Definite Minimum Research Articles

Effect of interconnecting area between the ends of a sliding bearing on film thickness

The effect of the area of interconnections between the ends of fast-acting bearings, such as those of concentric recoil mechanisms used with American tank guns, has been studied. It was found that the bearings do not ‘starve’ with a small interconnection area, but larger areas produced thicker fluid films. However, if the interconnection area was greater than 15–20 mm 2 with the system studied (5.08 cm diameter shaft), the resulting film-thickness decreased from the maximum. With this system, there was a definite minimum at 7.4 mm 2. There was also probably another at about 26 mm 2, but it was not so well-defined. In addition, the film-thickness usually continued to increase for a time even after the movement of the sliding shaft has stopped.

Chasing A Receding Zero: Impact of the Zero Threshold Concept on Actions of Regulatory Officials

The principle of toxicological threshold was stated in 1564 by Paracelsus as “All things are poisonous, yet nothing is poisonous. Dosage alone determines poisoning.” This principle remains valid, even with consideration of today's public concern with low-dosage effects of compounds that are categorized as carcinogens, mutagens and teratogens. Modern laboratory methods enable detection of increasingly small traces of such compounds in foods. The search for these has been termed “Chasing a receding zero, ” and this quest has been stimulated by statements that no one knows how small an amount of a carcinogen, taken for how short a time, can induce cancer, and that even one molecule of a carcinogen, acting on a single cell, can transform a normal cell into a cancer cell. This latter proposal is a stochastic impossibility. Every cell contains millions of carcinogenic molecules. Examples are arsenic, cadmium and chromium. In addition, there are estrogens and other steroid hormones present in each cell and needed for normal bodily functions. These substances are regarded as carcinogens because of their effect at high levels on increasing the cancer rate in experimental animals. Obviously, there must be a threshold for this effect. An estimate has been made by Dingman that “a threshold for biological activity exists within a cell at 10, 000 atoms.” It is also obvious that there is a threshold for deficiencies that induce cancer, such as that of iodine. Iodine deficiency is mimicked by administration of goitrogens, and these are present naturally at low to moderate levels in many common foods. The threshold principle is stated by Claus and Bolander to be a law of nature, valid in many circumstances, and governing the fact that a causative agent must be present in a quantity exceeding a definite minimum in order to produce the effect.

Diurnal fluctuations of cell kinetic parameters in the epidermis and the sebaceous gland of the hamster ear

By using the colcemid method, the presence of a diurnal variation for the mitosis index was confirmed, showing a definite minimum during the night in the sebaceous gland of the Syrian hamster ear. Furthermore, the number of all labelled cells and the quotient "single-labelled 14C-cells + double-labelled cells/single-labelled 3H-cells" determined with double-labelling autoradiography ([3H] and [14C]thymidine) seem to be subject to rhythmic fluctuations, although statistical support for this observation is lacking. The parallelism of the rhythmic variations in the epidermis and in the sebaceous glands is striking.

A SOLID STATE RESISTANCE CONTROLLER FOR 3-PHASE SLIP-RING INDUCTION MOTOR

ABSTRACT A solid state rotor resistance controller incorporating triacs for varying the speed of 3-phase slip-ring Induction motor delivering a constant load torque is presented. Using this controller, it is possible to vary the speed of the motor continuously from a definite minimum speed to a definite maximum speed. The controller is simpler and more reliable compared to phase controlled or chopper controlled resistance controllers.

Molecular architecture and physicochemical properties of some vinyl alcohol‐vinyl acetate copolymers

AbstractTwo series of vinyl alcohol‐vinyl acetate copolymers were prepared by homogeneous and heterogeneous acetylation of the same precursor poly(vinyl alcohol). Their intramolecular monomer distributions were analyzed by IR spectrometry, calorimetry, and differential thermal analysis. The results show a more blocky distribution for the heterogeneously prepared copolymers. The properties of these (co)polymers in dilute aqueous solution were determined by means of viscometry. Whereas the copolymer‐solvent interaction parameter of the homogeneously acetylated, random copolymers hardly varied with acetate content, a definite minimum was found for the blocky copolymers at about 7 mole% vinyl acetate. These findings were attributed to the incompatibility of dissimilar sequences, which sharply decreases with decreasing vinyl acetate sequence length. Up to about 17 mole% vinyl acetate content, the solvent quality for the copolymers is at least as good as for poly(vinyl alcohol). In addition, the dilute solution properties of the samples were established in water saturated with 1‐butanol. For copolymers with up to about 17 mole% vinyl acetate, at 25°C this mixture is a better solvent than water. The highest increase in solvent quality was found for the homopolymer, whereas the increase diminished with acetate content, irrespective of the intramolecular vinyl acetate distribution. These findings are explained in terms of preferential adsorption of 1‐butanol onto the (co)polymer backbone due to hydrophobic interactions and prevention of this process by the bulky acetate groups.

