Extent and limitations of density functional theory in describing magnetic systems

The performance of density-functional theory to solve the exact, nonrelativistic, many-electron problem for magnetic systems has been explored in a new implementation imposing space and spin symmetry constraints, as in ab initio wave function theory. Calculations on selected systems representative of organic diradicals, molecular magnets and antiferromagnetic solids carried out with and without these constraints lead to contradictory results, which provide numerical illustration on this usually obviated problem. It is concluded that the present exchange-correlation functionals provide reasonable numerical results although for the wrong physical reasons, thus evidencing the need for continued search for more accurate expressions.

Space and momentum representation analysis of Hartman's effect in wave packet transmission

The Hartman effect is analyzed in both the position and momentum representations of the problem. The importance of Wigner tunneling and deep tunneling is singled out. It is shown quantitatively how the barrier acts as a filter for low momenta (quantum speed up) as the width increases, and a detailed mechanism is proposed. Superluminal transmission is also discussed.

Spontaneous mirror symmetry breaking in the limited enantioselective autocatalysis model: abyssal hydrotermal vents as scenario for the emergence of chirality in prebiotic chemistry

The emergence of chirality in enantioselective autocatalysis for compounds unable to transform according to the Frank-like reaction network is discussed with respect to the controversial limited enantioselectivity (LES) model composed of coupled enantioselective and non-enantioselective autocatalyses. The LES model cannot lead to spontaneous mirror symmetry breaking (SMSB) either in closed systems with a homogeneous temperature distribution or in closed systems with a stationary non-uniform temperature distribution. However, simulations of chemical kinetics in a two-compartment model demonstrate that SMSB may occur if both autocatalytic reactions are spatially separated at different temperatures in different compartments but coupled under the action of a continuous internal flow. In such conditions, the system can evolve, for certain reaction and system parameters, toward a chiral stationary state; that is, the system is able to reach a bifurcation point leading to SMSB. Numerical simulations in which reasonable chemical parameters have been used suggest that an ade- quate scenario for such a SMSB would be that of abyssal hydrothermal vents, by virtue of the typical temper- ature gradients found there and the role of inorganic solids mediating chemical reactions in an enzyme-like role. Key Words: Homochirality Prebiotic chemistry.

Polyconductivity in polypyrrole: the correlated electron glass

p-toluensulfonate doped polypyrrole ~PPy!, undergoes an electric-field induced reversible transition from an insulating state to a highly conductive one. The spatially average field can be as small as 200 V/cm, when the temperature of the sample is below 20 K. The applied electric field leads to a sharp jump in the value of the current to a value which is nearly five orders of magnitude higher than before. When the applied electric field is reduced to below a critical value, the system switches back to a low conductive state. The effect is reversible, symmetric in voltage, and reproducible for different samples. The switching is, we believe, an electronic glass melting transition and it is due to the disordered, highly charged granular nature of PPy.

Polyconductivity in polypyrrole: The correlated electron gas

p-toluensulfonate doped polypyrrole (PPy), undergoes an electric-field induced reversible transition from an insulating state to a highly conductive one. The spatially average field can be as small as 200 V/cm, when the temperature of the sample is below 20 K. The applied electric field leads to a sharp jump in the value of the current to a value which is nearly five orders of magnitude higher than before. When the applied electric field is reduced to below a critical value, the system switches back to a low conductive state. The effect is reversible, symmetric in voltage, and reproducible for different samples. The switching is, we believe, an electronic glass melting transition and it is due to the disordered, highly charged granular nature of PPy.

Extent and limitations of density functional theory in describing magnetic systems

The performance of density-functional theory to solve the exact, nonrelativistic, many-electron problem for magnetic systems has been explored in a new implementation imposing space and spin symmetry constraints, as in ab initio wave function theory. Calculations on selected systems representative of organic diradicals, molecular magnets and antiferromagnetic solids carried out with and without these constraints lead to contradictory results, which provide numerical illustration on this usually obviated problem. It is concluded that the present exchange-correlation functionals provide reasonable numerical results although for the wrong physical reasons, thus evidencing the need for continued search for more accurate expressions.

