El último baluarte del imperio /

Producto de un trabajo de investigación de varios años sobre un tema clásico de los estudios literarios, la relación ente la emergencia del modernismo, especialmente la obra de Rubén Darío y la recepción de la crítica, sobre todo la española.Este asunto revela un problema más general, el de las relaciones entre América Latina y España, tratado acá sobre el ámbito de lo imaginario.

Co(II) and Cr(III) complexes of formate-formamide mixed ligands: synthesis, structures, single crystal-to-single crystal transformation and magnetic behaviour

Solvothermal treatment of an equimolar mixture of Co(NO3)(2)center dot 6H(2)O, HCONH2 and NaN3 in MeOH at 100 degrees C yielded a three-dimensional NaCl type network Co(HCOO)(2)(HCONH2)(2) center dot HCONH2 (1a) containing formamides in the pores of the structure. Solvated pink 1a undergoes single crystal-to-single crystal (SCSC) transformation at 215 degrees C to form the desolvated dark brown product Co(HCOO)(2)-( HCONH2)(2) (1b) with the retention of the original framework. Reversible single crystal-to-single crystal transformation of 1b (brown) to 1a (pink) in the presence of excess formamide was also established at room temperature. The coordination environment around Co(II) in both 1a and 1b is octahedral with a CoN2O4 coordination composition. A similar reaction replacing Co(II) by Cr(III) produced a heterometallic 3D extended network Na[Cr(HCOO)(4)(HCONH2)(2)]center dot 2H(2)O (2a) at 100 degrees C. An increase in reaction temperature to 150 degrees C produced a simple mononuclear complex Cr(HCOO)(3)(HCONH2)(3) center dot 3H(2)O (2b). Variable temperature magnetic studies revealed the presence of a canting phenomena in both 1a and 1b, and hysteresis loop in the field dependent magnetisation plot at 2 K whereas complex 2a is simply paramagnetic in nature.

Stabilization of diborane(4) by transition metal fragments and a novel metal to pi Dewar-Chatt-Duncanson model of back donation

The feasibility of using transition metal fragments to stabilize B2H4 in planar configuration by donating 2 electrons to the boron moiety is investigated. Building upon the existing theoretical and experimental data and aided by the isolobal analogy, the model transition metal complexes Cr(CO)(4)B2H4 (6), Mn(CO)-CpB2H4 (7), Fe(CO)(3)B2H4 (8) and CoCpB2H4 (9) are chosen to illustrate this unique bonding feature bond strengthening with pi-back donation. Other possible types of complexes with B2H4 and the metal fragment are also explored and the energies are compared. One of the low energy isomers wherein the planar B2H4 interacts with the metal fragment in an in-plane fashion represents a unique case study for the Dewar-Chatt-Duncanson model. In this complex the back-donation from the metal fills the p bonding orbital between the two boron atoms thus forming a B=B double bond.

流动注射分离-原子吸收光谱法测定底泥中生物可利用态Cr(Ⅵ)和Cr(Ⅲ)

湖泊底泥中生物可利用态铬是对湖泊生态环境最有影响的铬赋存形态,分别用弱有机酸或螯合缓冲剂对底泥中生物可利用态铬进行萃取分离。在流动注射系统中,分别以串联在流路中阴、阳离子交换微型柱分离,NH4NO3+抗坏血酸和H2SO4两种洗脱液同时逆向洗脱,实现了对底泥可利用态铬中Cr(Ⅵ)和Cr(Ⅲ)同时在线分离和原子吸收光谱法测定。交换时间2min,洗脱50s,Cr(Ⅵ)和Cr(Ⅲ)回收率分别为85.4%~94.8%和96.7%~106%。本方法对实际样品中不同价态铬进行测定,铬回收率可达95%。Cr(Ⅵ)和Cr(

CR环二极磁铁的磁场优化

FAIR项目中的CR环二极磁铁对磁场积分场的误差分布要求很高,通过削斜与加载镜像板的方法是优化磁场的主要方法,文中介绍了对二极磁铁优化方法和对它的处理方法.利用削斜的方法来改变二极磁铁积分场的误差分布,通过复杂的削斜,已将其高场的误差分布优化到±2×10~(-4).加镜像板的方法主要适合高场,而对低场的调节不明显.另外处理方法的选取对结果的影响也很大,文中对两种方法作了比较.优化模拟计算软件采用的是专门的磁场计算工具OPERA.