Optimal shift strategy for a block-transfer CCD memory

For the purposes of this paper, a block-transfer CCD memory is composed of serial shift registers whose shift rate can vary, but which have a definite minimum shift rate (the refresh rate) and a definite maximum shift rate. The bits in the shift registers are numbered 0 to N - 1, and blocks of N bits are always transferred, always starting at bit 0. What is the best shift strategy so that a block transfer request occurring at a random time will have to wait the minimal amount of time before bit 0 can be reached? The minimum shift rate requirement does not allow one to simply “park” at bit 0 and wait for a transfer request. The optimal strategy involves shifting as slowly as possible until bit 0 is passed, then shifting as quickly as possible until a critical boundary is reached, shortly before bit 0 comes around again. This is called the “hurry up and wait” strategy and is well known outside the computer field. The block-transfer CCD memory can also be viewed as a paging drum with a variable (bounded) rotation speed.

Thymine content of sea water as a measure of biosynthetic potential

A hydrolysis procedure along with a high-pressure liquid chromatographic procedure is given enabling simple and reliable thymine determinations in the nanogram range in different fractions of sea-water samples taken from three different locations in the Northern Adriatic Sea. The levels corresponded to 1–3 μg DNA per liter. From total polyanionic thymine, which had been precipitated as the cetyltrimethylammonium salt, the highest percentage was linked to the particulate fraction, with a definite subsurface minimum at 10 to 15 m. There was a corresponding maximum of a high molecular “non-particulate” thymine-containing fraction at the corresponding depth. From the bottom at 30 m upwards to about 20 m, a low molecular thymine-containing material has been found. Remarkably these basic features were common to all three locations, one of which was supposed to be in clean water, one near a thickly settled, touristic area, and the other in front of a large river delta coming from industrial hinterland.

ChemInform Abstract: AB INITIO STUDY OF THE STRUCTURE, ISOMERS AND VERTICAL ELECTRONIC SPECTRUM OF THE FORMYL RADICAL HCO

Chemischer InformationsdienstVolume 7, Issue 29 Physical Organic Chemistry ChemInform Abstract: AB INITIO STUDY OF THE STRUCTURE, ISOMERS AND VERTICAL ELECTRONIC SPECTRUM OF THE FORMYL RADICAL HCO PABLO J. BRUNA, PABLO J. BRUNASearch for more papers by this authorROBERT J. BUENKER, ROBERT J. BUENKERSearch for more papers by this authorSIGRID D. PEYERIMHOFF, SIGRID D. PEYERIMHOFFSearch for more papers by this author PABLO J. BRUNA, PABLO J. BRUNASearch for more papers by this authorROBERT J. BUENKER, ROBERT J. BUENKERSearch for more papers by this authorSIGRID D. PEYERIMHOFF, SIGRID D. PEYERIMHOFFSearch for more papers by this author First published: July 20, 1976 https://doi.org/10.1002/chin.197629060AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume7, Issue29July 20, 1976 RelatedInformation

Ab initio study of the structure, isomers and vertical electronic spectrum of the formyl radical HCO

Non-empirical SCF and CI calculations are reported for the HCO radical in various lowlying excited states. Potential curves for hydrogen bending and hydrogen abstraction are investigated for both, the HCO and COH form of the system. The dissociation energy of HCO is calculated to be 18.8 kcal mol −1, in good agreement with more recent experimental measurements; the unpaired electron density is shown to be located in a σ-type orbital with significant amount of hydrogen character. The COH isomer is found to be less stable than HCO by approximately 23 kcal mol −1; its potential energy surface shows a definite local minimum at a somewhat smaller angle (~ 120° ) and a significantly larger CO bond length than is calculated for HCO, but the COH system is not found to be bound with respect to the separated species H + CO. The assignment of the first spectral band as resulting from X 2A' to a linear 2Π state of the same electronic configuration is supported by the calculations. The second observed band system is found to involve transitions (of nearly equal intensity) to a (linear) Rydberg ( 3s) and a strongly bent valence (6 a'→ 7 a') upper state of the same symmetry; mixing of these states might cause irregularities seen in the emission and absorption spectrum. Vertical excitation energies and oscillator strengths to higher-lying Rydberg and valence states are also reported.

