Second harmonic generation in some donor-acceptor ethylenes—I

We report the absorption spectra, oscillator strengths, ground state and excited state dipole moments, and molecular second order polarizability coefficients (βCT) due to donor—acceptor charge transfer in four trisubstituted ethylenes, namely 1,1-bisdimethylamino-2-nitroethylene, 1,1-bispyrolidino-2-nitroethylene, 1,1-bispiperidino-2-nitroethylene and 1,1-bismorpholino-2-nitroethylene. The results are compared with that of trans-N,N-dimethylamino-nitroethylene, which has a large βCT. The powder second harmonic generation (SHG) intensity of all these molecules is also measured and only 1,1-bispiperidino-2-nitroethylene is found to possess an efficiency of 20% of that of urea under the same conditions. The SHG efficiency of this compound and deficiency in the other molecules in the powdered state is discussed in terms of their arrangements in the unit cell. The crystal structure of the active molecule is also presented and the structure—property relationship is critically examined in all these molecules.

Itsevalikoituminen verkkokyselytutkimuksen haasteena

Internet-yhteyksien käyttö yleistyi Suomessa vuoden 1993 jälkeen, mistä lähtien Internetiä on alettu käyttämään yhä enemmän tiedonkeruun apuvälineenä. Apuvälineenä Internetiä käytetään sekä yhteydenotossa vastaajiin että vastauksien keruussa. Internetin avulla tehtyihin kyselytutkimuksiin liittyy edelleen paljon avoimia metodologisia kysymyksiä. Useimmiten perinteistä, satunnaistettua otoksen keruuta ei voida suorittaa, koska kehikkoperusjoukkoa ei pystytä määrittelemään. Tällöin joudutaan turvautumaan itsevalikoituneeseen verkkotiedonkeruuseen, jossa kyselyä mainostetaan avoimesti tutkimuksen kohteena olevalle ryhmälle ja vastaajat itse päättävät osallistuvatko kyselyyn vai eivät. Samalla Internet-populaation alipeitto voi aiheuttaa harhaa tutkimustuloksiin, jos tavoiteperusjoukkona on jokin suuri populaatio, jossa kaikki eivät käytä Internetiä. Tutkielman tavoite on antaa kuva verkkotiedonkeruun ajanmukaisista menetelmistä sekä erityisesti selvittää itsevalikoituneen verkkotiedonkeruun tilastollista metodologiaa, mahdollisuuksia ja rajoituksia. Tarkoituksena on myös selvittää, kuinka hyvin valikoituneen verkkokyselytutkimuksen harhan korjaaminen onnistuu ajanmukaisilla painotusmenetelmillä. Kyselytutkimusten vastauskadosta sekä valikoituneisuudesta johtuvaa harhaa voidaan korjata painotusmenetelmillä, jos vastauskadon mekanismia tai valikoitumismekanismia pystytään selittämään. Harhaa voidaan korjata sopivien apumuuttujien avulla, jotka korreloivat tulosmuuttujan tai osallistumispäätöksen kanssa. Apumuuttujien tiedot täytyy olla tiedossa sekä kyselyyn osallistujilta että