Optical coherence tomography (OCT) has developed rapidly since its first realisation in medicine and is currently an emerging technology in the diagnosis of skin disease. OCT is an interferometric technique that detects reflected and backscattered light from tissue and is often described as the optical analogue to ultrasound. The inherent safety of the technology allows for in vivo use of OCT in patients. The main strength of OCT is the depth resolution. In dermatology, most OCT research has turned on non-melanoma skin cancer (NMSC) and non-invasive monitoring of morphological changes in a number of skin diseases based on pattern recognition, and studies have found good agreement between OCT images and histopathological architecture. OCT has shown high accuracy in distinguishing lesions from normal skin, which is of great importance in identifying tumour borders or residual neoplastic tissue after therapy. The OCT images provide an advantageous combination of resolution and penetration depth, but specific studies of diagnostic sensitivity and specificity in dermatology are sparse. In order to improve OCT image quality and expand the potential of OCT, technical developments are necessary. It is suggested that the technology will be of particular interest to the routine follow-up of patients undergoing non-invasive therapy of malignant or premalignant keratinocyte tumours. It is speculated that the continued technological development can propel the method to a greater level of dermatological use.

https://link.springer.com/content/pdf/bfm%3A978-3-319-06419-2%2F1.pdf

Optical Coherence Tomography

Electrical energy storage technologies for stationary applications are reviewed. Particular attention is paid to pumped hydroelectric storage, compressed air energy storage, battery, flow battery, fuel cell, solar fuel, superconducting magnetic energy storage, flywheel, capacitor/supercapacitor, and thermal energy storage. Comparison is made among these technologies in terms of technical characteristics, applications and deployment status.

http://promexico.me/Rubenius/WhitePapers/sdarticle%20(1).pdf

Progress in electrical energy storage system: A critical review

When a picosecond light pulse is incident on biological tissue, the temporal characteristics of the light backscattered from, or transmitted through, the sample carry information about the optical absorption and scattering coefficients of the tissue. We develop a simple model, based on the diffusion approximation to radiative transfer theory, which yields analytic expressions for the pulse shape in terms of the interaction coefficients of a homogeneous slab. The model predictions are in good agreement with the results of preliminary in vivo experiments and Monte Carlo simulations.

Time resolved reflectance and transmittance for the non-invasive measurement of tissue optical properties.

Quantitation of near infrared spectroscopic data in a scattering medium such as tissue requires knowledge of the optical pathlength in the medium. This can now be estimated directly from the time of flight of picosecond length light pulses. Monte Carlo modelling of light pulses in tissue has shown that the mean value of the time dispersed light pulse correlates with the pathlength used in quantitative spectroscopic calculations. This result has been verified in a phantom material. Time of flight measurements of pathlength across the rat head give a pathlength of 5.3+or-0.3 times the head diameter.

http://iopscience.iop.org/article/10.1088/0031-9155/33/12/008/pdf

Estimation of optical pathlength through tissue from direct time of flight measurement

Psychophysics of reading XX. Linking letter recognition to reading speed in central and peripheral vision

A new method for accelerating projectiles from velocities of ~0.7 km/s up to -12 km/s using chemical energy is presented in this paper. The concept, called the "ram accelerator," is based on gasdynamic principles similar to those of an airbreathing ramjet but operates in a different manner. The projectile, which resembles the center body of a ramjet, travels through a tube filled with a premixed gaseous fuel and oxidizer mixture. The tube becomes the outer cowling of the ramjet, and the energy release process travels with the projectile. By tailoring the propellant mixture along the tube, a nearly constant acceleration can be achieved. In principle, the ram accelerator can be scaled for projectile masses ranging from grams to hundreds of kilograms and is capable of ballistic efficiencies as high as 30%. A straightforwar d, quasisteady, one-dimensional approach is used to model the acceleration process. The experimental facility developed to investigate the concept is described, and the results of recent experiments are presented. The velocity range of 690-1500 m/s has been explored in a 4.88-m long, 38-mm bore accelerator tube. Using methane, oxygen, and various diluents, accelerations of up to 16,000 g have been achieved with 75 gm projectiles and gas fill pressures of 20 atm. Proof of concept has been demonstrated, and agreement between theory and experiment has been found to be very good.

Ram accelerator - A new chemical method for accelerating projectilesto ultrahigh velocities

Operational characteristics of the thermally choked ram accelerator, a ramjet-in-tube device for accelerating projectiles to ultrahigh velocities, are investigated theoretically and experimentally. The projectile resembles the centerbody of a conventional ramjet and travels through a stationary tube filled with premixed gaseous fuel and oxidizer at high pressure. The combustion process travels with the projectile, its thermal choking producing a pressure field which results in thrust on the projectile. The results of experiments with 45-75 gm projectiles in a 12.2 m long, 38 mm bore accelerator, using methane-based propellant mixtures, are presented in the velocity range of 1150-2350 m/s. Acceleration of projectiles with staged propellants and transitions between different mixtures are investigated and the velocity limits in several propellant mixtures are explored. Agreement between theory and experiment is found to be very good.