Spontaneous fluctuations of the emission from a laser with a transversely inhomogeneous field distribution

An investigation is made of the influence of a transverse macroinhomogeneity in a solid state laser on the emission kinetics. It is shown that when a fairly definite minimum is located in the central part of the transverse intensity distribution, the emission is in the form of spontaneous fluctuations whose growth increment increases with increasing depth of this minimum. The results obtained are in agreement with the experimental data on the correlation between the transverse field distribution and the laser emission kinetics.

Reaction of halogenoacetylenes with sulphur nucleophiles studied by extended Hückel molecular orbital theory

Extended HMO calculations have been carried out for the reactions of 1-halogeno-2-methyl- and 1-halogeno-2-phenylacetylenes with HS–, in order to compare different positions of attack by the nucleophile (C-1, C-2, or halogen). Potential energy surfaces in the region of possible reaction intermediates have been obtained, and some definite minima have been found. Attack at C-1 appears to be favoured when halogen is F or Cl for both alkyl and aryl derivatives. Computations favour halogen attack in the case of iodo(phenyl)acetylene. Both kinds of attack seem possible for bromo(phenyl)acetylene. These results compare well with the outcome of experiments.

Diurnal variations of protein and electrolyte concentrations and of acid-base status in plasma and red cells of normal man.

Venous blood was sampled in 3-h intervals from 5 men and 4 women under conditions of normal daily activity during 24 h (Series I). Hematocrit, hemoglobin concentration in blood and red cells, sodium, potassium, magnesium and chloride concentrations in plasma and red cells, protein, calcium and inorganic phosphate concentrations and standard bicarbonate in plasma, pH in blood and red cells, pCO2 in blood were measured or calculated. Most concentration curves showed biphasic patterns with night minima which were significant for hemoglobin, hematocrit and pH in blood, protein, sodium, calcium and standard bicarbonate in plasma, potassium and pH in red cells. Inorganic phosphate in plasma alone exhibited a definite day minimum. A second series (6 subjects) with measurements made only between 06.00 and 12.00 showed changes similar to those in Series I with an additional small increase of red cell sodium concentration at noon. In a third series, where 6 subjects remained in a recumbent position up to midday, the morning increase of [Hb], Hct, pH and standard bicarbonate was clearly reproducible.

Anharmonic Models and Thermal-Expansion Calculations for KBr

The mode-Gr\uneisen parameters, the macroscopic Gr\uneisen function $\ensuremath{\gamma}(T)=3\ensuremath{\alpha}{B}^{\mathrm{is}}\frac{V}{{C}_{V}}$, and the coefficient of thermal expansion $\ensuremath{\alpha}$ are calculated for KBr. Three anharmonic models are used: the rigid-ion (RI) model, a deformation-dipole (DD) model in which the deformability of the ions does not depend on the volume $V$, and a DD model in which the deformability does depend on $V$. Allowing the deformability to depend on $V$ significantly improves the agreement with experiment. A definite minimum in the low-temperature values of $\ensuremath{\gamma}(T)$ is predicted by the DD models, but not by the RI model. The distance between nearest neighbors $r$ at which the potential energy of the lattice has its minimum value is found self-consistently. This value of $r$ is used in the determination of the derivatives of the short-range overlap potential $\ensuremath{\nu}(r)$. The force constants obtained differ significantly from those obtained by substituting room-temperature experimental data into formulas derived using the equilibrium condition. Significantly larger values for $\ensuremath{\gamma}(T)$ and $\ensuremath{\alpha}$, which are in better agreement with the experimental results, are obtained by allowing for the temperature dependence of the zero-pressure values of ${B}^{\mathrm{is}}$ and $r$.

Conformation of cytochromes: IV. Conformational homology of functionally homologous cytochromes c

The conformational homology of functionally homologous cytochromes c from horse, beef, tuna, turkey, pigeon and moth has been investigated by comparison of the circular dichroism (CD) spectra of each preparation in both oxidation states of iron and in the wavelength region 600-185 mμ at pH 6.8. In the oxidized state all preparations exhibit similar dichroic features with only small variations in the relative magnitudes of various extrema, except for the aromatic circular dichroism curve for tuna cytochrome c. The preparations in the reduced state of iron also exhibit comparable dichroic spectra, both in the region of the Soret transition and the intrinsic absorption region. The CD patterns for the reduced cytochromes in the α-β absorption region, however, exhibit deviations suggestive of small but distinct differences in the electronic asymmetry of the prosthetic groups, especially of the porphyrin moiety, possibly because of differences in the electronically coupled chromophores. A gross conformational homology among various mammalian-type cytochromes c has, therefore, been suggested. The dichroic differences in the case of tuna cytochrome c have been imputed to be a reflection of an unusually asymmetric environment of the residue at position 33 of the polypeptide chain. The intrinsic CD curves above 200 mμ for all the preparations in both valence states of heme iron exhibit features characteristic of the presence of α-helical structures in the molecule. Below 200 mμ, however, the dichroic curves exhibit a single positive maximum at about 194 mμ and a definite minimum at 190 mμ. The former feature is usually associated with systems containing β-structure. The presence of a minimum at about 190 mμ, when taken in conjunction with the characterizing features for α-helical models (a large positive maximum at this wavelength), indicates the absence of α-helically organized structure in the molecule. An analysis of the conformation of the protein moiety in terms of proportions of reference model conformations (α-helix, β-structure and random coil) and based on the recently developed isodichroic method 24 confirms the low α-helical content of various cytochromes and further demonstrates the gross polypeptide conformational homology for various functionally homologous preparations.

