A Simple Model for the Mean and Difference of NH-Stretching Frequencies for NH2 Groups, and Its Application to Results of Some ab initio Vibrational-Frequency Calculations

1988 ◽  
Vol 41 (3) ◽  
pp. 387
Author(s):  
NV Riggs ◽  
L Radom
Keyword(s):  
Ab Initio ◽  
Molecular System ◽  
Lone Pair ◽  
Exceptional Case ◽  
Force Constants ◽  
Gauche Conformation ◽  
The Mean ◽  
The Difference ◽  
Lone Pair Electrons ◽  
The Given

The expression for the sum of the eigenvalues of the 2×2 GF matrix for two interacting NH bonds suggests that the mean NH-stretching frequency for an NH2 group should be closely proportional to ( Σf )½, where Σf is the sum of the two corresponding force constants. Ab initio results for the NH2 groups in various conformations of ethanamine , hydrazine and 1,1-dimethylhydrazine confirm such constancy to within 0.1%. The corresponding expression for the difference of the eigenvalues suggests, counterintuitively, that the difference of NH-stretching frequencies for an NH2 group in a given molecular system should also be largely proportional to ( Σf )½ and, except for the gauche conformation of 1,1-dimethylhydrazine, ab initio results for the above molecules support this suggestion to within �14 cm-1. In the exceptional case, the difference of NH-stretching force constants makes a much larger than usual contribution. Relative values of the force constants for various molecular species may be interpreted in terms of the relative geometries and effects of donation of lone-pair electrons at an adjacent centre into antibonding N-H orbitals at the given centre.

VUV FRAGMENTATION OF SOME HYDROFLUOROCARBON CATIONS STUDIED USING COINCIDENCE TECHNIQUES

2002 ◽  
Vol 09 (01) ◽  
pp. 153-158 ◽  
Author(s):  
WEIDONG ZHOU ◽  
D. P. SECCOMBE ◽  
R. Y. L. CHIM ◽  
R. P. TUCKETT
Keyword(s):  
Kinetic Energy ◽  
Ab Initio ◽  
Ground State ◽  
Lower Energy ◽  
Lone Pair ◽  
Electronic States ◽  
Photoelectron Spectra ◽  
Highest Occupied Molecular Orbital ◽  
Impulsive Model ◽  
Lone Pair Electrons

Threshold photoelectron–photoion coincidence (TPEPICO) spectroscopy has been used to investigate the decay dynamics of the valence electronic states of the parent cation of several hydrofluorocarbons (HFC), based on fluorine-substituted ethane, in the energy range 11–25 eV. We present data for CF 3– CHF 2, CF 3– CH 2 F , CF 3– CH 3 and CHF 2– CH 3. The threshold photoelectron spectra (TPES) of these molecules show a common feature of a broad, relatively weak ground state, associated with electron removal from the highest-occupied molecular orbital (HOMO) having mainly C–C σ-bonding character. Adiabatic and vertical ionisation energies for the HOMO of the four HFCs are presented, together with corresponding values from ab initio calculations. For those lower-energy molecular orbitals associated with non-bonding fluorine 2pπ lone pair electrons, these electronic states of the HFC cation decay impulsively by C–F bond fission with considerable release of translational kinetic energy. Appearance energies are presented for formation of the daughter cation formed by such a process (e.g. CF 3– CHF +), together with ab initio energies of the corresponding dissociation channel (e.g. CF 3– CHF + + F ). Values for the translational kinetic energy released are compared with the predictions of a pure-impulsive model.

STEREOCHEMISTRY OF ARSENIC: VIII. CYANODIMETHYLARSINE (CACODYL CYANIDE)

1963 ◽  
Vol 41 (2) ◽  
pp. 460-464 ◽  
Author(s):  
N. Camerman ◽  
J. Trotter
Keyword(s):  
Charge Transfer ◽  
Lone Pair ◽  
The Other ◽  
Van Der Waals Interactions ◽  
Mean Values ◽  
Bond Lengths ◽  
Nitrogen Lone Pair ◽  
The Mean ◽  
Lone Pair Electrons ◽  
Crystallographic Axes

Crystals of cyanodimethylarsine, (CH3)2AsCN, are triclinic with two molecules in a unit cell of dimensions a = 6.31, b = 8.02, c = 6.27 Å, α = 110°00′, β = 119°45′, γ = 81°47′, space group [Formula: see text]. The structure has been determined from projections along the three crystallographic axes, and the mean values of the bond lengths and valency angles (with estimated standard deviations) are: As—C = 1.96±0.03 Å, C—N = 1.16 ± 0.07 Å, [Formula: see text], [Formula: see text], [Formula: see text]. There is an unusually short As … N intermolecular separation, which is indicative of charge-transfer bonding involving donation of nitrogen lone pair electrons to vacant arsenic 4d orbitals; the other intermolecular approaches correspond to normal van der Waals interactions.