Operational characteristics of the thermally choked ram accelerator

Experimental investigations on the propulsive modes of the ram accelerator are reviewed in this paper. The ram accelerator is a ramjet-in-tube projectile accelerator whose principle of operation is similar to that of a supersonic air-breathing ramjet. The projectile resembles the centerbody of a ramjet and travels through a stationary tube filled with a premixed gaseous fuel and oxidizer mixture. The combustion process travels with the projectile, generating a pressure distribution which produces forward thrust on the projectile. Several modes of ram accelerator operation are possible which are distinguished by their operating velocity range and the manner in which the combustion process is initiated and stabilized. Propulsive cycles utilizing subsonic, thermally choked combustion theoretically allow projectiles to be accelerated to the Chapman-Jouguet(C-J) detonation speed of a gaseous propellant mixture. In the superdetonative velocity range, the projectile is accelerated while always traveling faster than the C-J speed, and in the transdetonative regime (85–115 % of C-J speed) the projectile makes a smooth transition from a subdetonative to a superdetonative propulsive mode. This paper examines operation in these three regimes of flow using methane and ethylene based propellant mixtures in a 16 m long, 38 mm bore ram accelerator using 45–90 g projectiles at velocities up to 2500 m/s.

Experimental investigation of ram accelerator propulsion modes

A numerical scheme for calculating hypersonic flows involving shock-induced combustion is discussed. The analysis is limited to inviscid flow and includes chemical nonequilibrium and real-gas effects. Two types of flows are considered. First, the hypersonic, exothermic blunt-body flow problem is examined for mixtures of Hi/Oi and Hi/air, and the numerical results are compared with experimental results. Second, a hypervelocity mass launcher concept known as the "ram accelerator" is investigated in the velocity range of 5-7 km/s. Temperature contours and the distribution of various physical quantities along the ram accelerator projectile surface and tube wall are presented for a 14-deg nose projectile and for a gas mixture of 2Hi + Oi + 5He. In the present study, a new numerical scheme developed for calculating hypersonic chemically reacting flows is described. The new numerical formulation represents a departure from previous computational fluid dynamics models of the ram ac- celerator.11'12 The earlier models were based on a global Arrhe- nius rate equation, with the Arrhenius constants determined from experimental ignition delay studies. The current model is more accurate in that it accounts for the reaction kinetics of a 7 species 8 reaction combustion model. Nonetheless, the ear- lier results were encouraging in that they predicted hyperveloc- ity operation was possible. The new scheme, based on an algorithm developed by Yee and Shinn,13 was applied to spheres moving through mixtures of H 2/O2 and H2/air at speeds above and below the corre- sponding Chapman-Jouguet detonation speed. The results were then compared with the experiments just mentioned. The code was also used to investigate the flow and combustion processes in the ram accelerator, in the velocity range of 5-7 km/s. The first section of this paper presents an overview of the phenomena associated with hypersonic exothermic blunt-body flow. The following sections describe the governing equations, combustion model, and the numerical scheme used. Finally, results are presented for hypersonic blunt-body flows and for a complete ram accelerator configuration. Regimes of Exothermic Blunt-Body Flow Figure 2 shows the structure of the shock layer in the vicinity of the stagnation point of a blunt body moving through a detonable gas mixture. At flight speeds t/i, sufficiently low such that the temperature behind the bow shock is less than the ignition temperature, no combustion will occur. At higher flight speeds, but still below the detonation speed D of the gas mixture, the shock and combustion front are separated by an induction zone of thickness A/. This situation is shown in Fig. 3, obtained from the work of Lehr, 10 for a stoichiometric

Numerical simulation of hypervelocity projectiles in detonable gases

An energy storage and conversion system utilizes unique heat exchange media for storing and transferring heat In one embodiment, a refractory material is heated to the molten state by a solar furnace The refractory material is stored in its molten form and metered to a direct-contact heat exchanger It is fed into the heat exchanger in a plurality of streams that break into a plurality of droplets The droplets flow through the heat exchanger in countercurrent relationship with a relatively inert gas such as argon or nitrogen The gas is heated and expanded through an expansion engine to convert the thermal energy to mechanical energy which in turn can be utilized to produce electricity, for example The refractory can be sufficiently cooled in the heat exchanger to fuse into beads, which can be easily recycled to the solar furnace

Adam P. Bruckner

Papers

Ram accelerator - A new chemical method for accelerating projectilesto ultrahigh velocities

Operational characteristics of the thermally choked ram accelerator

Experimental investigation of ram accelerator propulsion modes

Numerical simulation of hypervelocity projectiles in detonable gases

Heat transfer and storage system