds. Further, using the measured capacitance of 2.4 nF for the array, data can be transported to the munition on the laser power beam, at a rate exceeding 5 Mbps.

Micro-capillaries are finding increasing utility in the development of portable analytical sensors. We present design guidelines for optimizing the collection of free propagating fluorescence for capillary waveguide sensors used in the detection of nucleic acids. A dual function integrated opto/fluid connector is also described. Evanescent wave excitation of the coating layer containing a DNA probe is achieved by using a fiber optic ring arrangement for coupling light directly into the capillary wall. The central part of the connector is used for injecting a DNA or RNA target into the capillary channel. In situ hybridization has been used to detect target molecules at a concentration of 30 pg ml −1 . The sensor can be regenerated for repeated detection of DNA or RNA targets.

Cylindrical capillaries can be used as optical elements in a waveguide, where refraction will confine an appropriately focused light beam to pass through the interiors of successive capillaries in a flat parallel array. Such a capillary waveguide allows efficient illumination of samples in multiple capillaries with relatively little laser power. Analytical expressions derived under paraxial and thin-lens approximations provide guidance in selecting the capillary sizes and the refractive indices that will produce the waveguiding effect, but accurate predictions require exact ray tracing. Small reflective losses as the light passes through the capillary surfaces cause cumulative intensity decreases, but the resulting lack of uniformity can be compensated to a considerable extent by illuminating the capillary array from both sides. A 12-capillary waveguide illuminated from both sides in air has a difference of less than 10% from the strongest to the weakest illumination. By increasing the refractive index of both the external medium and the contents of the capillaries, a 96-capillary waveguide for DNA sequencing could be produced that would also provide nearly uniform illumination. A 12-capillary, bi-directionally illuminated waveguide system for DNA sequencing has been constructed. The two focused laser beams are delivered by integrated fiber optic transmitters (IFOTs), and fluorescence is collected by a set of optical fibers whose spacing exactly matches that of the capillaries in the waveguide. The system is easy to align and provides sensitive detection of fluorescence with minimal cross-talk between channels.

A high-pressure fiber-optic light-scattering spectrometer has been constructed for in situ observation of molecular dissolution/association as well as the polymerization process in supercritical fluids. Single (or multiple) fiber-optic probes, each comprised of a single optical fiber (or multiple optical fibers) and a graded index microlens, are used to transmit the incident laser beam and to receive the scattered light as well as the transmitted light from the high pressure cell. The direct immersion in the scattering medium of the fiber-optic probes makes the spectrometer more compact and more flexible with an easier alignment process. With the miniaturization and flexibility, our high-pressure light-scattering cell can be transported and adapted in combination with other physical techniques, such as synchrotron small angle x-ray scattering which requires a different set of windows (e.g., made of diamond) suitable for x-ray transmissions. This spectrometer has been successfully used for the in situ study of the molecular association behavior of a diblock copolymer of 1,1-dihydroperfluorooctylacrylate and vinyl acetate in supercritical carbon dioxide under pressures up to 552 bar.

A laser scanning system for measurement of the attitude angles of a fixed projectile is described. The angular information extracted from the temporal signal is dependent on the spatially sensitive reflection of the outer surface. Results from a laboratory based laser scanning system, operating over a distance of about 1 m, demonstrate the concept. Azimuth and elevation of a cylindrical projectile are recovered from the temporal signature obtained by scanning a laser spot across a bar pattern painted on its surface. Measurement accuracy and reproducibility are a function of the scan spot size, the contrast of the painted bar pattern and the overall timing accuracy of the composite system. Differential angular accuracy of 1 mrad has been demonstrated using a planar target.

This paper describes the novel use of high power laser diodes for rapid delivery of power and data to wireless sensors when solar illumination is not an option and continuous point-to-point power flow is not desirable. A single high power, laser diode source can service multiple sensors, either sequentially or in parallel. Laser irradiance levels exceeding 10k suns decrease the charging time of a super-capacitor, without damage to the photovoltaic converter. Alternatively, multiple devices, connected in parallel, also reduce the charging time. We demonstrate the efficacy of the approach using four photonic power converters. Simultaneously, with delivery of power, IrDA trans-receivers establish full-duplex communication between the transmitter and receiver.