The use of half-sandwich iridium dithiolate and diselenolate complexes, Cp*Ir(L)(ER)(2) (L = CO, PMe3, PPh3; ER = SPh, SePh, SeMe), for the synthesis of heterodimetallic compounds. The molecular structure of Cp*Ir(CO)(mu-SePh)(2)[Mo(CO)(4)]

Carbonyl-iridium half-sandwich compounds, Cp*Ir(CO)(EPh)(2) (E = S, Se), were prepared by the photo-induced reaction of Cp*Ir(CO)(2) with the diphenyl dichalcogenides, E2Ph2, and used as neutral chelating ligands in carbonylmetal complexes such as Cp*Ir(CO)(mu-EPh)(2)[Cr(CO)(4)], Cp*Ir(CO)(mu-EPh)(2)[Mo(CO)(4)] and Cp*Ir(CO)(mu-EPh)(2)[Fe(CO)(3)], respectively. A trimethylphosphane - iridium analogue, Cp*Ir(PMe3)(mu-SeMe)(2)[Cr(CO)(4)], was also obtained. The new heterodimetallic complexes were characterized by IR and NMR spectroscopy, and the molecular geometry of Cp*Ir(CO)(mu-SePh)(2)[Mo(CO)(4)] has been determined by a single crystal X-ray structure analysis. According to the long Ir...Mo distance (395.3(1) Angstrom), direct metal-metal interactions appear to be absent. (C) 1998 Elsevier Science S.A. All rights reserved.

Informe de la Segunda Reunión del Grupo de Trabajo sobre Interconexión Eléctrica Nicaragua y Costa Rica, San José, 4-7 marzo 1970: Managua, 26-28 noviembre 1970

Incluye Bibliografía

Stalinismin lyhyt kurssi : Suomalaiset Moskovan Lenin-koulussa 1926-1938

This study of the Finns at the International Lenin School (ILS) reflects history of the Soviet Union during Stalin's era, history of the Communist International (Comintern) as well as history of Finnish communism. The life span of the ILS (1926-1938) matches up with creating and establishing the power structures of Stalinism. Both the ILS and Finnish Communism in the USSR became casualties of the Great Terror (1937-1938). After the WW2, however, the Soviet education was appreciated inside the Communist Party of Finland (CPF). If Finland would have become People's Democracy, the former ILS students would have composed the inner circle of the new "democratic" government. The Finnish teachers of the ILS were leaders of the CPF that was headquartered in Moscow. At the ILS studied in total 141 Finnish communists. The purpose of the ILS was to educate the communist parties' leading stratum of functionaries. They were supposed to internalize current values, methods and discipline of the Bolsheviks. This study evaluates the effects of the total school experience on the Finns that often ended in another total institution in Finland: prison. The curricula of the ILS consisted of theory of Marxism-Leninism, party history, political economics and themes of campaigns of Stalinism. The ILS year included participation in Bolshevik party life and practical work. During summer excursions (praktikas) the students could acquaint themselves with building of socialism in the Soviet Republics. At the ILS, intention to ideological moulding was not hidden. The students were supposed to adopt the Stalinist identity of the professional revolutionaries of the era. The ILS was saturated with ideology and propaganda. This study analyzes especially uses of history as vehicle of ideological standardisation and as instrument of power. Stalin contributed personally to shortcomings of history writing of the communist party. Later he supervised writing of the inclusive handbook of communism, "History of the All-Union Communist Party. Short Course". Special attention will be paid to the effects of Stalin's intervention at the ILS and inside the CPF. The life of the Finns at the ILS and outside the school is described at grass roots. The dividing line between personal and political is analyzed by charting emotional, intimate and bodily experiences of the Finns of the ILS. The fates of the ILS Finns after the studying or teaching period in Moscow are explored in detail. The protagonist among the teachers is Yrjö Sirola that was called "father of the CPF cadres". The Finnish ILS teachers and the formed students that had remained in the USSR were most severely hit by the Great Terror. The Soviet education had most importance in Finland of post WW2 period. The training at the ILS, however, did not contribute to revolution in Finland. The main heading of the study, "A Short Course of Stalinism", crystallises interpretation of the ILS as seat of learning of ideological unity of Stalinism. On the other hand, the title includes a statement of incompleteness of the Stalinist education if the schooling at the ILS had remained in one year.

