scholarly journals The change in lattice spacing at a crystal boundary

1928 ◽  
Vol 121 (787) ◽  
pp. 247-259 ◽  
Keyword(s):  
Surface Layer ◽  
Crystal Lattice ◽  
Lattice Spacing ◽  
Crystal Surface ◽  
Bragg Reflection ◽  
The Other ◽  
X Rays ◽  
Crystal Boundary ◽  
De Broglie Waves ◽  
Is Theory

Some recent experiments of Davisson and Germer on the scattering of electrons by a crystal have drawn attention to the conditions at a crystal boundary. In interpreting their results in terms of de Broglie waves, the authors have to postulate a contraction of the crystal lattice at the surface— in some cases of as much as 30 per cent.f It is, therefore, important that other independent methods should be devised to indicate what change (if any) takes place at a crystal surface. Unfortunately X-rays are unable to help in this respect as several hundred atomic layers are necessary to produce a Bragg reflection pattern ; nor is theory able to provide an answer in the case of metallic crystals such as are used by Davisson and Germer because little is known of the forces which hold a metal together. Certain other cases can, however, be considered theoretically, and these may indicate the order of the effect to be expected in metallic crystals. In this paper we consider the change in spacing at a (100) boundary of a crystal of the NaCl type, this boundary being considered because it is a natural plane of crystal. Two effects are to be anticipated: (1) a change of spacing between planes at the boundary; (ii) a change of spacing between atoms in the surface layer itself. These effects are considered separately and independently. Actually, of course, each affects the other, but this is assumed to be a correction of the second order.

scholarly journals Experiments on the diffraction of cathode rays.—II

1928 ◽  
Vol 119 (783) ◽  
pp. 651-663 ◽  
Keyword(s):  
Thin Film ◽  
Diffraction Pattern ◽  
Discharge Tube ◽  
Photographic Plate ◽  
Wave Length ◽  
The Other ◽  
X Rays ◽  
Spark Gap ◽  
De Broglie Waves ◽  
Considerable Length

§ 1. The following paper is an account of further experiments which have been made on the lines of those described in these ' Proceedings ’ (vol. 117, p. 600), and largely with the same apparatus. A beam of cathode rays passing normally through a very thin film of metal was found to produce a pattern of concentric rings on a photographic plate about 30 cm. away. These could be explained as a diffraction pattern due to the de Broglie waves of the electron, the atoms of the metal crystals being the diffracting system. In the present paper several points of uncertainty are cleared up, and the work extended to other cases. § 2. As mentioned in a note at the end of the previous paper, the discrepancy of 6 per cent, between the values of the crystal constants of aluminium and gold determined by X-rays, and those found by applying the de Broglie theory to the diffraction rings formed by the cathode rays, has now been explained. It was due to an error in the measurement of the energy of the cathode rays, and hence their wave-length. The energy was measured by a spark-gap connected in parallel with the discharge tube. In the earlier measurements a considerable length of leads and a rectifying valve were included with the discharge tube, and it now appears that an appreciable fraction of the potential fall occurred in these. When two spark-gaps were used, one connected as before, and the other directly across the discharge, there was 1-2 mm. difference in the readings. The following table shows the values of P, the voltage; D, the diameter of the ring corresponding to reflection from the (2, 0, 0) plane; and D√P (1 + P e /1200 m 0 c 2 ), which latter quantity should be constant for any one metal on the de Broglie theory (see previous paper, p. 603). The factor in brackets is the relativity correction, and in the experiments in question never differs from unity by more than 3 per cent.

scholarly journals Chemical Abundances of Early Type Stars

1998 ◽  
Vol 188 ◽  
pp. 224-225
Author(s):  
S. Tanaka ◽  
S. Kitamoto ◽  
T. Suzuki ◽  
K. Torii ◽  
M.F. Corcoran ◽  
...  
Keyword(s):  
Surface Layer ◽  
Stellar Wind ◽  
Nuclear Reactions ◽  
X Rays ◽  
Early Type ◽  
Chemical Abundances ◽  
X Ray ◽  
Low Metallicity ◽  
Early Type Stars

X-rays from early-type stars are emitted by the corona or the stellar wind. The materials in the surface layer of early-type stars are not contaminated by nuclear reactions in the stellar inside. Therefore, abundance study of the early-type stars provides us an information of the abundances of the original gas. However, the X-ray observations indicate low-metallicity, which is about 0.3 times of cosmic abundances. This fact raises the problem on the cosmic abundances.