scholarly journals THE STUDY OF THE DEPENDENCE OF SIZES OF MEASURED MICROSCOPIC OBJECTS AT THE POSITION OF THE SLICE PLANE

2019 ◽  
Vol 27 (4) ◽  
pp. 55-60
Author(s):  
A. E. Lun'kov ◽  
U. A. Gladilin ◽  
K. E. Ibragimova
Keyword(s):  
Distribution Function ◽  
Standard Deviation ◽  
Cross Sections ◽  
Mean Value ◽  
Distribution Functions ◽  
Distribution Law ◽  
The Mean ◽  
The Cross ◽  
The Difference ◽  
The Given

For microscopic objects in the form of spheres of different radii have been calculated the functions of distribution of the cross sections radii, taking into account the dependence on the position of the plane of the slice. Taking into account this dependence, the distribution functions of the cross sections radii of the spheres whose radii were given by the normal distribution law with the variation of its parameters were calculated. It is found that the difference between the given distribution function of the radii of spheres and the distribution function of their sections in the plane of the slice depends on the ratio of the standard deviation to the mean value of the radii. Depending on this relation, two simple algorithms are proposed to reconstruct the distribution function of the radii of objects by the distribution function of the radii of their sections. It is shown that these algorithms can be used to correct the experimental curve of the size distribution of micro-objects in the form of ellipsoid.

Ab initio 3-21 G Calculations of Push-Pull Interactions of Substituents at Imino-Nitrogen in Formamidines. Non-Equivalence of NO-Bonds of the Nitro-Substituent

1992 ◽  
Vol 47 (10) ◽  
pp. 1480-1490 ◽  
Author(s):  
Günter Häfelinger ◽  
Tadeusz Marek Krygowski ◽  
Frank K. H. Kuske
Keyword(s):  
Charge Density ◽  
Ab Initio ◽  
Amino Nitrogen ◽  
Lone Pair ◽  
Molecular Structures ◽  
Electron Charge Density ◽  
Imino Nitrogen ◽  
Bond Lengths ◽  
Mechanism Of Interaction ◽  
The Difference

Full ab initio 3-21 G optimization of molecular structures of twelve planar formamidines substituted by X in Ε-configuration at imino nitrogen (N2) (X = H, CH3, NH2, C6H5, OH, F, CHO, CN, BH2, NO (four isomers), NO2 (planar and perpendicular conformations), and CH2+) yielded the following conclusions: (1) as was found earlier experimentally, an increase of the shorter CN2 bond lengths is associated linearly with a decrease of the longer CN1 bond; (2) the difference of both CN distances (Δ CN) is related linearly to the Mulliken π-electron charge density at amino nitrogen (N1); (3) a decrease of Mulliken π-charge density (Δ qπ) at N1 is linearly related to a corresponding increase of Δ qπ at N2. The scatter and a slope of –0.54 indicate a mixed mechanism of interaction between NH2 and the substituents at amino nitrogen composed of n-π-conjugation and through conjugation; (4) an increase of σ-charge density at H2 is correlated with an increase of N1 – H2 bond lengths. As a result of interaction between the lone pair at N2 and the cis-bond of the nitro substituent this bond is calculated to be significantly shorter than the other one by 0.042 A. The same effect is calculated for the E-isomer of C-nitro substituted formamidine (Δ = 0.037 A) in contrast to the corresponding Z-isomer (Δ = 0.004 Å). A selection of experimental X-ray determinations of nitro-substituted compounds confirm this effect.

The Effect of Vocabulary Intervention on Text Comprehension: Who Benefits?

2019 ◽  
Vol 50 (4) ◽  
pp. 562-578 ◽  
Author(s):  
Dawna Duff
Keyword(s):  
Middle School ◽  
Reading Comprehension ◽  
Text Comprehension ◽  
Classroom Instruction ◽  
Vocabulary Instruction ◽  
Clinical Intervention ◽  
Vocabulary Knowledge ◽  
Vocabulary Intervention ◽  
The Mean ◽  
The Difference

