7,457 research outputs found
Liquid phase epitaxy and spectroscopic investigation of optically active KYb(WO4)2 thin layers
In recent years, Yb3+ has attracted much attention as an activating ion because of its small quantum defect for laser emission from 2F5/2 to 2F7/2 at ~1.03 µm, which provides high efficiency and reduced heat generation. A promising material for Yb3+ lasers is KYb(WO4)2 (KYbW) [1]. It can be grown from high-temperature solutions [2]. A suitable substrate material for the growth of single-crystalline layers with thicknesses in the range of the absorption length of ~13 µm at 981 nm is KY(WO4)2 (KYW).\ud
We demonstrate the liquid phase epitaxy (LPE) of KYbW layers at start temperatures as low as 520°C from the chloride solvent KCl-NaCl-CsCl. This temperature is favorable in order to decrease the thermal stresses due to the differences in the thermal expansion coefficients of substrate and layer. Moreover, the choice of [010]-oriented KYW substrates bypasses the large difference in the thermal expansion coefficient along the [010] direction. Our spectroscopic investigations show that the fluorescence lifetime of ~250 µs measured in our LPE-grown KYbW layers is dominated by radiative decay and is very similar to that measured in top-seeded-solution-grown bulk samples [2]. Fast energy migration among the Yb3+ ions and energy transfer to small amounts of Tm3+ and Er3+ ions present in the YbCl3 reagent lead to visible upconversion luminescence in the layers under 981-nm excitation.\ud
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[1] P. Klopp, U. Griebner, V. Petrov, X. Mateos, M.A. Bursukova, M.C. Pujol, R. Solé, J. Gavaldà, M. Aguiló, F. Güell, J. Massons, T. Kirilov, F. Díaz, Appl. Phys. B 2002, 74, 185\ud
[2] M.C. Pujol, M.A. Bursukova, F. Güell, X. Mateos, R. Solé, J. Gavaldà, M. Aguiló, J. Massons, F. Díaz, P. Klopp, U. Griebner, V. Petrov, Phys. Rev. B 2002, 65, 16512
Liquid phase epitaxy and optical investigation of KYb(WO4)2 thin layers
In recent years, Yb3+ has attracted much attention as an activating ion because of its small quantum defect for laser emission from 2F5/2 to 2F7/2 at ~1.03 µm [1], which provides high efficiency and reduced heat generation. Of high practical interest is the thin-disk laser concept [2], which possesses a tremendous advantage over rod lasers because of its axial-cooling approach and consequent weak thermal lensing and good beam quality.\ud
A promising material for Yb3+ thin-disk lasers is KYb(WO4)2 (KYbW) [3]. It can be grown from high-temperature solutions [4]. Nevertheless, the growth of high-quality, single-crystalline layers with thickness in the range of the absorption length of ~13 µm at 981 nm has as yet not been reported. A suitable substrate material is KY(WO4)2 (KYW), but the relatively large differences in the thermal expansion coefficients between KYW and KYbW along the [100], [001], and especially [010] directions [5] favor low temperatures for the hetero-epitaxial growth.\ud
For the first time, we demonstrate liquid phase epitaxy (LPE) of KYbW layers. The layers were grown at start temperatures as low as 520°C, which is favorable in order to decrease the thermal stresses due to the differences in the thermal expansion coefficients of substrate and layer. Moreover, the choice of [010]-oriented substrates bypasses the large difference in the thermal expansion coefficient along the [010] direction. KY1-xYbx(WO4)2 layers with varying x = 0.03-1.00 were grown by LPE. The chloride solvent consisted of the eutectic composition [6] 24.4 mol.% KCl, 30.4 mol.% NaCl, and 42.2 mol.% CsCl. The growth temperature spanned the range from 580 to 500°C and the cooling rate was 0.67-1.00 Kh-1. Crack-free, transparent KYbW layers were grown on (010) substrates.\ud
Spectroscopic investigations have shown that the lifetime of ~250 µs measured in our LPE-grown KYbW layers is dominated by radiative decay and is very similar to that measured in top-seeded-solution-grown bulk samples [4]. Fast energy migration among the Yb3+ ions and energy transfer to small amounts of Tm3+ and Er3+ ions present in the YbCl3 reagent lead to visible upconversion luminescence in the layers under 981-nm excitation.\ud
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[1] T.Y. Fan, IEEE J. Quantum Electron. 29, 1457 (1993).\ud
[2] A. Giesen, H. Hügel, A. Voss, K. Wittig, U. Brauch, H. Opower, Appl. Phys. B 58, 365 (1994).\ud
[3] P. Klopp, U. Griebner, V. Petrov, X. Mateos, M.A. Bursukova, M.C. Pujol, R. Solé, J. Gavaldà, M. Aguiló, F. Güell, J. Massons, T. Kirilov, F. Díaz, Appl. Phys. B 74, 185 (2002).\ud
[4] M.C. Pujol, M.A. Bursukova, F. Güell, X. Mateos, R. Solé, J. Gavaldà, M. Aguiló, J. Massons, F. Díaz, P. Klopp, U. Griebner, V. Petrov, Phys. Rev. B 65, 165121 (2002).\ud
[5] M.C. Pujol, X. Mateos, R. Solé, J. Massons, J. Gavaldà, F. Díaz, M. Aguiló, Mater. Sci. Forum 378-381, 710 (2001).\ud
