Possible thermal structure of the eastern part of the Central Alps

Summary This is a survey of the trend of temperature in respect of depth in the lithosphere under the eastern part of the Central Alps between Innsbruck and Graz, using a geothermal model based on the reduced heat production along the vertical and on the thermal, conductivity dependence upon temperature and pressure. A linear relationship has been found between the reduced heat flow and the mean surface heat flow; it was thus possible to estimate the radiogenic heat flow produced by the sialic crust and the heat flow entering its base. The geotherm corresponding to the surface heat flow in combination with the melting point curves of granitic and gabbroic rocks and with the mantle solidus was used to explain the observed low-velocity zones in the crust and to determine the depth of the lithosphere-asthenosphere transition.

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Riassunto Si studia l'andamento della temperatura con la profondità nella litosfera sotto il settore orientale delle Alpi Centrali, compreso tra Innsbruck e Graz, per mezzo di un modello geotermico che tiene conto della diminuzione di produzione di calore lungo la verticale e della dipendenza della conducibilità termica dalla temperatura e dalla pressione. Si è trovata una relazione lineare tra il flusso di calore ridotto e quello medio alla super-ficie, che ha permesso di stimare il flusso di calore radiogenico prodotto dalla crosta sialica e quello entrante alla sua base. La geoterma corrispondente al flusso di calore superficiale è stata confrontata con le curve di fusione di rocce granitiche e gabbriche e con il solidus del mantello, per spiegare le zone crostali a bassa velocità e per determinare la profondità del confine litosfera-astenosfera.

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Резюме Используя геотермальную модель, основанную на уменьшении выделения тепла вдоль вертикали и на зависимости удельной теплопроводности от температуры и давления, анализируется распределение температур по глубине в литосфере под восточной частью центральных Альп между Иннсбруком и Грацем. Получено линейное соотношение между потоком приведенного тепла и средним потоком тепла с поверхности. Таким образом, можно оценить радиоактивный поток тепла из земной коры и поток тепла, входящий в основание. Геотерма, соответствующая потоку поверхностного тепла, сравнивается с кривыми плавления гранитных и вулканических пород и криавой твердой мантии, чтобы обьяснить зоны с малыми скоростями в земной коре и определить глубину границы между литосферой и астеносферой.

     

Vertical crustal movements in the Messina area

Summary After briefly analysing the geological and geodynamic structure of the Strait of Messina area, its faults and its intense seismic activity, the results of high-precision spirit levelling carried out before and after the 1908 earthquake are reviewed together with the measurements carried out by the Istituto Geografico Militare during 1967 and 1970–1971. These results are then compared with the results of a high-precision levelling survey carried out in 1981 in the metropolitan area of Messina as the first part of a global survey in progress in the whole zone of the Strait. The comparison shows strong agreement in the trend of the coseismic slip following the 1908 event and the aseismic slip in the 1967–1970 and 1970–1981 periods.

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Riassunto Dopo una breve analisi della struttura geologica e geodinamica dell'area dello stretto di Messina, delle faglie presenti e della sua intensa attività sismica, si fanno alcune considerazioni sui risultati di livellazioni geometriche effettuate prima e dopo il terremoto del 1908 e quelli relativi alle misure eseguite dall'Istituto Geografico Militare negli anni 1967 e 1970–1971. Si riportano quindi i risultati di una campagna di livellazione geometrica effettuate nell'area cittadina di Messina quale primo tratto di una rete di piú ampio sviluppo previsto su tutta l'area dello stretto. L'analisi dei dati mostra un buon accordo con l'andamento dello scorrimento cosismico seguito all'evento del 1908 e quello asismico nel periodo 1967–1970.

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Резюме После анализа геологической и геодинамической структуры пролива в районе Мессина, его дефектов и интенсивности сейсмической активности, проводится обзор результатов измерений, проведенных до и после землетрясения 1908 года, и результатов измерений, проведенных Военным Географическим Институтом в 1967 г. и 1970–71 г.г. Эти результаты затем сравниваются с результатами исследований уровня, проведенными в 1981 г. в районе Мессины. Сравнение обнаруживает удовлетворительное согласие с тенденцией сейсмического скольжения после события 1908 г.

