Marked Changes In Intensity Research Articles

Effective Young’s Modulus of Bacterial and Microfibrillated Cellulose Fibrils in Fibrous Networks

The deformation micromechanics of bacterial cellulose (BC) and microfibrillated cellulose (MFC) networks have been investigated using Raman spectroscopy. The Raman spectra of both BC and MFC networks exhibit a band initially located at ≈ 1095 cm(-1). We have used the intensity of this band as a function of rotation angle of the specimens to study the cellulose fibril orientation in BC and MFC networks. We have also used the change in this peak's wavenumber position with applied tensile deformation to probe the stress-transfer behavior of these cellulosic materials. The intensity of this Raman band did not change significantly with rotation angle, indicating an in-plane 2D network of fibrils with uniform random orientation; conversely, a highly oriented flax fiber exhibited a marked change in intensity with rotation angle. Experimental data and theoretical analysis shows that the Raman band shift rate arising from deformation of networks under tension is dependent on the angles between the axis of fibrils, the strain axis, the incident laser polarization direction, and the back scattered polarization configurations. From this analysis, the effective moduli of single fibrils of BC and MFC in the networks were estimated to be in the ranges of 79-88 and 29-36 GPa, respectively. It is shown also that for the model to fit the data it is necessary to use a negative Poisson's ratio for MFC networks and BC networks. Discussion of this in-plane "auxetic" behavior is given.

Structure, microstructure and photoluminescence properties of Fe doped SnO 2 thin films

In this paper, effects of Fe doping on crystallinity, microstructure and photoluminescence (PL) properties of sol–gel derived SnO 2 thin films are reported. It is shown that doping of Fe 3+ ions leads to crystallite size reduction and higher strain in SnO 2 thin films. The room temperature PL spectra show marked changes in intensity and blue-shift of the emission lines upon Fe doping. These observations have been correlated with structural changes and defect chemistry of Fe doped SnO 2 thin films.

Analysis of elastic strain and crystallographic texture in poled rhombohedral PZT ceramics

The elastic strain and crystallographic texture of a rhombohedral lead zirconate titanate ceramic have been characterised in the remanent state, after poling, using high-energy synchrotron X-ray diffraction as a function of the grain orientation ψ relative to the poling direction. It is observed that the (2 0 0) diffraction peak exhibits pronounced shifts as a function of ψ, indicating an elastic lattice strain, while others ({1 1 1}, {1 1 2} and {2 2 0}) show marked changes in intensity as a result of preferred ferroelectric domain orientation. It is shown that the (2 0 0) peak is not affected by the domain switching itself but rather acts like an elastic macrostrain sensor. A simple Eshelby analysis is used to demonstrate that both the elastic strain and texture vary systematically with ψ according to the factor (3cos 2 ψ − 1). This angular dependence is evaluated through micromechanics modelling. The physical meaning of the texture variations with ψ is also discussed.

Acute focal cerebral ischemia in rats studied by diffusion-weighted magnetic resonance imaging—An experimental study

Temporary occlusion of the cerebral artery is occasionally repeated during neurosurgical operations, but the safety of such a procedure remains to be studied further. We studied early changes and reversibility of focal cerebral ischemia and the cumulative effects of repeated ischemic insults in rats using magnetic resonance imaging (MRI). Diffusion-weighted magnetic resonance images (DWI) and determination of signal intensity ratio (SIR) proved to be a valuable measure of studying early changes and reversibility of transient focal cerebral ischemia and cumulative adverse effects of repeated ischemic insults. DWIs showed marked intensity changes shortly after focal cerebral ischemia, while T2-weighted images failed to show hyperintensities until 2.5 hours after the onset of permanent ischemia. The critical period of ischemia in this model was 60 minutes. However, 20 minutes ischemia, when repeated twice with 60 minutes reperfusion in between, showed irreversible damage. Repeated insults of focal regional cerebral ischemia may cause irreversible tissue damage even if each ischemic period is less than the critical one.

FAR‐INFRARED SPECTRA OF LANGMUIR‐BLODGETT FILMS OF CHLOROPHYLL a, CHLOROPHYLL b, PHEOPHYTIN a and THEIR ADDUCTS WITH WATER and DIOXANE*

AbstractFourier transform infrared spectra in the low frequency region (500–150cm−1) of Langmuir‐Blodgett films of chlorophyll a (Chi a), chlorophyll b (Chi b) and pheophytin a have been studied. Correlations between spectral changes in monolayer and multilayers of Chi a and Chi b and their adducts with water and dioxane have been established.Spectroscopic evidence has indicated that, although there are no individual absorption bands that can be assigned to pure Mg‐nitrogen and/or Mg‐oxygen stretching or bending modes, there are several bands in the400–200 cm−1 region of the spectra containing considerable contributions from metal‐nitrogen and metal‐oxygen vibrational modes. These specific vibrations exhibit marked intensity changes and shifts upon water and dioxane interaction. The different states of chlorophyll aggregation in Langmuir‐Blodgett mono‐ and multilayers films resulted in noticeable changes in their far‐IR spectra.