Purpose Vocabulary intervention can improve comprehension of texts containing taught words, but it is unclear if all middle school readers get this benefit. This study tests 2 hypotheses about variables that predict response to vocabulary treatment on text comprehension: gains in vocabulary knowledge due to treatment and pretreatment reading comprehension scores. Method Students in Grade 6 ( N = 23) completed a 5-session intervention based on robust vocabulary instruction (RVI). Knowledge of the semantics of taught words was measured pre- and posttreatment. Participants then read 2 matched texts, 1 containing taught words (treated) and 1 not (untreated). Treated texts and taught word lists were counterbalanced across participants. The difference between text comprehension scores in treated and untreated conditions was taken as a measure of the effect of RVI on text comprehension. Results RVI resulted in significant gains in knowledge of taught words ( d RM = 2.26) and text comprehension ( d RM = 0.31). The extent of gains in vocabulary knowledge after vocabulary treatment did not predict the effect of RVI on comprehension of texts. However, untreated reading comprehension scores moderated the effect of the vocabulary treatment on text comprehension: Lower reading comprehension was associated with greater gains in text comprehension. Readers with comprehension scores below the mean experienced large gains in comprehension, but those with average/above average reading comprehension scores did not. Conclusion Vocabulary instruction had a larger effect on text comprehension for readers in Grade 6 who had lower untreated reading comprehension scores. In contrast, the amount that children learned about taught vocabulary did not predict the effect of vocabulary instruction on text comprehension. This has implications for the identification of 6th-grade students who would benefit from classroom instruction or clinical intervention targeting vocabulary knowledge.

Efficacy and Safety of Oral Ivermectin and Topical Permethrin in the Treatment of Scabies

2020 ◽  
Vol 33 (1) ◽  
pp. 41-47
Author(s):  
Mohsena Akhter ◽  
Ishrat Bhuiyan ◽  
Zulfiqer Hossain Khan ◽  
Mahfuza Akhter ◽  
Gulam Kazem Ali Ahmad ◽  
...  
Keyword(s):  
Skin Diseases ◽  
Close Contact ◽  
Randomized Study ◽  
Sarcoptes Scabiei ◽  
Efficacy And Safety ◽  
Common Skin ◽  
Group A ◽  
The Mean ◽  
The Difference ◽  
Group B

Background: Scabies is one of the most common skin diseases in our country. It is caused by the mite Sarcoptes scabiei var hominis, which is an ecto-parasite infesting the epidermis. Scabies is highly contagious. Prevalence is high in congested or densely populated areas. Individuals with close contact with an affected person should be treated with scabicidal which is available in both oral and topical formulations. The only oral but highly effective scabicidal known to date is Ivermectin. Amongst topical preparations, Permethrin 5 % cream is the treatment of choice. Objective: To evaluate the efficacy & safety of oral Ivermectin compared to topical Permethrin in the treatment of scabies. Methodology: This prospective, non-randomized study was conducted at the out-patient department of Dermatology and Venereology of Shaheed Suhrawardy Medical College & Hospital over a period of 6 months, from August 2016 to January 2017. The study population consisted of one hundred patients having scabies, enrolled according to inclusion criteria. They were divided into two groups. group A was subjected to oral Ivermectin and the group B to Permethrin 5% cream. Patients were followed up on day 7 and 14 for assessment of efficacy and safety. Result: The mean scoring with SD in group A (Ivermectin) and group B (Permethrin) were 8.26 ± 2.22 and 7.59 ± 2.01 respectively at the time of observation. The difference between the mean score of the two group is not significant (p=0.117) the mean scoring with SD in group A and group B were 4.54 ± 2.05 and 1.64 ± 1.84 respectively at 7thdays. The difference between the mean score of the two group is significant (p<0.001). The mean scoring with SD in group A and group B were 2.68± 2.35 and .36± 1.10 respectively at 14th day difference between the mean score of the group is significant (p<0.001). Conclusion: Topical application of permethrin 5% cream is more effective and safer than oral Ivermectin in the treatment of scabies. TAJ 2020; 33(1): 41-47

EFFECTS OF SYNTHETIC LH/FSH-RELEASING HORMONE (LRH) ON PLASMA LH AND FSH IN AMENORRHOEIC WOMEN

1974 ◽  
Vol 75 (4) ◽  
pp. 647-652 ◽  
Author(s):  
G. Rannevik ◽  
J. Thorell
Keyword(s):  
Urinary Excretion ◽  
Initial Response ◽  
Releasing Hormone ◽  
The Mean ◽  
The Difference ◽  
Serial Measurements

ABSTRACT Eight amenorrhoeic women were given 100 μg synthetic LRH (Hoechst) iv and im, respectively, at an interval of 2 weeks. Four of the women received the iv injection first and four the im injection. The urinary excretion of oestrogens and pregnanediol was low and unaltered throughout the test weeks. The effects of LRH were compared by serial measurements of the plasma LH and FSH during 8 h. The initial response of LH for up to 25 min and that of FSH for up to 60 min were equal whether LRH was given iv or im. The difference appeared later. Four hours after the injection the mean increase of LH to iv injection was 0.5 ng/ml (N. S.), while that to im injection was 1.9 ng/ml (P < 0.01). The corresponding values for FSH were 1.3 (P < 0.05) and 3.2 (P < 0.001). The effect of LRH administration im was thus found to be larger and more prolonged.