     

A passive solar heater-refrigerator

Summary In this paper we study the nonequilibrium thermodynamic steady-state behaviour of a model system representing a core surrounded by an envelope in which the envelope interacts with the solar radiation and with an external bath having a given temperature profile. The heat flow between core and envelope can be controlled by varying the thermal conductivity of their interface. We show that this system acts as a passive heat pump raising the core average temperature with respect to the average equilibrium value corresponding to a fixed value of the interface conductivity, at the same time flattening its oscillation in time. By changing the time dependence of the conductivity the systemvice versa acts as a refrigerator. We show how the limits of this performance depend on the passive parameters such as surfaces, conductivities, heat capacities. The periodicity considered in this study is the daily cycle.

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Riassunto In questo lavoro si studia lo stato stazionario di non equilibrio termodinamico per un sistema che rappresenta modellisticamente un corpo circondato da un involucro; questo interagisce con la radiazione solare e con un bagno termico esterno caratterizzato da una temperatura che dipende dal tempo in modo prefissato. Il flusso di calore fra l'interno e l'involucro è controllato variando la conducibilità termica dell'interfaccia. Noi mostriamo che questo sistema funziona come una pompa di calore passiva, cioè innalza la temperatura media dell'interno rispetto a quella che si avrebbe nel caso di conducibilità fissa e, allo stesso tempo, riduce le oscillazioni di codesta temperatura. Semplicemente cambiando la dipendenza oraria del controllo, il sistema funziona come un frigorifero. Si mostra in che modo tale effetto dipenda dai parametri passivi che sono le superfici, i calori specifici, la conducibilità. Consideriamo in questo studio il ciclo giornaliero.

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Резюме В этой работе мы исследуем неравновесное термодинамическое стационарное поведение модельной системы, представляющей ядро, окруженное оболочкой, которая взаимодействует с солнечным излучением и с внешним термостатом, имейщим заданный профиль температур. Поток тепла между ядром и оболочкой можно контролировать посредством изменения теплопровдности их границы раздела. Мы покзываем, что эта система действует, как пассивный тепловой насос, поднимающий среднюю температуру ядра относительно средней равновесной величины, соответствующей фиксировчнной величине теплопроводности границе раздела, и в то же время сглаживающий осцилляции температуры во времени. Изменяя временную зависимость теплопроводности, описанная система может действовать как холодильник. Мы показываем, как указанный эффект зависит от таких пассивных параметров, как поверхности, проводимости, теплоемкости. Периодичность рассмотренной системы представляет суточный цикл.

     

Maximum irreversible availability for continuous systems

Summary In this paper we generalize the study of the irreversible availability, already widely developed for discrete systems, to field theory. We derive the general equations and solve analytically the stationary unidimensional case.

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Riassunto In questo articolo si generalizza lo studio del lavoro estraibile di Gibbs, che è già ampiamente sviluppato nel caso dei sistemi discreti, al formalismo della teoria continua di campo. Si formulano le equazioni differenziali in generale e si risolve analiticamente il caso del problema unidimensionale stazionario.

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Резюме В зтой работе мы обобщаем исследование необратимой доступности, развитое для дискретных систем, для формализма непрерывной теории поля. Мы выводим общие уравнения и решаем аналитически проблему в стационарном одномерном случае.

     

On the estimate of the mechanical power that can be processed by the earth

Summary The Earth is a finite system closed with respect to mass and open with respect to energy, the in and out radiation fluxes. Due to the symmetry of the body and the periodicity of the incoming-energy driving term it is presumable that the circulation of mass and heat is a very complex but steady state. This is a nonuniform state or a far from thermodynamic equilibrium state; as such the question arises of what is the availability or maximum mechanical work that can be extracted from this system. We formulate, the concept of efficiency for a complex nonequilibrium system and find approximate evaluations from two simplified models in which the wind circulation is neglected.

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Riassunto La Terra è un sistema finito, chiuso rispetto alla massa e aperto rispetto all'energia, i flussi di radiazione entrante e uscente. A causa della simmetria sferica e della periodicità del flusso entrante si presume che la circolazione di energia termica sulla Terra formi, per quanto complesso, uno stato stazionario. Questo è uno stato non uniforme, cioè lontano dall'equilibrio termodinamico quindi è logico chiedersi qual'è il lavoro ideale massimo che può essere estratto da un tale sistema. Si formula il concetto di efficienza meccanica per un sistema complesso in non equilibrio e si trovano valutazioni approssimate per due modelli nei quali la circolazione del vento è trascurata.