ei-osallistujilta. Perinteisen todennäköisyysotantaan perustuvan aineiston vastauskadosta johtuvaa harhaa korjataan useimmiten jälkiosituspainoilla. Itsevalikoituneen verkkokyselytutkimuksen valikoitumisharhan korjaamiseen on esitetty kaksivaiheista painotusmenetelmää, jonka tarkoituksena on korjata harhaa, joka johtuu Internetin käyttömahdollisuudesta sekä itse osallistumispäätöksestä. Internetin käyttömahdollisuus voidaan mallintaa propensiteettipistemäärän avulla, jonka käänteislukua voidaan käyttää painokertoimena harhan korjaamiseksi. Osallistumispäätöksestä johtuvaa harhaa voidaan korjata tasaamalla aineiston apumuuttujien reunajakaumat vastaamaan populaation reunajakaumia. Tutkimuksessa tarkastellaan kolmea aineistoa. Kelan tutkimusosasto keräsi vuoden 2010 syyskuussa pilotin itsevalikoituneesta verkkokyselytutkimuksesta. Kyselyllä pyrittiin kartoittamaan Suomen 16–80-vuotiaiden kansalaisten yksityisten terveys- ja hammashoitopalvelujen hintatietoja ja tarpeita. Sama kysely lähetettiin myös otosperusteisesti Kelan työntekijöille. Molemmissa kyselyissä vastaukset kerättiin sähköisellä Internet-kyselyllä. Lisäksi tutkielmassa tarkastellaan TNS Gallupin otosperusteisesti Suomen kansalaisilta keräämään suppeampaa puhelinhaastattelukyselyä, jota käytettiin myös itsevalikoituneen aineiston kalibrointiaineistona. Kyselytutkimusaineistojen vastauskatoa korjattiin erilaisilla painotusmenetelmillä, joiden avulla pystyttiin tarkastelemaan kuinka hyvin eri painotusmenetelmät pystyvät korjaamaan valikoitumisesta johtuvaa harhaa. Otosperusteisia verkkokyselytutkimuksia korjattiin jälkiosituspainoilla ja painotuksissa onnistuttiin hyvin, koska aineistossa ei ollut suurta valikoituneisuutta. Itsevalikoituneen verkkokyselytutkimuksen painotuksessa jouduttiin kohtaamaan paljon ongelmia, koska aineisto oli suuresti valikoitunut, ja siinä oli paljon vastauskatoa. Itsevalikoituneen aineiston valikoitumisen harhaa onnistuttiin kuitenkin osaksi korjaamaan, ja osa tulosmuuttujien jakaumatiedoista vastasi lähes otosperusteisen kyselytutkimuksen jakaumatietoja. Tutkimuksen keskeisin tulos oli, että vaikka verkkokyselyn tekeminen on halvempaa ja vähemmän työläämpää kuin otosperusteisen kyselytutkimuksen tekeminen, verkkokyselytutkimuksen suunnitteluun on panostettava entistä enemmän. Itsevalikoituneen verkkokyselytutkimuksen keruussa on suunniteltava tarkemmin kyselyn mainostaminen vastaajaehdokkaille, jotta valikoitumisesta johtuvaa harhaa voidaan paremmin hallita. Tutkimuksessa kävi myös ilmi, että sekä asennetta ja käyttäytymistä kuvaavia kysymyksiä on tärkeä olla kyselytutkimuksissa mukana, koska näiden avulla pystytään selittämään paremmin valikoitumisesta johtuvaa harhaa, kuin pelkästään sosiodemografisten muuttujien avulla.