An Explanation of the Removal of Metastability in Some Hydroacid Salts by Water Adsorption

2001 ◽  
Vol 56 (12) ◽  
pp. 869-872
Author(s):  
B. Baranowski ◽  
A. Lundén
Keyword(s):  
Phase Transition ◽  
Surface Layer ◽  
Water Activity ◽  
Induction Time ◽  
Lattice Spacing ◽  
Water Adsorption ◽  
Zeroth Order ◽  
Exponential Functions ◽  
Kinetics Of ◽  
Volume Decrease

Abstract The metastability of some phases of CsHSO4 and RbH2PO4 is due to the volume decrease at an endothermic phase transition which "locks in" the metastability in question. Water adsorption, which removes these metastabilities, probably exerts a "wedge-like" force which expands the lattice spacing in the surface layer, thus facilitating the start of the phase transition. The induction time and the zeroth order kinetics of the transition in RbH2PO4 are exponential functions of the water activity applied.

Matrix-Mineral Relationships-A. Morphologist's Viewpoint

1979 ◽  
Vol 58 (2_suppl) ◽  
pp. 922-929 ◽  
Author(s):  
M.U. Nylen
Keyword(s):  
Organic Material ◽  
Crucial Role ◽  
Crystal Surface ◽  
Organic Matrix ◽  
The Other ◽  
Enamel Matrix ◽  
Initial Cell ◽  
Cell Product ◽  
Ultrastructural Morphology ◽  
The Matrix

The literature on the ultrastructural morphology of the enamel matrix and its relationship to the crystals is reviewed. Two morphological entities of the matrix are discussed: One is the so-called stippled material which may be the initial cell product; the other, variously described as fibrillar, lamellar, tubular or helical, is thought by many to play a crucial role in nucleation and orientation of the crystals. A number of observations, however, suggest that the latter structures form secondarily to the crystals and that in reality they represent organic material adsorbed to the crystal surface and maintained as independent structures upon removal of the mineral. The need for additional studies is stressed including systematic studies of interactions between constituents of the organic matrix and the apatite crystals.

Structural dynamics of PZT thin films at the nanoscale

2005 ◽  
Vol 902 ◽  
Author(s):  
Alexei Grigoriev ◽  
Dal-Hyun Do ◽  
Dong Min Kim ◽  
Chang-Beom Eom ◽  
Bernhard Adams ◽  
...  
Keyword(s):  
Crystal Lattice ◽  
Lattice Distortion ◽  
Piezoelectric Effect ◽  
Polarization Switching ◽  
X Rays ◽  
Time Resolved ◽  
X Ray ◽  
Converse Piezoelectric Effect ◽  
Ferroelectric Capacitors ◽  
Crystal Lattice Distortion

AbstractWhen an electric field is applied to a ferroelectric the crystal lattice spacing changes as a result of the converse piezoelectric effect. Although the piezoelectric effect and polarization switching have been investigated for decades there has been no direct nanosecond-scale visualization of these phenomena in solid crystalline ferroelectrics. Synchrotron x-rays allow the polarization switching and the crystal lattice distortion to be visualized in space and time on scales of hundreds of nanometers and hundreds of picoseconds using ultrafast x-ray microdiffraction. Here we report the polarization switching visualization and polarization domain wall velocities for Pb(Zr0.45Ti0.55)O3 thin film ferroelectric capacitors studied by time-resolved x-ray microdiffraction.

scholarly journals An Assessment of Skeletal Craniofacial Asymmetry in South Indian Population

2012 ◽  
Vol 13 (1) ◽  
pp. 80-84 ◽  
Author(s):  
G Anil Kumar ◽  
Saibel Farishta ◽  
G Baiju ◽  
VK Taneja ◽  
RC Minocha ◽  
...  
Keyword(s):  
College Students ◽  
South India ◽  
Indian Population ◽  
Cranial Base ◽  
The Other ◽  
South Indian Population ◽  
X Rays ◽  
Base Area ◽  
South Indian ◽  
The Face

ABSTRACT The present study was undertaken to assess the skeletal craniofacial asymmetry in South Indian population by a posteroanterior cephalometric radiographic method. The skeletal craniofacial structures on one side of the face were compared with that of the other, by drawing various triangles representing different craniofacial regions. The sample consisted of 60 subjects (30 males and 30 females) aged between 18 to 25 years, who were mainly dental college students from South India. Overall 52 X-rays were obtained, with four errors each in the male and the female groups. The results revealed that the total facial structures in the South Indian population were larger on the left side (statistically insignificant). The cranial base area exhibited a greater degree of asymmetry than any other component area of the face, which might be due to the inaccuracy at the condylar point. How to cite this article Taneja VK, Kumar GA, Farishta S, Minocha RC, Baiju G, Gopal D. An Assessment of Skeletal Craniofacial Asymmetry in South Indian Population. J Contemp Dent Pract 2012;13(1):80-84.