Minima in Generalized Oscillator Strengths: C2H4

A characteristic of electron impact excitation of low-lying Rydberg states is a minimum in the generalized oscillator strength as a function of K, the momentum transfer. This characteristic is used as a probe of the Rydberg character of four transitions in C2H4. Three, the Ag1 → 1B3u(π → 3s + 3s), 1Ag → 1B3u(π → 3pz − 3pz), and Ag1 → 1B3u(π → 4s) transitions, have long been identified as Rydberg and are found to exhibit the characteristic minimum. A fourth transition Ag1 → 1B1u(π → π*) is normally termed a valence excitation, and a theoretical calculation using Hartree–Fock molecular orbitals had predicted no minimum. For an energy loss of 8.0 eV which is identified with the valence transition a definite minimum is observed. Speculation on the source of this anomaly centers on a type of valence–Rydberg configurational mixing which can occur in many molecules. It is suggested that the presence or absence of minima in generalized oscillator strength curves be used to probe this aspect of the character of the excited state.

Spectrofluorometric studies. III. Ortho- and para-difluorobenzene

Spectrofluorometric techniques have been used to determine gas phase singlet and triplet yields in ortho- and para-difluorobenzene as a function of exciting wavelength and pressure. The importance of the "around the corner effect" in such measurements as the cause of large errors is briefly discussed.In the case of ortho-difluorobenzene, maxima in fluorescent yield are produced by the exciting wavelengths 2490, 2580, and 2700 Å; minima at 2540 and 2660 Å. Triplet yields, using the sensitized biacetyl emission technique, have been determined at 2500, 2580, 2660, and 2700 Å. The sums of the singlet and triplet yields at these wavelengths are 0.34, 0.52, 0.75, and 0.97 respectively.Para-difluorobenzene has the largest quantum yield of fluorescence of any fluorinated benzene yet examined. The fluorescent yield shows only one definite minimum at 2740 Å. Triplet yields have been determined at 2660, 2740, and 2760 Å. The sums of the singlet and triplet yields at these wavelengths are 0.5, 0.5, and 0.7 respectively.

Experimental study of UHF mobile radio transmission using a directive antenna

Propagation experiments were run at 836 Mc between a fixed omnidirectional base station and a mobile station using a directional antenna. On typical residential streets it was found that the antenna orientation had only a small effect on the average signal level and that the fading rate was significantly reduced. It was also discovered that the fading rate expressed as a function of antenna direction has definite minima and maxima. These are related to two factors, the direction of motion of the vehicle and the direction from the vehicle to the base station. In general, minimum fading occurs along and at right angles to the direction of motion and in the direction of the base station.

PROTECTION AGAINST WAVE ACTION BASED ON HYDROELASTIC EFFECT

The authorfe conception on the mechanism of continuous slope protection under wave action (elements of flexible screen theory) are given in the paper in brief. Slope structures with continuous revetments are widely used in the Soviet Union, not only in canals but even in large reservoirs where waves reach nearly sea wave height. When ordinary design methods are used, strength and stability of the revetment is provided by its thickness increase, and an expensive filter layer is placed under the revetment, Though continuous revetments were expensive, slope structures proved to be cheaper and more reliable than other measures of protection against wave action. Now it appears that the revetment's stress conditions may be improved by reducing its thickness and eliarijaatiyjtfee filter layer. There are types of coverings, the flexibility of which contributes to the self-consolidation of sand soil, filling the voids, and reducing the effective wave pressure. There exists however a definite thickness minimum (critical rigidity) below which dangerous slope deformations occur. The various attempts to determine this critical rigidity are shortly reported below. Results of laboratory and field tests are given, permitting to get knowledge of physical processes occurring under the revetment and of structural features improving their reliability,

Three-color Photometry of SX Cassiopeiae.