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Резюме Земля представляет конечную систему, замкнутую относительно массь и открытую относительно энергии и падающих и выходящих потоков. В силу сферической симметрии Земли и периодичности падающей энергии предполагается, что циркуляция тепловой энергии представляет очень сложное, но стационарное состояние. Это состoояние является неоднородным, т. е. далеко от состояния термодинамического равновесия, поэтому возникает естественный вопрос, какая максимальная механическая работа может быть получена из этой системы. Мы формулируем концепцию эффективности для сложной неравновесной системы и получаем приближенные оценки из двух упрощенных моделей, в которых не учитывается пиркуяция ветра.

     

Quantum diffusion in polaron model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers

We numerically investigate quantum diffusion of an electron in a model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers with fluctuation of the parameters due to the impact of colored noise. The randomness is introduced by fluctuations of distance between two consecutive bases along the stacked base pairs. We demonstrate that in the model the decay time of the correlation can control the spread of the electronic wavepacket. Furthermore it is shown that in a motional narrowing regime the averaging over fluctuation causes ballistic propagation of the wavepacket, and in the adiabatic regime the electronic states are affected by localization.     

Ab initio study of phonons and structural stabilities of the perovskite-type MgSi{O_3}

Using the local-density approximation, calculating the Hellmann-Feynman forces, applying the direct method and deriving the phonon dispersion relations, the stability of the perovskite-like structures of MgSiO₃ at T =0 have been studied. The cubic Pmm phase shows a dispersion-less soft phonon branch spreading from the R to M points of the cubic Brillouin zone. This soft branch persists up to high pressures of 150 GPa. The low-symmetry phases I4/mcm and Imma, P4/mbm can be considered as a result of the soft mode condensation at the M and R points, respectively. These phases prove to be unstable at T =0. The experimentally observed Pmnb phase is a consequence of the intersection of Imma and P4/mbm space groups. Thus, it can be regarded as a simultaneous condensation of two soft modes: one at the M and a second at the R high-symmetry points of the cubic Brillouin zone. The phonon dispersion relations of Pmnb show that this phase is stable and its optical phonons appear above 4.0 THz only. Received 15 October 1999 and Received in final form 14 January 2000     

Localization properties of electronic states in a polaron model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers

We numerically investigate localization properties of electronic states in a static model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers with realistic parameters obtained by quantum-chemical calculation. The randomness in the on-site energies caused by the electron-phonon coupling is completely correlated to the off-diagonal parts. In the single electron model, the effect of the hydrogen-bond stretchings, the twist angles between the base pairs and the finite system size effects on the energy dependence of the localization length and on the Lyapunov exponent are given. The localization length is reduced by the influence of the fluctuations in the hydrogen bond stretchings. It is also shown that the helical twist angle affects the localization length in the poly(dG)-poly(dC) DNA polymer more strongly than in the poly(dA)-poly(dT) one. Furthermore, we show resonance structures in the energy dependence of the localization length when the system size is relatively small.     

(CdSe)n(n=1,2)团簇性质及CdSe分子热力学性质的理论计算

用密度泛函B3LYP方法、有效核势(ECP)基组LanL2DZ对(CaSe)n(n=1,2)团簇进行了理论研究,得到(CaSe)n(n=1,2)分子体系可能存在的状态及各电子状态的平衡几何Re、谐振频率、偶极矩和离解能De、不同温度、压力下的热力学函数值;设用总能量中的电子和振动能量近似代表CdSe分子处于固态时的能量,用总熵中的电子和振动熵近似代表CdSe分子处于固态时的熵,进而计算了Cd与Se反应的△Hθ、△Sθ、△G,并由此计算出不同温度的反应平衡常数Kp结果表明:在298～1400K温度范围内,Cd与Se反应的自由能值均为负,且随着温度的升高,△Gθ值负的越多,表明在这个温度范围内反应能自发发生,而且自发趋势随温度的升高逐渐增大;平衡常数逐渐减小,即反应进行程度随温度的升高逐渐减小;CdSe分子材料的导电性随压力增大而增强.     