Development of Prolonged Delivery of Tramadol and Dissolution Translation by Statistical Data Treatment

2011 ◽  
Vol 4 (1) ◽  
pp. 1331-1337
Author(s):  
P B Parejiya ◽  
B S Barot ◽  
P K Shelat
Keyword(s):  
Drug Release ◽  
Study Data ◽  
Stability Study ◽  
Dissolution Time ◽  
Matrix Tablet ◽  
Burst Effect ◽  
The Matrix ◽  
The Mean ◽  
The Difference ◽  
Dissolution Efficiency

The present study was carried out to fabricate a prolonged design for tramadol using Kollidon SR (Polyvinyl acetate and povidone based matrix retarding polymer). Matrix tablet formulations were prepared by direct compression of Kollidon SR of a varying proportion with a fixed percentage of tramadol. Tablets containing a 1:0.5 (Drug: Kollidon SR) ratio exhibited a rapid rate of drug release with an initial burst effect. Incorporation of more Kollidon SR in the matrix tablet extended the release of drug with subsequent minimization of the burst effect as confirmed by the mean dissolution time, dissolution efficiency and f2 value. Among the formulation batches, a direct relationship was obtained between release rate and the percentage of Kollidon SR used. The formulation showed close resemblance to the commercial product Contramal and compliance with USP specification. The results were explored and explained by the difference of micromeritic characteristics of the polymers and blend of drug with excipients. Insignificant effects of various factors, e.g. pH of dissolution media, ionic strength, speed of paddle were found on the drug release from Kollidon-SR matrix. The formulation followed the Higuchi kinetic model of drug release. Stability study data indicated stable character of Batch T6 after short-term stability study.

Seasonal trends in the stable isotopic composition of snow and meltwater runoff in a subarctic catchment at Okstindan, Norway

2004 ◽  
Vol 35 (2) ◽  
pp. 119-137 ◽  
Author(s):  
S.D. Gurney ◽  
D.S.L. Lawrence
Keyword(s):  
Isotopic Composition ◽  
Mean Value ◽  
Mean Values ◽  
Stable Isotopic Composition ◽  
Meltwater Runoff ◽  
Stable Isotopic ◽  
The Mean ◽  
The Difference ◽  
Δ18o And Δd

Seasonal variations in the stable isotopic composition of snow and meltwater were investigated in a sub-arctic, mountainous, but non-glacial, catchment at Okstindan in northern Norway based on analyses of δ18O and δD. Samples were collected during four field periods (August 1998; April 1999; June 1999 and August 1999) at three sites lying on an altitudinal transect (740–970 m a.s.l.). Snowpack data display an increase in the mean values of δ18O (increasing from a mean value of −13.51 to −11.49‰ between April and August), as well as a decrease in variability through the melt period. Comparison with a regional meteoric water line indicates that the slope of the δ18O–δD line for the snowpacks decreases over the same period, dropping from 7.49 to approximately 6.2.This change points to the role of evaporation in snowpack ablation and is confirmed by the vertical profile of deuterium excess. Snowpack seepage data, although limited, also suggest reduced values of δD, as might be associated with local evaporation during meltwater generation. In general, meltwaters were depleted in δ18O relative to the source snowpack at the peak of the melt (June), but later in the year (August) the difference between the two was not statistically significant. The diurnal pattern of isotopic composition indicates that the most depleted meltwaters coincide with the peak in temperature and, hence, meltwater production.

Study of pumping effect in flow-through electrolysers

1983 ◽  
Vol 48 (8) ◽  
pp. 2232-2248 ◽  
Author(s):  
Ivo Roušar ◽  
Michal Provazník ◽  
Pavel Stuhl
Keyword(s):  
Natural Convection ◽  
Balance Equation ◽  
Volume Fraction ◽  
Industrial Applications ◽  
Pumping Effect ◽  
Flow Through ◽  
The Mean ◽  
The Difference

In electrolysers with recirculation, where a gas is evolved, the pumping of electrolyte from a lower to a higher level can be effected by natural convection due to the difference between the densities of the inlet electrolyte and the gaseous emulsion at the outlet. An accurate balance equation for calculation of the rate of flow of the pumped liquid is derived. An equation for the calculation of the mean volume fraction of bubbles in the space between the electrodes is proposed and verified experimentally on a pilot electrolyser. Two examples of industrial applications are presented.

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