[6] D. Ehrentraut, M. Pollnau, S. Kück, Appl. Phys. B 75, 59 (2002)
Random Magnetism in Heisenberg Chains with Bond Alternation and Randomness on the Strong Bonds
The Heisenberg chains with bond alternation and randomness on the
strong bonds are studied by the density matrix renormalization group method. It
is assumed that the odd-th bond is antiferromagnetic with strength and
even-th bond can take the values \JA and \JF (\JA > J > 0 > \JF)
randomly. The ground state of this model interpolates between the Haldane and
dimer phases via a randomness dominated intermediate phase. Based on the
scaling of the low energy spectrum and mean field treatment of the interchain
coupling, it is found that the magnetic long range order is induced by
randomness in the intermediate regime. In the magnetization curves, there
appears a plateau at the fractional value of the saturated magnetization. The
fine structures of the magnetization curves and low energy spectrum are
understood based on the cluster picture. The relation with the recent
experiment for (CHCHNHCu(ClBr is discussed.Comment: 6 pages, 7 figures, Final version to appear in J. Phys. Soc. Jp
Site-centered impurities in quantum spin chains
The magnetic behavior of antiferromagnetic spin 1/2 chains with site-centered
impurities in a magnetic field is investigated. The effect of impurities is
implemented by considering different situations of both diagonal and
off-diagonal disorder. The resulting magnetization curves present a wide
variety of plateaux, whose position strongly depends on the kind of disorder
considered. The relevance of these results to experimental situations is also
discussed.Comment: 6 pages, 6 figure
The Syntactic Information in the 'Diccionario Crítico Etimológico Castellano e Hispánico' by J. Corominas and J.A. Pascual as Expressed in the Database 'Syntax.Dbf'
This paper focuses on the structure of a syntactic relational database which includes all the syntactic information contained in the Diccionario Critico Etimológico Castellano e Hispánico, by J . Corominas and J. A. Pascual. Owing to the fact that the dictionary was written in a way which escapes uniformity, it has been necessary to establish a series of fields in order to compile and accommodate the different kinds of knowledge related to the syntactic history of the lexical items. These fields are organized in five groups according to the subject of study: information related to the lemmata; grammatical aspects; syntactic information; other related knowledge; and relevant observations and comments provided by the researchers. Besides reproducing the data given in the dictionary, this type of database comprises severa1 interpretative fields. Therefore, Syntax.dbf constitutes a basic tool for any researcher working on Spanish diachronic syntax.L'objectiu d'aquest article és presentar l'estructura de la base de dades relacional que inclou tota la informació sintictica continguda en el Diccionario Critico Etimológico Castellano e Hispánico de J. Corominas i J. A. Pascual. Tot i que aquest diccionari conté un ampli ventall d'informacions històriques de cadascun dels temes, aquestes no es mostren de forma estructurada, per la qual cosa ha estat necessari estudiar i classificar tots aquells elements relacionats amb aspectes sintàctics. És a partir d'aquest estudi previ que s'han elaborat els diferents camps de la base de dades, els quals s'agrupen en cinc blocs temàtics: informació lemàtica; gramatical; sintàctica; altres aspectes relacionats; i observacions o comentaris rellevants fets per l'investigador. Aquesta base de dades no només reprodueix els continguts del diccionari, sinó que inclou diferents camps interpretatius. Per aquesta raó, Syntax.dbf representa una eina de treball fonamental per a tots aquells investigadors interessats en la sintaxi diacrònica de l'espanyol
The Syntactic Information in the 'Diccionario Crítico Etimológico Castellano e Hispánico' by J. Corominas and J.A. Pascual as Expressed in the Database 'Syntax.Dbf'
L'objectiu d'aquest article és presentar l'estructura de la base de dades relacional que inclou tota la informació sintictica continguda en el Diccionario Critico Etimológico Castellano e Hispánico de J. Corominas i J. A. Pascual. Tot i que aquest diccionari conté un ampli ventall d'informacions històriques de cadascun dels temes, aquestes no es mostren de forma estructurada, per la qual cosa ha estat necessari estudiar i classificar tots aquells elements relacionats amb aspectes sintàctics. És a partir d'aquest estudi previ que s'han elaborat els diferents camps de la base de dades, els quals s'agrupen en cinc blocs temàtics: informació lemàtica; gramatical; sintàctica; altres aspectes relacionats; i observacions o comentaris rellevants fets per l'investigador. Aquesta base de dades no només reprodueix els continguts del diccionari, sinó que inclou