This paper describes the design, fabrication, and testing of an integrated fiber optic light probe system for monitoring blade tip deflections, vibrational modes, and changes in blade tip clearances in the compressor stage of rotating turbomachinery. The system comprises a set of integrated fiber optic light probes which are positioned to detect the passing blade tip at the leading and the trailing edges. In this configuration measurements of both blade vibrations and steady‐state blade deflection can be obtained from the timing information provided by each light probe, which comprises an integrated fiber optic transmitting channel and a number of high numerical aperture receiving fibers, all mounted in the same cylindrical housing. A spatial resolution of 50 μm is possible with the integrated fiber optic technology, while keeping the outer diameter below 2.5 mm. Additionally, one fiber sensor provides a capability of monitoring changes in the blade tip clearance of the order of 10 μm. Measurements from a single stage compressor facility and an engine‐fan rig in a 9 ft×15 ft subsonic wind tunnel are presented.

A compact backscatter fiber optic system, comprising a semiconductor laser diode, a fiber optic probe and a self-contained photomultiplier, is described. Backscatter fiber optic probes provide easy access over a range of scattering angles between 95 and 175 degrees. Accuracy of the portable dynamic light scattering system is assessed through measurements made on a 39 nm polystyrene latex spheres suspension.

Laser light propagated in semi-transparent turbid media such as biological tissue loses its coherence and polarization. Speckle contrast can be considered as a metric of light coherence. Recently we demonstrated that polychromatic speckle contrast and degree of polarization are useful criteria for skin lesion differentiation. To gain a better understanding of this complex process, we conducted an experiment to measure the speckle contrast and the average degree of polarization of solid skin phantoms with controllable roughness and bulk optical parameters of the order of human skin. The data validated that bulk scattering along with roughness introduce speckle contrast and DOLP reduction. Also we observed that speckle contrast and the average degree of polarization were related to the bulk scattering coefficient. The speckle contrast vs. degree of linear polarization dependence reveals a near linear relationship with the slope varying with the scattering coefficient of the material. The significant difference between slopes for two phantoms with slightly dissimilar optical properties could suggest that this pair of measurements (speckle contrast vs. degree of linear polarization) is highly sensitive to the tissue type and can be potentially used as a parameter for material differentiation.

An integrated fiber-optic probe comprising a short length of multimode fiber that is fusion spliced to a monomode optical fiber has been fabricated for imaging and nonimaging applications. The fiber probe, typically 250 µm in diameter, can deliver a focused Gaussian spot approximately 25 µm in diameter at a distance of approximately 500 µm from the tip. Two off-the-shelf graded-index multimode fibers have been used in the fabrication of imaging and nonimaging probes. These integrated probes have considerably improved the spatial resolution of backscatter lensless fiber probes being utilized in the dynamic light-scattering characterization of colloidal suspension.

An integrated fiber optic probe, comprising a monomode optical fiber fusion spliced to a short length of a graded-index multimode fiber, is fabricated for use as a coherent receiver in dynamic light scattering. The multimode fiber is cleaved to provide a gradient-index fiber lens with a focal length of 125 microns and an f-number close to unity. An integrated fiber receiver is used to measure the intensity-intensity autocorrelation data from a 0.05 percent by weight concentration of an aqueous suspension of polystyrene latex spheres. Analysis of 100 independent data sets indicates that the particle size can be recovered with an accuracy of +/- 1 percent.

This paper demonstrates the utility of a noninvasive backscatter fiber optic probe for dynamic light-scattering characterization of a microemulsion comprising sodium dodecyl sulfate/1-butanol/ brine/heptane. The fiber probe, comprising two optical fibers precisely positioned in a stainless steel body, is a miniaturized and efficient self-beating dynamic light-scattering system. Accuracy of particle size estimation is better than ±2%.