Fluorescence and magnetic resonance spectra ofNd3+andEr3+ions in single crystals ofLaCl3

This article presents the results of experiments in which the 19 429.67-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ emission of an ${\mathrm{Ar}}^{+}$ laser is used to pump the ${Z}_{1}$, $^{4}\mathrm{I}_{9/2}$, \ensuremath{\mu}=(5/2\ensuremath{\rightarrow}${F}_{1}$, $^{2}\mathrm{G}_{9/2}$, \ensuremath{\mu}=(1/2 transition of ${\mathrm{Nd}}^{3+}$ ions dilutely substituted at ${\mathrm{La}}^{3+}$ sites in ${\mathrm{LaCl}}_{3}$ crystals in an \ensuremath{\sim}1.6-K bath of liquid He. In some of the work ${\mathrm{Er}}^{3+}$ ions are also present. When an external magnetic field is applied electron paramagnetic resonance (EPR) absorption of microwave energy by either ${\mathrm{Nd}}^{3+}$ or ${\mathrm{Er}}^{3+}$ results in marked intensity changes of ${\mathrm{Nd}}^{3+}$ fluorescence emissions. The essential new feature of this work is the observation of the importance of the effects of the heating of the crystal above the bath temperature by both optical and microwave absorption. The heating by phonons generated in the radiationless transitions associated with the optical pumping cycle results in the emission of 17 E and D ${\mathrm{Nd}}^{3+}$ fluorescences not observed in previous work with the crystal at \ensuremath{\sim}1.6 K. Because of the encapsulation of the crystals in silica envelopes in these experiments, the heating effects are especially marked at higher laser powers.These new fluorescences result from the state population redistributions effected by the rise in temperature of the crystal. EPR microwave absorption by either ${\mathrm{Nd}}^{3+}$ or ${\mathrm{Er}}^{3+}$ accompanied by spin-lattice relaxation results in a further increase in crystal temperature and further ${\mathrm{Nd}}^{3+}$ state population redistributions with concommitant changes in the intensities of the fluorescence emissions from these states of ${\mathrm{Nd}}^{3+}$. This affords a new mechanism for optically detected magnetic resonance (ODMR) of these rare-earth ions. This new mechanism for ODMR produces optical signals strikingly different from those previously studied which result from the changes in the populations of the two components of the ground ${Z}_{1}$ doublet of ${\mathrm{Nd}}^{3+}$ produced by ${Z}_{1}$ microwave absorption or by microwave absorption by the ${\mathrm{Er}}^{3+}$ ground doublet with subsequent transfer of Zeeman quanta between ${\mathrm{Er}}^{3+}$ and ${\mathrm{Nd}}^{3+}$ and resultant changes in optical pumping rates and fluorescence emissions. The factors contributing to the new mechanism for ODMR also account for the observed changes with temperature in the characters of the decays of the ODMR signals when microwave irradiation is terminated. With constant intensity laser irradiation in the absence of external magnetic fields the 28 observed fluorescence emissions oscillate in synchrony at frequencies (1/2 to (1/3 Hz, when the laser irradiation intensity lies in a certain narrow range. Several mechanisms considered as explanations of this phenomenon have failed to account for its observed features. It is clear, however, that these oscillations of emission intensity are accompanied by oscillations in the temperature of the crystal and of the populations of the emitting states.

Near-infrared-induced conformational isomerization of 2-chloroethanol in an argon matrix

The infrared spectrum of 2-chloroethanol in a low-temperature Ar matrix shows marked intensity changes in the OH and CCl stretching reg

Ultrastructural changes in kidney, myocardium and skeletal muscle of the dog during excessive mobilization of free fatty acids

Ultrastructural changes have been studied in kidney, myocardium and skeletal muscle of dogs during excessive mobilization of free fatty acids induced by continuous infusion of noradrenaline. A special type of cytoplasmic body appears in all three organs. Because of the close correspondence with respect to size, localization and frequency between these bodies and simultaneously appearing sudanophilic droplets in light microscopical preparations, they are referred to as “lipid bodies” and assumed to represent triglyceride deposited as the fatty acids taken up by the cells become esterified. In the kidney, most lipid bodies are seen in the proximal tubule epithelium. In the heart, they appear in all fibers, whereas in skeletal muscle, there are fibers with abundant, moderate and slight amounts. There are no obvious connections between the lipid bodies and cytomembranes or sarcotubular system. However, especially in myocardium and skeletal muscle but also to some extent in the kidney, mitochondria are seen in close proximity to lipid bodies. There seems to be no membrane structure around lipid bodies which in the present series contained a material with varying electron density. No information about the mechanisms for uptake and transport of fatty acids into cells was obtained. There was no obvious damage to the cell structures including the mitochondria, in spite of the marked change in intensity and distribution of the succinic dehydrogenase reaction in light microscopical preparations.