在Pd/Cu(100)表面上外延的超薄Co膜的结构和磁性

利用脉冲激光溅射(PLD)和分子束外延(MBE)方法制备了超薄膜系统 Co/Pd/Cu(100).脉冲激 光溅射生长的单原子Pd层呈现了很好的二维生长模式.在这个Pd表面上，分子束外延生长的C o层直至12个原子层都表现了层-层生长模式.利用俄歇电子谱(AES)和低能电子衍射(LEED)研 究了该系统的表面结构.利用低温磁光克效应(MOKE)研究了系统的磁学性质.结构研究表明， Co层由于面内晶格失配应力而具有一个四方正交结构；与对比样品Co/Cu(100)的比较研究说 明Pd层的存在强烈地改善了Co膜的起始生长模式和结构.磁光克效应测量表明，Pd层的存在 改变了Co层的磁学性质. 关键词： 薄膜的磁性质 组织与形貌 界面磁性     

(HgSe)_n(n=1～6)团簇结构和性质的密度泛函研究

本工作采用LANL2DZ赝势基组、B3LYP方法对(HgSe)n(n=1~6)团簇进行了结构优化、自然键原子轨道和频率计算,得到(HgSe)n(n=1~6)团簇基态的平衡几何结构、电子状态、垂直电离势、垂直电子亲和势、偶极矩、三个基本热力学函数等相关性质,并系统分析了该团簇的几何构型、原子净电荷布局、前沿分子轨道特征.结果表明:基态稳定结构(HgSe)2为平面四边形,(HgSe)n(n=3~6)为笼状结构,且稳定顺序为(HgSe)5(HgSe)4(HgSe)6(HgSe)2HgSe(HgSe)3,极性顺序为:(HgSe)4HgSe(HgSe)3(HgSe)5(HgSe)6(HgSe)2,(HgSe)6和(HgSe)2分子空间结构的对称性较好.(HgSe)n(n=1~6)团簇各体系都有较好的电子供体及受体等活性部位,随着n增大轨道离域现象明显,利于电子的转移,导电性增强.     

(HgSe)n(n=1~6)团簇结构和性质的密度泛函研究

本工作采用LANL2DZ赝势基组、B3LYP方法对(HgSe)n(n=1~6)团簇进行了结构优化、自然键原子轨道和频率计算,得到(HgSe)n(n=1~6)团簇基态的平衡几何结构、电子状态、垂直电离势、垂直电子亲和势、偶极矩、三个基本热力学函数等相关性质,并系统分析了该团簇的几何构型、原子的净电荷布局、前沿分子轨道特征。结果表明：基态稳定结构(HgSe)2为平面四边形,(HgSe)n(n=3~6)为笼状结构,且稳定顺序为(HgSe)5>(HgSe)4>(HgSe)6>(HgSe)2>HgSe>(HgSe)3,极性顺序为：(HgSe)4>HgSe>(HgSe)3>(HgSe)5>(HgSe)6>(HgSe)2,(HgSe)6、(HgSe)2分子空间结构的对称性较好。(HgSe)n(n=1~6)团簇各体系都有较好的电子供体及受体等活性部位,随着n增大轨道离域现象明显,利于电子的转移,导电性增强。     

(BN)25团簇的结构与性能

采用密度泛函理论的杂化密度泛函（B3LYP）方法,在6-31G （d）基组水平上,对（BN）₂₅团簇进行结构优化和频率计算,得到基态构型,并对其稳定性、自然键轨道（NBO）、振动光谱和NICS进行计算.结果表明：（BN）₂₅团簇的能隙值较高,具有良好的化学稳定性;B原子和N原子的内部及原子之间都会发生s、p轨道杂化,原子之间有少量电荷转移;（BN）₂₅团簇的红外光谱和拉曼光谱都有较多振动峰;（BN）₂₅团簇具有芳香性.     

Optical and electronic properties of (GaAs)n / (InAs)n(001) superlattices: LMTO-ASA approach

The optical and electronic properties of (GaAs)_n/(InAs)_n superlattices are calculated by means of LMTO-ASA method. The too small band gap problem of bulk material and superlattices is corrected by adding to the effective potentials an additional external potential that is sharply peaked at the atomic sites. The results show that the optical properties of GaAs/InAs(001) superlattices are about average of that of two bulks of GaAs and InAs.     

First-principles investigations of the physical properties of RCd (R=Ce,La, Pr,Nd)

The crystal structural, electronic, elastic and the thermodynamic properties of RCd are investigated by using the first-principles plane-wave pseudopotential density function theory within the generalized gradient approximation (GGA). The calculated equilibrium lattice parameters for RCd are in good agreement with the available experimental data. Furthermore, the optical properties, namely the dielectric function, refractive index and electron energy loss are reported for radiation up to 30 eV. Finally, the elastic properties, the bulk modulus and the Debye temperature of RCd are given for reference.     

