Fragmentation phase transition in atomic clusters I --- Microcanonical thermodynamics

Here we first develop the thermodynamics of microcanonical phase transitions of first and second order in systems which are thermodynamically stable in the sense of van Hove. We show how both kinds of phase transitions can unambiguously be identified in relatively small isolated systems of $\sim 100$ atoms by the shape of the microcanonical caloric equation of state $$ I.e. within microcanonical thermodynamics one does not need to go to the thermodynamic limit in order to identify phase transitions. In contrast to ordinary (canonical) thermodynamics of the bulk microcanonical thermodynamics (MT) gives an insight into the coexistence region. The essential three parameters which identify the transition to be of first order, the transition temperature $T_{tr}$, the latent heat $q_{lat}$, and the interphase surface entropy $\Delta s_{surf}$ can very well be determined in relatively small systems like clusters by MT. The phase transition towards fragmentation is introduced. The general features of MT as applied to the fragmentation of atomic clusters are discussed. The similarities and differences to the boiling of macrosystems are pointed out.Comment: Same as before, abstract shortened my e-mail address: [email protected]

Experimental and Theoretical Search for a Phase Transition in Nuclear Fragmentation

Phase transitions of small isolated systems are signaled by the shape of the caloric equation of state e^*(T), the relationship between the excitation energy per nucleon e^* and temperature. In this work we compare the experimentally deduced e^*(T) to the theoretical predictions. The experimentally accessible temperature was extracted from evaporation spectra from incomplete fusion reactions leading to residue nuclei. The experimental e^*(T) dependence exhibits the characteristic S-shape at e^* = 2-3 MeV/A. Such behavior is expected for a finite system at a phase transition. The observed dependence agrees with predictions of the MMMC-model, which simulates the total accessible phase-space of fragmentation

Fragmentation Phase Transition in Atomic Clusters II - Coulomb Explosion of Metal Clusters -

We discuss the role and the treatment of polarization effects in many-body systems of charged conducting clusters and apply this to the statistical fragmentation of Na-clusters. We see a first order microcanonical phase transition in the fragmentation of $Na^{Z+}_{70}$ for Z=0 to 8. We can distinguish two fragmentation phases, namely evaporation of large particles from a large residue and a complete decay into small fragments only. Charging the cluster shifts the transition to lower excitation energies and forces the transition to disappear for charges higher than Z=8. At very high charges the fragmentation phase transition no longer occurs because the cluster Coulomb-explodes into small fragments even at excitation energy $\epsilon^* = 0$.Comment: 19 text pages +18 *.eps figures, my e-mail adress: [email protected] submitted to Z. Phys.

Impact of Gender on Separation-Reunification Experiences of Latino Adolescent Immigrants