The Spectrum of Rho Cassiopeiae I.

view Abstract Citations (33) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Spectrum of Rho Cassiopeiae I. Beardsley, Wallace R. Abstract This paper constitutes an analysis of an extensive series of spectrograms of p Cassiopeiae taken by several observers principally with the 82-inch telescope of the McDonald Observatory both during and after the deep minimum in light of 1946. Identification measures by Tai and Thackeray before the minirnurn have been combined with detailed measures by the writer during and after the mimmum to form a catalogue of the spectral lines as seen on plates of medium dispersion. A group of 23 selected zero-volt lines were analyzed for radial-velocity and intensity changes. A] though no change in radial velocity was detected, marked changes in intensity did occur. The hydrogen lines in p Cas in 1936 were found to be as strong as, or even stronger than, in CMa. Weakness of the hydrogen lines as early as 1939 may be evidence of spectral change leading up to the 1946 minimum. Evidence is cited for an overlying shell in which the TiO is formed. Unlike RV Tauri stars, the spectral type from line ratios at minimum light was also M3. The spectral type after minimum varied progressively from K5p to G5p, even reaching F8p during the "flare-up" of 1950. The behavior of emission in the hydrogen and Ca I X 4227 lines is discussed, as well as the presence of a sharp absorption core in Ca I. This core also was probably due to an overlying shell. Publication: The Astrophysical Journal Supplement Series Pub Date: February 1961 DOI: 10.1086/190058 Bibcode: 1961ApJS....5..381B full text sources ADS | data products SIMBAD (2)

The attenuation of short wireless waves at the surface of the Earth

An apparatus is described for measuring relative field intensities of wireless waves of the order of 20 metres, and the results of a series of measurements taken with it on wavelengths of approximately 25 metres for distances of from 200 ft. to 60 miles from the transmitter are shown as “Intensity/Distance” curves. For distances greater than 2 miles the decrease of intensity is found to be approximately proportional to the inverse square of the distance as predicted by the theory of Sommerfeld. For shorter distances, however, the curves are much straighter than predicted by theory. This is attributed to penetration of the waves to layers of higher conductivity below the surface. This is supported by the increase in the variations in attenuation with change of surface observed on a wavelength of 18 metres and by measurements on the “tilt” of the electric vector of the wave-front.In all cases, marked changes in intensity and attenuation were found to occur with apparently slight changes of surface and slope of the ground.

The attenuation of short wireless waves at the surface of the earth

An apparatus is described for measuring relative field intensities of wireless waves of the order of 20 metres, and the results of a series of measurements taken with it on wavelengths of approximately 25 metres for distances of from 200 ft. to 60 miles from the transmitter are shown as“Intensity/Distance” curves. For distances greater than 2 miles the decrease of intensity is found to be approximately proportional to the inverse square of the distance as predicted by the theory of Sommerfeld. For shorter distances, however, the curves are much straighter than predicted by theory. This is attributed to penetration of the waves to layers of higher conductivity below the surface. This is supported by the increase in the variations in attenuation with change of surface observed on a wavelength of 18 metres and by measurements on the “tilt” of the electric vector of the wave-front.In all cases, marked changes in intensity and attenuation were found to occur with apparently slight changes of surface and slope of the ground.

The Effect of Temperature on the Absorption Bands of Fused Quartz in the Infra-Red

The absorption bands of specimens of fused quartz, ranging in thickness from 2.0 mm for the 3\ensuremath{\mu} region, to 4\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$ mm for the 8\ensuremath{\mu} region, were studied. In regions where sufficient energy was available, an echelette grating was used to give greater dispersion. Measurements were taken at room temperature and at 850\ifmmode^\circ\else\textdegree\fi{}C. In accord with previous work, the absorption band in the region of anomalous dispersion at 9\ensuremath{\mu} was found to shift toward longer wave-lengths with increasing temperature. With higher resolution, however, fine structure bands were found which did not shift with the temperature, but did undergo marked changes in intensity. Several sharp bands between 2 and 4\ensuremath{\mu} were found to remain fixed as the temperature was changed. A broad band which proved to be double, was found at 12.5\ensuremath{\mu}. These bands did not shift with temperature. In most cases, there was a marked change in intensity with temperature. It was found that inside the strong bands, the absorption was much less at high temperatures, while outside the bands, the reverse was the case.