Transport and magnetoresistance effect in an oxygen-deficient SrTiO_3/La_(0.67)Sr_(0.33)MnO_3 heterojunction

An oxygen-deficient SrTiO3/La0.67Sr0.33MnO3 heterojunction is fabricated on an SrTiO3 （001） substrate by a pulsed laser deposition method. The electrical characteristics of the heterojunction are studied systematically in a temperature range from 80 K to 300 K. The transport mechanism follows I ∝ exp （eV/nkT） under small forward bias, while it becomes space charge limited and follows I ∝ Vm（T） with 1.49〈 m 〈1.99 under high bias. Such a heterojunction also exhibits magnetoresistance （MR） effect. The absolute value of negative MR monotonically increases with temperature decreasing and reaches 26.7% at 80 K under H=0.7 T. Various factors, such as strain and oxygen deficiency play dominant roles in the characteristics.     

Electromagnetic cascade showers with the LPM effect in standard rock initiated by extremely high-energy (1015 eV to 1021 eV) gamma-rays

Summary High-energy neutrinos produce finally high-energy electromagnetic cascade showers. For the detectio of high-energy neutrinos, it is necessary to examine the behaviour of the electromagnetic cascade showers in the higher-energy region. It is well known that the LPM effect plays a decisive role in the electromagnetic cascade shower development at higher energies. In the present paper, the behaviour of electromagnetic cascade showers including the LPM effect (LPM showers) in standard rock is examined using the calculational technique developed by Fujimaki and Misaki. In order to clarify the characteristics of LPM showers, similar calculations are also carried out for cascade showers in the absence of the LPM effect (BH showers). Comparisons between the two different kinds of cascade showers are made over electron transition curves, track lengths and fractional dissipated energies. Finally, the strong deviation of LPM showers from the normal BH showers is emphasized.     

Measurements of sound velocity of laser-irradiated iron foils relevant to Earth core condition

We present a novel scheme to measure sound velocity of shock-compressed iron of geophysical interest. The sound velocity of laser-irradiated iron foils was obtained with side-on X-ray radiograph technique from measured rarefaction wave velocity of shocked iron. Iron foils were irradiated with a two-stepped square laser pulse to reach Earth's core condition by double compression. The experimental parameters of temperature and pressure were very close to the Earth's core condition.     

Piezoelectric activity and phase transitions in (PMN)0.69(PT)0.31 single crystal

Piezoelectric and dielectric investigations have been performed on a (PMN)_0.69(PT)_0.31 single crystal. Low frequency (100?Hz) dielectric permittivity measurements revealed distinct anomaly at 129°C (T _εmax) corresponding to the structural transformation from the tetragonal to cubic phase. Two other anomalies have been detected at 90 and 96°C. After preliminary polarization in the d.c. electric field, switched on above T _εmax and switched off inside the tetragonal phase, the piezoelectric activity has been observed in function of temperature. Values of the piezoelectric resonance frequencies changed markedly at 96°C (on cooling) and 124°C (on heating) showing clear softening of the elastic properties near these temperatures. Values of the piezoelectric and electromechanical coupling coefficients obtained were respectively of the order of 800?pCN^?1 (d ₃₁) and 0.35?(k ₃₁). Piezoelectric activity was detected tens of degrees above the temperature T _εmax and disappeared at temperature at which the dispersion of the dielectric permittivity due to the presence of polar nanoregions is negligible. It was found that strong softening of the elastic properties accompanies phase transitions to the tetragonal and monoclinic phase.     

Magnetic properties of 57Fe/Ir(100) superlattices

Summary The synthesis of a new BCT Fe phase was performed in Fe/Ir(100) superlattices grown by MBE. Magnetic properties of⁵⁷Fe/Ir(100) superlattices with 4 ml Fe and variable Ir thickness (2–30 ?) are investigated by⁵⁷Fe conversion electron M?ssbauer spectroscopy in the 4.2–300 K temperature range. Two spectral components are evidence, related, respectively, to Fe atoms involved in the central part of the iron layers and at the interface between iron and iridium layers. The appearance of a high magnetic hyperfine splitting in the iron BCT structure above a volume threshold of 12 ?³ is evidenced. Marked differences are observed between the mean magnetic properties and the local ones suggesting strong relaxation effects. Paper presented at ICAME-95, Rimini, 10–16 September 1995.