Many Latino immigrants who enter the US in late childhood or adolescence are reunifying with parents after lengthy separations, and yet there is limited research on this process from their point of view. This article discusses the impact of gender relations on family re-engagement and immigrant adaptation of young men and young women. Young people were interviewed as part of a grounded theory study exploring the process of family separation and reunification for Latino immigrant adolescents who have been separated from their parents for at least four years during immigration. Focus groups, individual interviews and participant observation were used to gather data from 20 Mexican and Central American immigrant adolescents, 12 young men and 8 young women. Participants reported a range of personal and family beliefs about gender roles and their impact on separation and reunification, Young men reported greater exposure to violence, generally had less access to health care, and reported more emotional isolation from families and peers than young women. Fathers and adult male role models were missing from most of their lives, and this absence was particularly difficult for young men. Young women reported greater skills and persistence in emotional re-engagement with their families in the United States.Beaucoup d'immigrés latinos entrés aux Etats-Unis à la fin de l'enfance ou au début de l'adolescence retrouvent leurs parents après une longue période de séparation, et pourtant il n'existe que très peu d'études sur ce sujet relatant leur point de vue. Cet article traite de l'impact des rapports de genre sur le regroupement familial et l'adaptation des jeunes hommes et femmes immigrés. Des jeunes ont été interrogés dans le cadre d'une étude basée sur la théorie ancrée qui analysait le processus de séparation et de regroupement familial chez les adolescents immigrés latinos qui avaient été séparés de leurs parents pendant au moins quatre ans durant la période d'immigration. Des groupes cibles, des entretiens individuels et l'observation des participants ont permis de recueillir des données auprès de 20 adolescents immigrés originaires du Mexique et d'Amérique Centrale, dont 12 jeunes hommes et 8 jeunes femmes. Les participants ont décrit un ensemble de croyances personnelles et familiales sur les rôles sexuels, et leur impact sur la séparation et le regroupement familial. Les jeunes hommes ont ainsi déclaré être plus exposés à la violence, avoir généralement un accès aux soins plus limité, et souffrir d'une plus grande isolation émotionnelle vis-à-vis de leurs familles et de leurs pairs que les jeunes femmes. Les pères et les modèles adultes masculins étaient pour la plupart absents de leur vie, et cette absence était particulièrement difficile à vivre pour les jeunes hommes. Les jeunes femmes ont quant à elles montré plus de capacités et de persévérance dans le réengagement émotionnel avec leurs familles aux Etats-Unis.Muchos inmigrantes latinos que entran en Estados Unidos al final de su infancia o en su adolescencia  se reunifican con sus padres después de largos periodos de separación. Sin embargo, existen muy pocos estudios sobre este proceso desde su punto de vista. Este artículo analiza el impacto de las relaciones de género en la reunificación familiar y la adaptación como inmigrantes de hombres y mujeres jóvenes. Se entrevistó a chicos y chicas en el marco de un estudio de teoría fundamentada que explora el proceso de la separación familiar y su posterior reunificación en el caso de inmigrantes latinos adolescentes que han sido separados de sus padres durante al menos cuatro años en el transcurso de la inmigración. Se utilizaron reuniones de grupo, entrevistas individuales y observaciones para recabar datos de 20 inmigrantes adolescentes mexicanos y centroamericanos, 12 chicos y 8 chicas. Los participantes reflejaban diversas creencias personales y familiares sobre los roles de género y su impacto en la separación y reunificación. Los chicos reflejaron una mayor exposición a la violencia, un acceso más limitado en general a la asistencia sanitaria y un mayor aislamiento emocional de sus familias y compañeros que las chicas. En sus familias no había referencias paternas o de adultos masculinos y esta ausencia resultaba especialmente difícil para los chicos. Las chicas, en cambio, mostraron mayores habilidades y persistencia en la reunificación emocional con sus familias en suelo estadounidense

Impact of Gender on Separation-Reunification Experiences of Latino Adolescent Immigrants