Background: The intermixing of light reflected from tissue surface and scattered from tissue volume complicates skin surface roughness assessment by laser speckle technique, a non-invasive optical method based on the analysis of the contrast of a speckle pattern. Objective: In this study we investigated optical discrimination methods to separate the two contributions in a speckle pattern. Methods: Three discrimination methods, spatial, polarization and spectral filtering, were implemented to suppress light from skin internal volume in a laser speckle device. In order to determine the effectiveness of the discrimination methods, speckle patterns were obtained from healthy volunteers, and polychromatic speckle contrast was computed before and after each filtering procedure. Results: Speckle contrast increased after discrimination filtering. A simple formula was derived to calculate the speckle contrast associated with light scattered from the skin surface. This corrected speckle contrast was proposed to be used for skin roughness assessment.

A fiber‐optic probe employing two monomode optical fibers, one for transmitting a Gaussian laser beam to the scattering volume and the second, positioned at some backscatter angle, for receiving the scattered light is described. Performance and suitability of the system for a process control environment is assessed by studying a suspension of polystyrene latex particles over a wide range of sizes and concentrations. The results show that the probe is ideal for a process control environment in industrial and laboratory applications. Particle size is recovered, without any additional corrections for multiple light scattering, in concentrations containing up to 10% solids of 39‐nm polystyrene latex spheres.

Objective: Prospective studies show a 10% incidence of sternal wound infection (SWI) after 90 days of follow-up, compared with infection rates of 5% reported by the National Nosocomial Infections Surveillance System after only 30 days of follow-up. This incidence increases 2–3 times in high-risk patients. Design: Prospective randomised double-blind controlled clinical trial. Setting: Cardiothoracic centre, UK. Patients: Patients were eligible if they were undergoing median sternotomy for primary isolated coronary artery bypass grafting, with at least one internal thoracic artery used for coronary grafting and having one or more of the following three risk factors: (1) obesity, defined as body mass index 30 kg/m 2 ; (2) diabetes mellitus; or (3) bilateral internal thoracic artery grafts (ie, the use of the other internal thoracic artery). Interventions: The study group received a single dose of gentamicin 2 mg/kg, rifampicin 600 mg and vancomycin 15 mg/kg, with three further doses of 7.5 mg/kg at 12-hour intervals. The control group received cefuroxime 1.5 g at induction and three further doses of 750 mg at 8-hour intervals. Main outcome measures: The primary end point was the incidence of SWI at 90 days. The secondary end point was the antibiotic and hospital costs. Results: During the study period, 486 patients underwent isolated coronary artery bypass grafting with a 30-day SWI of 7.6%. 186 high-risk patients were recruited and analysed: 87 in the study group and 99 in the control group. 90-day SWI was significantly reduced in 8 patients in the study group (9.2%; 95% CI 3.5% to 15.3%) compared with 25 patients in the control group (25.2%; 95% CI 19.5% to 39.4%; p = 0.004). The study group had a significantly lower cost of antibiotics (21.2% reduction—US$96/patient; p Conclusions: Longer and broader-spectrum antibiotic prophylaxis significantly reduces the incidence of SWI in high-risk patients, with a significant economic benefit in costs of antibiotics as well as hospital costs.

Background: Ascending aortic pseudoaneurysms following prior cardiac procedures are a rare entity. We reviewed our institutional experience given the isolated case reports in the literature. Methods: A 10-year retrospective review identified 5 patients who underwent ascending aorta pseudoaneurysm repair. There were 3 women and 2 men with a median age of 70 years (range 63 to 79 years). Median duration from initial CABG to pseudoaneurysm repair was 5 years (range 5 months to 18 years). The clinical presentations included dyspnoea (2 patients), chest pain, fever of unknown origin, and a pulsatile mass. Four patients underwent urgent investigation and surgery. Diagnosis was established via CT scan (3 patients), transesophageal echocardiogram (1 patient), and MRA (1 patient). Two patients had a prior history of sternal wound infection. Results: Mortality was 60%. One survivor experienced a stroke. The etiology was prior cannulation site in 4 cases and vein graft anastamotic site in 1. Necrotic aortic tissue was noticed in 2 cases. Aortic tissue cultures were negative in all the patients. Cardiopulmonary bypass was established prior to sternotomy in 4 cases and 1 case was performed off-pump. Inadvertent rupture of the pseudoaneurysm (without exsanguination) occurred in 2 cases following sternotomy. Repair was performed with bovine pericardial patch in 2 cases and plication in 3 cases. Conclusion: This highlights the varied presentation, necessity for urgent diagnosis and repair with a high operative mortality due to the late presentation. Aggressive diagnosis should be sought and consideration should be given to catheter-based interventions for initial treatment.