A note on the choice of interfacial friction angle

Estimates of interfacial friction angle (delta) are necessary for the design of retaining structures and deep foundations, Recommendations in the literature regarding delta values are often contradictory and are therefore not easy to apply in geotechnical design, A critical examination of past studies in terms of data generation techniques used and conclusions drawn indicates that two distinctly different test procedures/techniques have been evolved. The interfacial situation in practice can also be categorized into two broad types, These two types of interface problems in geotechnical engineering are (a) the structure is placed on the free surface of prepared fill (type A situation) and (b) the fill is placed against the material surface which functions as a confined boundary (type B situation), The friction angle delta depends on the surface roughness of the construction material, But in the type A situation, it is independent of density and its limiting maximum value (delta(lim)) is the critical state friction angle phi(cv). In the type B situation, it is dependent on density of the fill and its limiting maximum value is the peak angle of internal friction phi(p) of the fill.

Punching shear strength of flat slab corner column connections .1. Reinforced concrete connections

This paper presents the details of an experimental study on punching shear strength and behaviour of reinforced concrete corner column connections in flat slabs; a quasi-empirical method is proposed for computing the punching shear strength. The method has also been extended for punching shear strength prediction at interior and edge column connections. The test results compare better with the strengths predicted by the proposed method than those by Ingvarson, Zaglool and Pollet available in the literature. Further, the experimental strengths of interior, edge and corner column connections have been compared with the strengths predicted by the proposed method and the two codes of practice, viz. ACI and BS code, to demonstrate the usefulness of the method.

Punching shear strength of flat slab corner column connections .2. Fibre-reinforced concrete connections

This paper gives the details of the studies undertaken to examine the strength and behaviour of fibre-reinforced concrete corner column connections in flat slabs. Tests have been conducted on 16 specimens with varying reinforcement ratio, moment/shear ratio (load eccentricity) and volume fraction of fibres. A quasi-empirical method has been proposed for computing the punching shear strength. The method has also been extended to fibre-reinforced concrete interior column connections, tests on which are available in the literature. The test results have been compared with the strength predicted by the proposed method for corner column as well as interior column connections and a satisfactory agreement noticed.

The log delta log t method for the determination of the coefficient of consolidation

The behaviour of saturated soils undergoing consolidation is very complex, It may not follow Terzaghi's theory over the entire consolidation process, Different soils may behave in such a way as to fit into Terzaghi's theory over some specific stages of the consolidation process (percentage of consolidation), This may be one of the reasons for the difficulties faced by the existing curve-fitting procedures in obtaining the coefficient of consolidation, c(v). It has been shown that the slope of the initial linear portion of the theoretical log U-log T curve is constant over a wider range of degree of consolidation, U, when compared with the other methods in use, This initial well-defined straight line in the log U-log T plot intersects the U = 100% line at T = pi/4, which corresponds to U = 88.3%, The proposed log delta-log t method is based on this observation, which gives the value of c(v) through simple graphical construction, In the proposed method, which is more versatile, identification of the characteristic straight lines is very clear; the intersection of these lines is more precise and the method does not depend upon the initial compression for the determination of c(v).

Secondary compression factor

When the variation of secondary compression, with log(10) t is non-linear, the quantification of secondary settlement through the coefficient of secondary compression, C-alpha epsilon, becomes difficult which frequently leads to an underestimate of the settlement, Log(10) delta - log(10) t representation of such true-compression data has the distinct advantage of exhibiting linear secondary compression behaviour over an appreciably larger time span. The slope of the secondary compression portion of the log(10) e - log(10) t curve expressed as Delta(log e)/(log t) and called the 'secondary compression factor', m, proves to be a better alternative to C-alpha epsilon and the prediction of secondary settlement is improved.

Collapse behaviour of a residual soil

Residually derived red soils occur in Bangalore District of Karnataka State, India. The porous and unsaturated nature of the red soils makes them susceptible to collapse on wetting under load. The present study analyses the collapse behaviour of an unsaturated bonded (undisturbed) red soil from Bangalore referenced to tests on samples in an unbonded (remoulded) state. A filter paper method was used to determine the matric suction of the bonded and unbonded specimens, and mercury intrusion porosimetry (MIP) was used to determine their soil structure. Analysis of the experimental results shows that bonding plays an important role in the collapse behaviour of the unsaturated residual soil. The results of the study also provide insight into the volume change behaviour of unsaturated bonded soils on wetting within and beyond the yield locus.

Seismic bearing capacity factors for spread foundations

The effect of horizontal earthquake body forces on the bearing capacity of foundations has been examined computationally in a rigorous manner by employing the method of stress characteristics. The bearing capacity factors N-c, N-q and N-y, due to the components of soil cohesion, ground surcharge pressure and soil unit weight respectively, have been plotted as a function of earthquake acceleration coefficient (a(h)) for different values of soil friction angle (phi). The inclusion of earthquake body forces causes a considerable reduction in the bearing capacity factors. The bearing capacity factors N-c and N-q are seen to be approximately of the same magnitude as those reported in the literature on the basis of different solution methods. However, the obtained values of N-y are found to be significantly smaller than the available results. The nature of the pressure distribution along the footing base and the geometry of the observed failure patterns vary with the consideration of earthquake body forces.

