The diffraction of light by sound waves of high frequency. Part II

The theory of the diffraction of light by sound waves of high frequency developed in our earlier paper is extended to the case when the light beam is incident at an angle to the sound wave-fronts, both from a geometrical point of view and an analytical one. It is found that the maxima of intensity of the diffracted light occur in directions which make definite angles, denoted by θ, with the direction of the incident light given by sin(θ+Φ) - sin Φ = ±[(nλ)/(λ∗ )], n (an integer) ≥ 0 where λ and λ∗ are the wave-lengths of the incident light and the sound waves in the medium. The relative intensity of the mth order to the nth order is given by Jm2( ν0 secΦ[(sint)/t] ) / Jn2 ( ν0 secΦ[(sint)/(t)]) where ν0=2πμL /λ,t=πL tanΦ/λ∗, Φ is the inclination of the incident beam of light to the sound waves, μ is the maximum variation of the refractive index in the medium when the sound waves are present and L secΦ is the distance of the light path in the medium. These results explain the variations of the intensity among the various orders noticed by Debye and Sears for variations of Φ in a very gratifying manner

The two types of X-ray reflection in crystals

The new type of X-ray reflection forming the subject of this paper was first described and an explanation of it on the basis of the quantum theory given in a series of papers published earlier this year by Raman and Nilakantan in these Proceedings and elsewhere. The present report is intended to be a self-contained theoretical exposition of the subject and incorporates the ideas already expounded in the papers by Raman and Nilakantan, as also the fuller mathematical treatment by Raman and Nath published in these Proceedings for July 1940. Recent experiments by Nilakantan with diamond completely establish the quantum theoretical explanation of the phenomenon

The diffraction of light by high frequency sound waves. Part III. Doppler effect and coherence phenomena

The theory developed in part I of this series of papers has been developed in this paper to find the Doppler effects in the diffraction components of light produced by the passage of light through a medium containing (1) a progressive supersonic wave and (2) a standing supersonic wave. (1) In the case of the former the theory shows that the nth order which is inclined at an angle sin-1 (-nλ/λ∗) to the direction of the propagation of the incident light has the frequency ν-nν∗ where ν is the frequency of light, ν∗ is the frequency of sound and n is a positive or negative integer and that the nth order has the relative intensity J2n(2πμL/λ) where μ is the maximum variation of the refractive index, L is the distance between the faces of the cell of incidence and emergence and λ is the wavelength of light. (2) In the case of a standing supersonic wave; the diffraction orders could be classed into two groups, one containing the even orders and the other odd orders; any even order, say 2n, contains radiations with frequencies ν±2rν∗ where r is an integer including zero, the relative intensity of the ν±2rν∗ sub-component being J2n-r(πμL/λ) J2n+r(πμL/λ); and odd order, say 2n+1, contains radiations with frequencies ν ± 2r+1̅ν∗, the relative intensity of the ν ± 2r+1̅ν∗ sub-component being J2n-r , (πμL/λ) J2n+r+1(πμL/λ). These results satisfactorily interpret the recent results of Bar that any two odd orders or even ones partly cohere while an odd one and an even one are incoherent

Vitamin D deficiency may exacerbate or prolong arthritis in Chikungunya fever

Background: Chikungunya is a self-limiting acute febrile illness with acute arthritis. It is carried by Aedes aegypti and Aedes albopictus. The disease mainly affected Africa and Asia, though sporadic cases occurred in the other regions of the world. Background: During an outbreak of this illness in India in 2015 we observed that a portion of the patients were suffering from prolonged arthritis. While investigating for the cause of prolonged arthritis we found that most of them were deficient in Vitamin D. Hence we carried up this study of Vitamin D deficiency in Chikungunya patients.Methods: All the probable cases of Chikungunya that attended our hospital between 20th July 2015 to 30th January 2016 were registered for study. Their symptoms and clinical signs were analyzed. All were investigated for hematological abnormalities and excluded for dengue fever by serological testing. Those who were hospitalized with severe arthritis were tested for vitamin D deficiency on the day of admission and those who had arthritis beyond a month on 30th day. Those who had a vitamin D deficiency were treated with supplementation and followed up for another three months.Results: Symptoms were analyzed and charted. Tenderness of the skin of the legs just above the ankle was found in 38% of patients which was not documented in the earlier study. 86% of patients had elevated C-reactive protein average being 21 mg/l. 90% 0f patients admitted to the hospital had Vitamin D deficiency and 62% of patients who had arthritis beyond one month had Vitamin D levels less than 20 ng/ml. Correction of vitamin D deficiency alleviated their pain early.Conclusions: Testing for Vitamin D deficiency in all the patients of Chikungunya admitted to the hospital and those suffering from joint pains beyond one month and treating with Vitamin D supplementation, may be prudent to alleviate the suffering of Chikungunya

Honeycomb Core Permeability Under Mechanical Loads

A method for characterizing the air permeability of sandwich core materials as a function of applied shear stress was developed. The core material for the test specimens was either Hexcel HRP-3/16-8.0 and or DuPont Korex-1/8-4.5 and was nominally one-half inch thick and six inches square. The facesheets where made of Hercules' AS4/8552 graphite/epoxy (Gr/Ep) composites and were nominally 0.059-in. thick. Cytec's Metalbond 1515-3M epoxy film adhesive was used for co-curing the facesheets to the core. The permeability of the specimens during both static (tension) and dynamic (reversed and non-reversed) shear loads were measured. The permeability was measured as the rate of air flow through the core from a circular 1-in2 area of the core exposed to an air pressure of 10.0 psig. In both the static and dynamic testing, the Korex core experienced sudden increases in core permeability corresponding to a core catastrophic failure, while the URP core experienced a gradual increase in the permeability prior to core failure. The Korex core failed at lower loads than the HRP core both in the transverse and ribbon directions

A new technique for laser cooling with superradiance

We present a new theoretical scheme for laser cooling of rare earth doped solids with optical super-radiance (SR), which is the coherent, sharply directed spontaneous emission of photons by a system of laser excited rare earth ions in the solid state host (glass or crystal). We consider an Yb3+ doped ZBLAN sample pumped at the wavelength 1015 nm with a rectangular pulsed source with a power of ~433W and duration of 10ns. The intensity of the SR is proportional to the square of the number of excited ions. This unique feature of SR permits a dramatic increase in the rate of the cooling process in comparison with the traditional laser cooling of the rare earth doped solids with anti-Stokes spontaneous incoherent radiation (fluorescence). This scheme overcomes the limitation of using only low phonon energy hosts for laser cooling.Comment: 10 pages,6 figure