Chiroptical measurement of chiral aggregates at liquid-liquid interface in centrifugal liquid membrane cell by Mueller matrix and conventional circular dichroism methods

The centrifugal liquid membrane (CLM) cell has been utilized for chiroptical studies of liquid-liquid interfaces with a conventional circular dichroism (CD) spectropolarimeter. These studies required the characterization of optical properties of the rotating cylindrical CLM glass cell, which was used under the high speed rotation. In the present study, we have measured the circular and linear dichroism (CD and LD) spectra and the circular and linear birefringence (CB and LB) spectra of the CLM cell itself as well as those of porphyrine aggregates formed at the liquid-liquid interface in the CLM cell, applying Mueller matrix measurement method. From the results, it was confirmed that the CLM-CD spectra of the interfacial porphyrin aggregates observed by a conventional CD spectropolarimeter should be correct irrespective of LD and LB signals in the CLM cell.

L'Acadèmia d'Estudiants de medicina : Barcelona, 1845-1850

Amb aquest treball es dona testimoni de l'existència i activitats de l'Acadèmia d'Estudiants de Medicina entre els anys 1845 i 1850, una associació que agrupava els estudiants dels dos últims anys de Medicina. A més a més, els autors fan una descricpció acurada del marc acadèmic per a l'estudi de la medicina en aquella època: el funcionament de la facultat, el nombre de catedràtics, professors i alumnes, les instal·lacions, etc. El treball conté també un registre de les sessions acadèmiques (a raó d'una per setmana) cel·lebrades de les què es guarda referència. Ja per últim, s'inclouen a l'addenda, tres memòries amb tres dissertacions de mans d'Eliseu Forest i Cardona, Antoni de la Creu Roca i Flaquer i Francesc Sunyer i Capdevila.

Orígens del Col·legi Oficial de Metges de Barcelona

El present llibre pretèn ésser una aproximació analítica d'uns fets històrics que a la darreria del segle XIX i començament del XX van commoure a les professions sanitàries. Concretament es parla de la problemàtica que va suposar la creació i posada en marxa de la col·legiació mèdica.

El Pensamiento sanitario y laboral de dos medicos anarquistas del siglo XIX

Amb motiu del I Congrès Català de Medicina del treball, els autors recullen textos dispersos d'autors diversos del segle XIX en què podem observar una mateixa finalitat: la d'estudiar i resoldre problemes mèdico-laborals i de sanitat col·lectiva.

Legislación sanitaria marítima en Catalunya: 1717-1752

Aquesta publicació la formen les transcripcions d'unes disposicions legals establertes entre 1717 i 1752 pels guanyadors de la guerra de Successió (1702-1714). Es tracta doncs de legislació sanitària dictada específicament per al litoral marítim català. També trobem un estudi previ de l'autor sobre la situació política i social de la Catalunya i especialment de Barcelona després de la derrota de mans de les tropes de Felip V.

Diccionari biogràfic de metges catalans

Diccionari que recull una petita biografia i esment a les obres dels metges catalans de què es té constància desde l'Edat Mitja fins els temps contemporanis.

Nomina academicorum: 1770-1995

La publicació d'aquesta nòmina coincideix amb el 225è aniversari de la creació de la "Academia Médico Práctica de Barcelona", després anomenada Reial Acadèmia de Medicina de Catalunya. El llibre no pretén ser una història de l'Acadèmia si no que es limita a llistar els gairebé 350 membres numeraris de l'acadèmia. Ara bé, per fer-ho menys feixuc, s'han afegit breus referències sobre l'evolució, la composició i els locals on s'ha desenvolupat la seva activitat.

Balance del siglo XIX: la medicina

Amb motiu del Quart Congrés d'Història de la Medicina Catalana, es publica aquest recull d'articles del Doctor Robert, aparescuts a La Vanguardia a partir del 1901 i que aporten un testimoni directe d'un moment àlgid de la medicina catalana. Els recopil·ladors, en Josep M. Calbet i en Jacint Corbella, pretenen també destacar la implicació política d'aquest personatge tan rellevant.