Swelling pressure of sodium montmorillonites

Determination of the swelling pressure of montmorillonitic clays is required in many situations concerned with stability problems of foundations, retaining walls, slope stability of embankments and excavations in expansive soils. Recently expansive soils such as bentonite have been used as a mixture backfill material, for example as backfill material for nuclear waste disposal systems, for which a knowledge of the swelling pressure is desirable. This is the pressure required to keep the clay-water system at the required void ratio when it is allowed to absorb water or electrolyte. If the pressure is less than the swelling pressure, volume expansion occurs; if the pressure is more than the swelling pressure, volume compression occurs. Because of isomorphous substitutions in the crystal lattice, in general the clay particles carry negative charges at the surfaces of the platelets. Exchangeable cations in the clay media are attracted to these negative charges, but this attraction is opposed by the tendency of ions to be distributed. As a result, an electric diffuse double layer is formed (Gouy, 1910).

Dynamic properties of sand from dry to fully saturated states

By using bender and extender elements test, the velocities of the primary and shear waves, V(P) and V(s) respectively, were measured for a sandy material by gradually varying the degree of saturation, S(r), between the dry and fully saturated states. The effect on the results of varying the relative density and effective confining pressure was also studied. The measurements clearly reveal that for a certain optimum S(r), which is around 0.7-0.9% for the chosen sand, the value of the shear modulus G reaches a maximum value, whereas the corresponding Poisson's ratio nu attains a minimum value. The values of the shear modulus corresponding to S(r) approximate to 0% and S(r) = 100% tend towards the same value. For values of Skempton's B parameter greater than 0.99, the values of V(P) and nu rise very sharply to those of water. The predictions from Biot's theory with respect to the variation of V(P) with S(r) match well with the measured experimental data.

Seismic reliability assessment of internal stability of reinforced soil walls using the pseudo-dynamic method

The study focuses on probabilistic assessment of the internal seismic stability of reinforced soil structures (RSS) subjected to earthquake loading in the framework of the pseudo-dynamic method. In the literature, the pseudo-static approach has been used to compute reliability indices against the tension and pullout failure modes, and the real dynamic nature of earthquake accelerations cannot be considered. The work presented in this paper makes use of the horizontal and vertical sinusoidal accelerations, amplification of vibrations, shear wave and primary wave velocities and time period. This approach is applied to quantify the influence of the backfill properties, geosynthetic reinforcement and characteristics of earthquake ground motions on reliability indices in relation to the tension and pullout failure modes. Seismic reliability indices at different levels of geosynthetic layers are determined for different magnitudes of seismic acceleration, soil amplification, shear wave and primary wave velocities. The results are compared with the pseudo-static method, and the significance of the present methodology for designing reinforced soil structures is discussed.

Prioritisation of micro-catchments based on morphology

Two multicriterion decision-making methods, namely `compromise programming' and the `technique for order preference by similarity to an ideal solution' are employed to prioritise 22 micro-catchments (A1 to A22) of Kherthal catchment, Rajasthan, India and comparative analysis is performed using the compound parameter approach. Seven criteria - drainage density, bifurcation ratio, stream frequency, form factor, elongation ratio, circulatory ratio and texture ratio - are chosen for the evaluation. The entropy method is employed to estimate weights or relative importance of the criterion which ultimately affects the ranking pattern or prioritisation of micro-catchments. Spearman rank correlation coefficients are estimated to measure the extent to which the ranks obtained are correlated. Based on the average ranking approach supported by sensitivity analysis, micro-catchments A6, A10, A3 are preferred (owing to their low ranking) for further improvements with suitable conservation and management practices, and other micro-catchments can be processed accordingly at a later phase on a priority basis. It is concluded that the present approach can be explored for other similar situations with appropriate modifications.