diferents camps interpretatius. Per aquesta raó, Syntax.dbf representa una eina de treball fonamental per a tots aquells investigadors interessats en la sintaxi diacrònica de l'espanyol.This paper focuses on the structure of a syntactic relational database which includes all the syntactic information contained in the Diccionario Critico Etimológico Castellano e Hispánico, by J . Corominas and J. A. Pascual. Owing to the fact that the dictionary was written in a way which escapes uniformity, it has been necessary to establish a series of fields in order to compile and accommodate the different kinds of knowledge related to the syntactic history of the lexical items. These fields are organized in five groups according to the subject of study: information related to the lemmata; grammatical aspects; syntactic information; other related knowledge; and relevant observations and comments provided by the researchers. Besides reproducing the data given in the dictionary, this type of database comprises severa1 interpretative fields. Therefore, Syntax.dbf constitutes a basic tool for any researcher working on Spanish diachronic syntax
Ground state and low-lying excitations of the spin-1/2 XXZ model on the kagome lattice at magnetization 1/3
We study the ground state and low-lying excitations of the S=1/2 XXZ
antiferromagnet on the kagome lattice at magnetization one third of the
saturation. An exponential number of non-magnetic states is found below a
magnetic gap. The non-magnetic excitations also have a gap above the ground
state, but it is much smaller than the magnetic gap. This ground state
corresponds to an ordered pattern with resonances in one third of the hexagons.
The spin-spin correlation function is short ranged, but there is long-range
order of valence-bond crystal type.Comment: 2 pages, 1 figure included, to appear in Physica B (proceedings of
SCES'04
Medicamentos e ingestión de alcohol: estudio del almotriptan
Diversos investigadors de l'Hospital Universitari Germans Trias i Pujol i de l'empresa farmacèutica Laboratorios Almirall han dut a terme un estudi per comprovar quin és l'efecte terapèutic de l'almotriptan -un fàrmac utilitzat en el tractament de les crisis de migranya- en relació al consum d'alcohol. Els resultats obtinguts en la recerca indiquen que no és necessari modificar la dosificació del medicament quan s'administra en un pacient en què la crisi de migranya s'ha produït després de la presa d'alcohol.Diversos investigadores del Hospital Universitario Germans Trias i Pujol y de la empresa farmacéutica Laboratorios Almirall han llevado a cabo un estudio para comprobar cuál es el efecto terapéutico del almotriptan - un fármaco utilizado en el tratamiento de las crisis de migraña- en relación al consumo de alcohol. Los resultados obtenidos en la investigación indican que no es necesario modificar la dosificación del medicamento cuando se administra en un paciente en que la crisis de migraña se ha producido después de la ingestión de alcohol
Field Induced Multiple Reentrant Quantum Phase Transitions in Randomly Dimerized Antiferromagnetic S=1/2 Heisenberg Chains
The multiple reentrant quantum phase transitions in the
antiferromagnetic Heisenberg chains with random bond alternation in the
magnetic field are investigated by the density matrix renormalization group
method combined with the interchain mean field approximation. It is assumed
that the odd-th bond is antiferromagnetic with strength and even-th bond
can take the values {\JS} and {\JW} ({\JS} > J > {\JW} > 0) randomly
with probability and , respectively. The pure version ( and
) of this model has a spin gap but exhibits a field induced
antiferromagnetism in the presence of interchain coupling if Zeeman energy due
to the magnetic field exceeds the spin gap. For , the
antiferromagnetism is induced by randomness at small field region where the
ground state is disordered due to the spin gap in the pure case. At the same
time, this model exhibits randomness induced plateaus at several values of
magnetization. The antiferromagnetism is destroyed on the plateaus. As a
consequence, we find a series of reentrant quantum phase transitions between
the transverse antiferromagnetic phases and disordered plateau phases with the
increase of the magnetic field for moderate strength of interchain coupling.
Above the main plateaus, the magnetization curve consists of a series of small
plateaus and the jumps between them, It is also found that the
antiferromagnetism is induced by infinitesimal interchain coupling at the jumps
between the small plateaus. We conclude that this antiferromagnetism is
supported by the mixing of low lying excited states by the staggered interchain
mean field even though the spin correlation function is short ranged in the
ground state of each chain.Comment: 5 pages, 8 figure
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