A fiber optic laser probe based system is described for real time monitoring of flutter in rotating turbomachinery. The digital flutter monitoring system is designed for continuous processing of blade tip timing data at a rate of 10 MB/s. A USB2.0 interface provides un-interrupted real time processing of the data. The blade tip arrival times are measured with a 50 MHz bscillator and a 24-bit pipelined counter architecture. A graphical user interface provides on-line interrogation of any blade tip from any light probe sensor. Alternatively, data from all blades can be superimposed into a single composite scatter plot displaying the vibration amplitude of each blade. A hardware platform was developed to simulate a seventy two bladed turbine operating at 15,000 rpm. Blade tip responses from three light probes were generated in an infinite loop, providing reproducible and controlled conditions for testing the vibration monitoring system. Time interval measurements were consistently made with a single count error in a 24-bit count vector. Real time testing was done using a two blade rotor mounted in an evacuated chamber at the Spin Rig Facility at the NASA Glen Research Center. The shaft in this facility was suspended by two radial magnetic bearings and the nonsynchronous vibration was communicated to the blades through the magnetic bearing. The shaft motion was much smaller than the blade vibratory amplitude, realistically simulating flutter vibrations. Nonsynchronous vibratory amplitudes for the first mode were of the order of twenty mils and for the second mode of the order of a few mils.Copyright © 2004 by ASME

In this paper a time-of-flight probe system incorporating the two integrated fiber optic probes which are tilted equally relative to the probe holder centerline, is applied for the first time to measure the tip clearance of an advanced fan prototype. Tip clearance is largely independent of the signal amplitude and it relies on timing measurement. This work exposes optical effects associated with the fan blade stagger angle that were absent during the original spin-rig experiment on the zero stagger rotor. Individual blade tip clearances were measured with accuracy of +/- 127-mm (+/- 0.005-in). Probe features are discussed and improvements to the design are suggested.

Currently, the majority of fiber-optic blade instrumentation is being designed and manufactured by aircraft-engine companies for their own use. The most commonly employed probe for optical blade deflection measurements is the spot probe. One of its characteristics is that the incident spot on a blade is not fixed relative to the blade, but changes depending on the blade deformation associated with centrifugal and aerodynamic loading. While there are geometrically more complicated optical probe designs in use by different engine companies, this paper offers an alternate solution derived from a probe-mount design feature that allows one to change the probe axial position until the incident spot contacts either a leading or a trailing edge. By tracing the axial position of either blade edge one is essentially extending the deflection measurement to two dimensions, axial and tangential. The blade deflection measurements were obtained during a wind tunnel test of a fan prototype.

This paper describes two dual-laser probe integrated fiber optic systems for measuring blade tip clearance in rotating turbomachinery. The probes are nearly flush with the casing inner lining resulting in minimal flow disturbance. The two probes are closely spaced in a circumferential plane and are slanted at an angle relative to each other so that the blade tip traverse time of the space between the two laser beams varies with the tip radius allowing determination of the tip clearance at the rotor operating conditions. The tip clearance can be obtained for all the blades in a rotor with a single system, provided there are no synchronous vibrations present at a particular operating condition. These probes were installed in two holders; one provided an included angle between the probes of 20 degrees, and the other provided an included angle of 40 degrees. The two configurations were calibrated in a vacuum spin rig facility that is capable of reproducing realistic blade tip speeds.

A 12-capillary prototype electrophoresis system for DNA sequencing has been constructed. Laser illumination is introduced into an optical waveguide that is formed by an array of individual capillaries that serve both as the optical elements of the periodic array and as the channels containing sieving media for electrophoresis. A theoretical framework and experimental data will be presented to illustrate the viability of this approach.