侧面抽运国产Nd∶YAG陶瓷棒的激光特性

实验研究了激光二极管阵列(LDA)侧向抽运国产Nd∶YAG陶瓷棒的准连续及被动调Q激光输出特性。该陶瓷激光器采用LDA侧面紧密环绕均匀排布的抽运结构,陶瓷棒抽运区域长度为20 mm,其总尺寸为3 mm×35 mm,掺杂原子数分数为~1%。在千赫兹准连续运转条件下,当平-平谐振腔的输出耦合镜透过率为47.3%时,获得最大平均功率23 W的1064 nm激光输出,光束发散角为4.5 mrad,斜率效率达12%。在谐振腔内插入Cr4+∶YAG晶体作为被动调Q开关,成功地实现了陶瓷激光器千赫兹重复频率调Q激光脉冲输出,当Cr4+∶YAG晶体初始透过率为60%时,输出激光脉冲宽度(半峰全宽)可窄至14.5 ns,调Q动静比约为40%。

Synthesis and structural characterization of (pyrazolyl)alkenyl Fischer carbene complexes of chromium and tungsten

Michael addition of substituted pyrazoles 2 to 1-alkynyl Fischer carbene complexes (CO)(5)M=C(OEt)(CdropCPh) (1) (a, M = Cr and b M = W) afforded (pyrazolyl)alkenyl Fischer carbene complexes (CO)(5)M=C(OEt)(CH=C(R(1)R(2)R(3)pz)Ph) (R(1)R(2)R(3)pz = pyrazolyl) 3 (M = Cr) and 4 (M = W), respectively, with an exclusive (E)-configuration in mild to excellent yields. The reaction of la and 3,5-dimethylpyrazole (2b) was monitored to demonstrate the formation and decomposition of complex 3b by H-1 NMR measurements in CDCl3 at 23degreesC. Complexes 3 and 4 were characterized with H-1, C-13{H-1} NMR, IR spectroscopies and elemental analysis. When the substituted pyrazoles were 3-methylpyrazole (2a) and 3,5-di-tert-butylpyrazole (2d), molecular structures of the corresponding (pyrazolyl)alkenyl Fischer carbene complexes 3a and 4d were characterized by X-ray crystallographic study. (C) 2004 Elsevier Ltd. All rights reserved.

Métodos de determinación de parámetros que estiman la disponibilidad de agua-aire en sustratos para plantas y su relación con la respuesta vegetal

Las propiedades físicas e hidráulicas de los sustratos para plantas son las más importantes en relación con la disponibilidad de agua-aire para las raíces. En la Argentina el estudio de sustratos es incipiente y la definición de un protocolo nacional específico es de fundamental importancia para el desarrollo del sector. Como forma de contribución, se propuso como uno de los objetivos, comparar evaluativamente 10 métodos de referencia internacional, para distintos parámetros, sobre perlita (P), 2 turbas (T) y tierra mejorada. Los valores obtenidos resultaron función del método y del sustrato estudiado y no se pudo establecer una equivalencia, en la mayoría de los casos. El método EN13041 resultó el recomendado para una caracterización física completa en el rango 0-100 hPa, mientras que el método utilizando el 'porómetro' diseñado por la NCSU (North Carolina State University) se recomienda para las propiedades físicas en valores próximos a 0-10 hPa. En una segunda parte fueron comparadas las curvas de retención de agua (CR), según 4 métodos de laboratorio en 2 sustratos (80 por ciento P+20 por ciento T; 20 por ciento P+80 por ciento T) con valores in situ en un cultivo de Primula polyantha bajo cubierta. Se midieron potencial agua en hoja y conductancia estomática como forma de evaluar los resultados de los 4 métodos y la modelización de conductividad hidráulica no saturada, en base a los cuales, se diseñaron 4 tratamientos de riego para cada sustrato. No se encontraron diferencias significativas en la respuesta hídrica de las plantas, por lo que se puede decir que los 4 métodos son apropiados de igual forma para el manejo del riego. Cuando se las sometió a tratamiento de sequía se observó una tolerancia diferencial en los individuos, presentando las plantas tolerantes mayor contenido hídrico que las sensibles. Las CR in situ presentaron mayor contenido hídrico que las CR de laboratorio, asociados con la compactación del sustrato y evidenciando el efecto de las raíces. La CR según EN13041 en 20 P+80 T, fue la más cercana a las mediciones in situ, útil para una interpretación agronómica