view Abstract Citations (2) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Three-color Photometry of SX Cassiopeiae. Shao, Cheng-Yuan Abstract Photoelectric observations of this long-period (36d.57) eclipsing binary (sgA6+gG6) were made on 66 nights at Harvard's Agassiz Station during 1961-1963. These observations, extending over 21 revolutions of the system, define the shape of the light and the color curves in a homogeneous form and reveal various interesting features. (1) The duration of primary eclipse is about 3d.6 and that of totality about 1d.3. These durations seem to be the same in all three colors. Therefore, the present material does not show variation of width of minimum with wavelength of observation. (2) Outside eclipse, the light and colors show large scatter due to erratic variations. Considerable fluctuations on shoulders of primary eclipse are observed. The amplitudes of these variations and fluctuations are greater in shorter wavelength regions. But the star appears to be constant at totality in different cycles. Also, the maximum after primary eclipse is higher than that preceding to it. (3) The observed ellipticity effect is more pronounced in the V than that in the B curve. The U curve is less complete, but it seems to have no observable ellipticity and no definite secondary minimum. (4) The magnitude and colors of SX Cas in the UBV system are V B-V U-B Maxinium 8rn.96 +0rn.72 +O~~20 Primary minimum 9.83 +1.32 +0.59 Secondary minimum 9.32 +0.56 +0.05 (5) When the observed color indices are corrected for a rough reddening value of Ey~0~3, the unred- dened U-B color at secondary minimum resembles that of an early A type supergiant and the unreddened B - V color at primary minimum is similar to that of a late G or KO star of class III or IV. Thus, we find an ultraviolet excess of about O~~~3 at totality. The ultraviolet excess may be the same effect recently reported by Popper and Walker (Astron. J. 68, 543, 1963) for some similar eclipsing systems. Publication: The Astronomical Journal Pub Date: 1965 DOI: 10.1086/109643 Bibcode: 1965AJ.....70S.147S full text sources ADS |

Change in Thermal Conductivity upon Low-Temperature Electron Irradiation: GaAs

Measurements of the change in thermal conductivity of high-purity single-crystal GaAs were made upon 2-MeV electron irradiation and annealing. Two GaAs samples were irradiated at maximum temperatures of 100 and 80\ifmmode^\circ\else\textdegree\fi{}K. A linear increase in the additive thermal resistivity near 50\ifmmode^\circ\else\textdegree\fi{}K is observed upon bombardment. The results yield $\frac{1}{K}\ensuremath{-}\frac{1}{{K}_{0}}=(3.15\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}19}$ cm-deg/W per 2-MeV electron/${\mathrm{cm}}^{2}$. The experimental ratio of the point-defect thermal resistivity to the induced lattice strain at 50\ifmmode^\circ\else\textdegree\fi{}K is $\frac{(\frac{1}{K}\ensuremath{-}\frac{1}{{K}_{0}})}{(\frac{3\ensuremath{\Delta}L}{L})}=(1.0\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}{10}^{4}$ cm-deg/W. Using estimates for the introduced defect concentration (based upon the change in strain rate as a function of electron energy) together with the observed increase in thermal resistivity, one obtains $\frac{1}{K}\ensuremath{-}\frac{1}{{K}_{0}}=(94\ifmmode\pm\else\textpm\fi{}10)\ifmmode\times\else\texttimes\fi{}{10}^{2}C$ cm-deg/W, where $C$ is the fractional point-defect concentration. This value is intermediate between those predicted by the point-defect scattering theories of Klemens and Ziman. Isochronal anneals carried out above 50\ifmmode^\circ\else\textdegree\fi{}K with all measurements made at 50\ifmmode^\circ\else\textdegree\fi{}K demonstrate low-temperature annealing in GaAs. Annealing is observed to begin near 55\ifmmode^\circ\else\textdegree\fi{}K and accelerate near 190\ifmmode^\circ\else\textdegree\fi{}K. About 70% of the additive thermal resistivity stable at 50\ifmmode^\circ\else\textdegree\fi{}K anneals below 325\ifmmode^\circ\else\textdegree\fi{}K. Definite minima are observed in the temperature dependence of the thermal conductivity, suggesting localized-impurity-mode scattering. The annealing, however, takes place over too large a temperature range to be due to a single thermally activated process. The change in shape of the temperature dependence of the thermal conductivity upon annealing indicates that below 325\ifmmode^\circ\else\textdegree\fi{}K the defects anneal as point defects. For anneal temperatures between 325 and 575\ifmmode^\circ\else\textdegree\fi{}K the point defects no longer remain isolated, and clustering or precipitation is suggested.