A compact fiber optic system, utilizing a lensless backscatter fiber optic probe, and a semiconductor laser is used as a non-invasive tool for in vivo characterization of the proteins in the eye lens of several animals. The system exploits the extremely sensitive technique of dynamic light scattering, which uses a laser beam to probe the temporal characteristics of the proteins present in eye lens fluid. The technique, with appropriate electronics and signal processing provides a rapid means of determining the size of the (alpha) -crystallin in the protein-water system. Changes in the size of the protein molecules can be tracked over the age of the eye lens; an abrupt increase in size is associated with the early cataractous formation. This paper describes the fiber optic system and discusses results obtained from measurements made on sedated rabbits, pigs and cats. A clear difference in the size of the (alpha) -crystallin of normal and cataractous lenses is observed.

Design and fabrication of an integrated backscatter fiber optic probe is described in this paper. A short section of a gradient index optical fiber is fusion spliced to two separate monomode optical fibers; the two fibers are mounted into a stainless steel face plate. One fiber is used to transmit either a focussed or collimated laser beam to the scattering region. The second fiber collects and guides the laser light scattered at a predefined scattering angle to a photomultiplier. Subsequent photon correlation and analysis yields size information of the scattering species.

The hardware development of an integrated backscatter fiber optic system for doing dynamic light scattering (DLS) measurements in the constrained microgravity environment of a space shuttle or space station is described. The small size and light-weight system easily fits in a Spacelab Glovebox and ensures maximum safety for the orbiter crew. It offers high precision particle size measurements from dispersions of colloidal particles within seconds. It needs neither onboard optical alignment nor index matching fluid, and it offers sample mixing and shear melting capabilities to study aggregation (flocculation and coagulation) phenomena under both quiescent and controlled agitation conditions. The system can easily be adapted for other microgravity experiments requiring the use of DLS.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A comparative dynamic light scattering study of BSA and lysozyme is presented. A backscatter fiber optic system and a conventional light scattering spectrometer are used to measure the diameter of proteins in the dilute regime, that is, below concentrations of 10 mg/ml. The fiber optic system operating with a power level of 2 mW at a wavelength of 632.8 nm compares favorably with a conventional system operating with a power level of 40 mW at a wavelength of 514.5 nm. Quasi-elastic light scattering measurements taken at several concentrations demonstrate the utility of a backscatter fiber optic probe for sizing of small molecular weight proteins. The fiber probe, comprising two optical fibers, is about 3 mm in diameter and can be positioned either inside or outside the scattering cell.

This paper demonstrates the application of a lensless fiber optic spectrometer (sensor) to study the onset of cataracts. This new miniaturized and rugged fiber optic probe is based upon dynamic light scattering (DLS) principles. It has no moving parts, no apertures, and requires no optical alignment. It is flexible and easy to use. Results are presented for cold-induced cataract in excised bovine eye lenses, and aging effects in excised human eye lenses. The device can be easily incorporated into a slit-lamp apparatus (ophthalmoscope) for complete eye diagnostics.

A multiple fiber-optic particle sizing probe which uses a linear array of 11 optical fibers positioned in the focal plane of a graded index microlens is presented. The probe, a compact optical spectrum analyzer, provides simultaneous filtering of the angular spectrum of an extended quasi-monochromatic source. Active and passive configurations provide accurate measurements of the particle size distributions. The multiple fiber-optic probe together with processing electronics is a particle sizing sensor which yields the size distribution within 1-2 min.

Optical homodyne detection in the backscatter direction is achieved through a pair of collinearly located fibers in a cylindrical probe body. One fiber illuminates the scattering solution while the other fiber provides optical mixing of the backscattered optical field with a local oscillator derived from the Fresnel reflections at the glass interfaces of the sample container. Homodyne detection is possible over a broad range of particle size and sample concentration with a single probe design.

A fiber‐optic light‐scattering spectrometer with simultaneous operation at wavelengths of 488 and 790 nm is described. The spectrometer can perform both static and dynamic light‐scattering measurements, down to a scattering angle of 8°, from dark‐colored solutions of macromolecules.

We process an optical wave front emanating from a monomode optical fiber by fusion splicing several small sections of step-index and graded-index multimode optical fibers. In this way a wave front of an optical wave can be engineered without its leaving the optical fiber. Results for several integrated coherent imaging delivery systems are presented.