Novos materiais com polioxotungstatos substituídos com metais d e f

The present work reports studies on the new compounds obtained by the combination of polyoxoanions derived from the Keggin and Lindquist structures with several cations. The studies were first focused on the monolacunary Keggin polyoxoanions [PW11O39M(H2O)]n- (M = FeIII, MnIII and n = 4; M = CoII and n = 5) and its combination with the organic cation 1-butyl-3-methylimidazolium (Bmim+). The association of Bmim+ cation with the polyoxoanion [PW11O39Fe(H2O)]4- allowed to isolate for the first time both the monomeric and the dimeric [PW11O39Fe)2O]10- anions, with the same cation and using simple bench techniques by pH manipulation. Studies regarding the stability of these inorganic species in solution indicated that both species are present in solution in equilibrium. However, the inability to up until now isolate the dimeric unit through simple bench methods, lead to the hypothesis that the cation had a role to play in the selective precipitation of either the monomer or the dimer. Repetition of the same procedures with the polyoxoanions [SiW11O39Fe(H2O)]5- and [PW11O39M(H2O)]n- (M = FeIII, MnIII and n = 4; M = Co and n = 5), afforded only the corresponding monomeric compounds, (Bmim)5[SiW11O39FeIII(H2O)]· 4H2O (3), (Bmim)5[PW11O39CoII(H2O)]· 0.5 H2O, (4) and (Bmim)5[PW11O39MnIII(H2O)]· 0.5 H2O (5). Moreover, the combination of Bmim+ and the polyoxotungstate [PW11O39Co(H2O)]5- afforded two different crystal structures, depending on the synthetic conditions. Thus, a ratio Bmim+:POM of 5:1 and the presence of K+ cations (due to addition of KOH) led to a formula Na2K(Bmim)2[PW11.2O39Co0.8(H2O)]·7H2O (4a), whilst a ratio Bmim:POM of 7:1 led to the formation of a crystal with the chemical formula Na2(Bmim)8[PW11O39Co(H2O)]2·3H2O (4b). Electrochemical studies were performed with carbon paste electrodes modified with BmimCl to investigate the influence of the Bmim+ cation in the performance of the electrodes. The voltametric measurements obtained from solutions containing the anions [PW11O39]7- and [SiW11O39]8- are presented. Results pointed to an improvement of the acquired voltametric signal with a slight addition of BmimCl (up to 2.5% w/w), specially in the studies regarding pH variation. Additional synthesis were carried out with both the cations Omim+ and THTP+.

Poes??a del siglo XX en lengua espa??ola : selecci??n y estudio

En la portada: Consejer??a de Educaci??n, Embajada de Espa??a en Francia

Synthesis, properties, and X-ray crystal and molecular structures of homoleptic alkenyls of tin and chromium

Reaction of Li(CPhCMe2) with SnCl4 or CrCl3·3thf (thf = tetrahydrofuran) affords the isoleptic compounds Sn(CPhCMe2)4 or [Cr(CPhCMe2)4] respectively. The mode of formation and chemical properties are reported for the chromium species, and the structures of the new compounds, both of which have been determined by single-crystal X-ray analysis, are described.