Diamond channel-cut crystals for high-heat-load beam-multiplexing narrow-band X-ray monochromators

2021 ◽  
Vol 28 (6) ◽  
Author(s):  
Yuri Shvyd'ko ◽  
Sergey Terentyev ◽  
Vladimir Blank ◽  
Tomasz Kolodziej
Keyword(s):  
Heat Load ◽  
Narrow Band ◽  
Bragg Reflection ◽  
High Heat ◽  
High Repetition Rate ◽  
X Rays ◽  
Ray Optics ◽  
X Ray ◽  
Load Beam ◽  
High Heat Load

Next-generation high-brilliance X-ray photon sources call for new X-ray optics. Here we demonstrate the possibility of using monolithic diamond channel-cut crystals as high-heat-load beam-multiplexing narrow-band mechanically stable X-ray monochromators with high-power X-ray beams at cutting-edge high-repetition-rate X-ray free-electron laser (XFEL) facilities. The diamond channel-cut crystals fabricated and characterized in these studies are designed as two-bounce Bragg reflection monochromators directing 14.4 or 12.4 keV X-rays within a 15 meV bandwidth to 57Fe or 45Sc nuclear resonant scattering experiments, respectively. The crystal design allows out-of-band X-rays transmitted with minimal losses to alternative simultaneous experiments. Only ≲2% of the incident ∼100 W X-ray beam is absorbed in the 50 µm-thick first diamond crystal reflector, ensuring that the monochromator crystal is highly stable. Other X-ray optics applications of diamond channel-cut crystals are anticipated.

Characterization of nanocrystalline surface layer induced by shot peening and effect on their fatigue strength.

2004 ◽  
Vol 843 ◽  
Author(s):  
Hideo Mano ◽  
Kondo Satoru ◽  
Akihito Matsumuro ◽  
Toru Imura
Keyword(s):  
Residual Stress ◽  
Surface Layer ◽  
Fatigue Strength ◽  
Vickers Hardness ◽  
Shot Peening ◽  
White Layer ◽  
The Other ◽  
Fatigue Properties ◽  
Nanocrystalline Layer

ABSTRACTThe shot peening process is known to produce a hard layer, known as the white layer” on the surface of coil springs. However, little is known about the fatigue properties of this white-layer.In this study, coil springs with a white-layer were manufactured. The surface of these springs was then examined using micro Vickers hardness, FE-SEM etc. to test fatigue strength of the springs.From the results obtained, a microstructure of the white-layer with grain size of 50–100 nm was observed, with a Vickers hardness rating of 8–10 GPa.Tow category springs were manufactured utilizing a double-peening process. These springs had the same residual stress destruction and surface roughness. Only one difference was observed: one spring had a nanocrystalline layer on the surface, while the other did not. The results of the fatigue test realized an increase in the fatigue life of the nanocrystalline surface layer by 9%.

Isoelastic Cementless Total Hip Replacement in Rheumatoid Arthritis. Long-Term Results

1992 ◽  
Vol 2 (2) ◽  
pp. 43-46
Author(s):  
U. Fusco ◽  
R. Capelli ◽  
A. Avai ◽  
M. Gerundini ◽  
L. Colombini ◽  
...  
Keyword(s):  
Rheumatoid Arthritis ◽  
Hip Replacement ◽  
The Other ◽  
Long Term Results ◽  
X Rays ◽  
X Ray ◽  
The Mean ◽  
Cementless Total Hip Replacement

Between 1980 and 1987 we have implanted 46 isoelastic cementless THR in 40 patients affected with rheumatoid arthritis. We have reviewed 38 hips clinically and by X-ray. The mean follow-up was 8,5 years. Harris hip scores ranged from 30.6 preoperatively to 73,4 post-operatively when reviewed. While on the other hand Merle D'Aubigné hip scores ranged from 7,06 pre-operatively to 15,59 post-operatively. All patients have been satisfied, and X-rays showed an improvement for both Charnely and Gruen X-ray score.

scholarly journals THE SKIN REACTIONS PRODUCED BY ALTERNATIONS OF HEAT AND X-RAY AT VARIOUS TIME INTERVALS

1931 ◽  
Vol 53 (3) ◽  
pp. 405-411 ◽  
Author(s):  
James A. Hawkins
Keyword(s):  
Guinea Pig ◽  
The Other ◽  
X Rays ◽  
Time Intervals ◽  
Skin Reactions ◽  
X Ray ◽  
Critical Dose

Areas on the abdomen of the same guinea pig were exposed to suberythemal doses of soft X-rays, to heat of an intensity below the critical dose for the production of burns, and to both radiations in sequence with various time intervals between the exposures. The only effect of exposure to X-ray or heat alone was a slight scaling of the skin. The areas exposed to heat and X-radiation developed well-marked and persistent burns when the exposure to one agent was made within 3 hours of the other. Scaling of the skin developed when the exposure to one agent was made 1 day after the other. This scaling was more marked and lasted longer than the scaling produced by either agent alone. The results were the same no matter in which sequence the agents were applied.

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