A regularized coherent optical processor, exhibiting considerable immunity to phase noise, is designed and used to achieve resolution beyond the diffraction limit. Regularization is achieved by means of a piezoelectric displacement of one of the feedback mirrors. The optical processor is used for real-time object restoration from noisy, diffraction-limited images. A software implementation of the regularized algorithm, for the case of a two-slit object, shows good agreement with the results obtained from the optical processor.

A lensless backscatter fiber optic probe is used to measure the size distribution of protein molecules inside an excised, but intact, human eye lens. The fiber optic probe, about 5 mm in diameter, can be positioned arbitrarily close to the anterior surface of the eye; it is a trans-receiver, which delivers a Gaussian laser beam into a small region inside the lens and provides a coherent detection of the laser light scattered by the protein molecules in the backward direction. Protein sizes determined from the fast and slow diffusion coefficients show good correlation with the age of the lens and cataractogenesis.

Laser light-scattering measurements of the Brownian motion of a colloidal suspension of silica particles, Syton, by means of the Fiber Optic Doppler Anemometer (FODA) were used to determine the mean and standard deviation of the particle size distribution. Measurements over a wide range of concentrations from undiluted Syton to 0.049% Syton solution showed a consistent power spectrum of scattered light amplitude fluctuations. Using a modified Lorentzian model for the power spectrum, a computer least-squares curve fit and a graphical method were used to calculate the mean and standard deviation of particle radius. The results were consistent for all concentrations of Syton, verifying the versatility of the FODA and the accuracy of the modified Lorentzian model. The mean and standard deviation of particle radius in Syton were found to be 46.5 and 20.8 nm, respectively. It was found that clumping in undiluted Syton caused an apparent increase in the mean and standard deviation of the particle size distribution, as compared with all of the other dilutions where clumping did not occur.

A new fiber‐optic light‐scattering spectrometer, which uses fiber‐optic detector probes each comprising of an optical fiber and a graded index microlens is described. The fiber‐optic detectors form an integral part of the scattering cell, which no longer requires transparent windows for the exit (or entrance) light beam. This feature eliminates the need for a goniometer which is one of the most bulky and expensive components of a conventional light‐scattering spectrometer. Thus, the spectrometer, unlike all of its predecessors, has no moving parts. Our fiber‐optic light‐scattering spectrometer can utilize a reaction vessel of whichever shape or composition as the scattering cell for light‐scattering measurements because the fiber‐optic detector probes are directly immersed in the scattering medium. Furthermore, with the miniaturization using the optical fiber/microlens combination, the light‐scattering spectrometer can be held in the palm of one hand and the signals processed by standard optical fiber remote sensing techniques.

The fiber optic Doppler anemometer, FODA, utilizes laser light directed into a communication-type optical fiber to obtain a heterodyne measurement of scattered light from an object or objects near the tip of the fiber. The FODA is applied in this paper to the measurement of the Brownian motion of a colloidal suspension of submicron particles, Syton W-30. By comparison of the power spectrum of scattered light with appropriate mathematical models, it is possible to determine the size distribution of the particles of the colloid. In addition, the concentration of particles in the colloid may be determined from the mean square photocurrent of the FODA. The accuracy of the FODA was assessed by verifying the assumption of heterodyne detection and by determining the noise and signal-to-noise ratio of the instrument. The accuracy of the particle size distribution determination with the FODA was tested by comparing it with that obtained from electron microscope photographs of the particles in Syton. It was found that the laser-scattering size distribution obtained with the FODA is strongly affected by the scattering amplitude of the spherical particles in Syton, since large particles scatter more light than do small ones. A method of obtaining the true particle size distribution, from the laser-scattering size distribution was shown to yield accurate results, within the statistical accuracy of the data.

A photoelectron correlator based on the measurement of the joint probability distribution function in the arrival times of eight stop pulses following a single start pulse is described. This correlator has a measurement interval of 5 μs and delay time resolution of 2.5 ns. With an eight‐stop capability, much higher count rates can be used without fear of distorting the intensity–intensity time correlation function due to saturation. Thus the accumulation time becomes tolerable for acceptable signal‐to‐noise ratios in time correlation function measurements with such a short delay time increment.