Many Latino immigrants who enter the US in late childhood or adolescence are reunifying with parents after lengthy separations, and yet there is limited research on this process from their point of view. This article discusses the impact of gender relations on family re-engagement and immigrant adaptation of young men and young women. Young people were interviewed as part of a grounded theory study exploring the process of family separation and reunification for Latino immigrant adolescents who have been separated from their parents for at least four years during immigration. Focus groups, individual interviews and participant observation were used to gather data from 20 Mexican and Central American immigrant adolescents, 12 young men and 8 young women. Participants reported a range of personal and family beliefs about gender roles and their impact on separation and reunification, Young men reported greater exposure to violence, generally had less access to health care, and reported more emotional isolation from families and peers than young women. Fathers and adult male role models were missing from most of their lives, and this absence was particularly difficult for young men. Young women reported greater skills and persistence in emotional re-engagement with their families in the United States.Beaucoup d'immigrés latinos entrés aux Etats-Unis à la fin de l'enfance ou au début de l'adolescence retrouvent leurs parents après une longue période de séparation, et pourtant il n'existe que très peu d'études sur ce sujet relatant leur point de vue. Cet article traite de l'impact des rapports de genre sur le regroupement familial et l'adaptation des jeunes hommes et femmes immigrés. Des jeunes ont été interrogés dans le cadre d'une étude basée sur la théorie ancrée qui analysait le processus de séparation et de regroupement familial chez les adolescents immigrés latinos qui avaient été séparés de leurs parents pendant au moins quatre ans durant la période d'immigration. Des groupes cibles, des entretiens individuels et l'observation des participants ont permis de recueillir des données auprès de 20 adolescents immigrés originaires du Mexique et d'Amérique Centrale, dont 12 jeunes hommes et 8 jeunes femmes. Les participants ont décrit un ensemble de croyances personnelles et familiales sur les rôles sexuels, et leur impact sur la séparation et le regroupement familial. Les jeunes hommes ont ainsi déclaré être plus exposés à la violence, avoir généralement un accès aux soins plus limité, et souffrir d'une plus grande isolation émotionnelle vis-à-vis de leurs familles et de leurs pairs que les jeunes femmes. Les pères et les modèles adultes masculins étaient pour la plupart absents de leur vie, et cette absence était particulièrement difficile à vivre pour les jeunes hommes. Les jeunes femmes ont quant à elles montré plus de capacités et de persévérance dans le réengagement émotionnel avec leurs familles aux Etats-Unis.Muchos inmigrantes latinos que entran en Estados Unidos al final de su infancia o en su adolescencia  se reunifican con sus padres después de largos periodos de separación. Sin embargo, existen muy pocos estudios sobre este proceso desde su punto de vista. Este artículo analiza el impacto de las relaciones de género en la reunificación familiar y la adaptación como inmigrantes de hombres y mujeres jóvenes. Se entrevistó a chicos y chicas en el marco de un estudio de teoría fundamentada que explora el proceso de la separación familiar y su posterior reunificación en el caso de inmigrantes latinos adolescentes que han sido separados de sus padres durante al menos cuatro años en el transcurso de la inmigración. Se utilizaron reuniones de grupo, entrevistas individuales y observaciones para recabar datos de 20 inmigrantes adolescentes mexicanos y centroamericanos, 12 chicos y 8 chicas. Los participantes reflejaban diversas creencias personales y familiares sobre los roles de género y su impacto en la separación y reunificación. Los chicos reflejaron una mayor exposición a la violencia, un acceso más limitado en general a la asistencia sanitaria y un mayor aislamiento emocional de sus familias y compañeros que las chicas. En sus familias no había referencias paternas o de adultos masculinos y esta ausencia resultaba especialmente difícil para los chicos. Las chicas, en cambio, mostraron mayores habilidades y persistencia en la reunificación emocional con sus familias en suelo estadounidense

Evolution and the Expression of Biases: Situational Value Changes the Endowment Effect in Chimpanzees

Cognitive and behavioral biases, which are widespread among humans, have recently been demonstrated in other primates, suggesting a common origin. Here we examine whether the expression of one shared bias, the endowment effect, varies as a function of context. We tested whether objects lacking inherent value elicited a stronger endowment effect (or preference for keeping the object) in a context in which the objects had immediate instrumental value for obtaining valuable resources (food). Chimpanzee subjects had opportunities to trade tools when food was not present, visible but unobtainable, and obtainable using the tools. We found that the endowment effect for these tools existed only when they were immediately useful, showing that the effect varies as a function of context-specific utility. Such context-specific variation suggests that the variation seen in some human biases may trace predictably to behaviors that evolved to maximize gains in specific circumstances

Genetic Influences on Receptive Joint Attention in Chimpanzees (Pan troglodytes)

Despite their genetic similarity to humans, our understanding of the role of genes on cognitive traits in chimpanzees remains virtually unexplored. Here, we examined the relationship between genetic variation in the arginine vasopressin V1a receptor gene (AVPR1A) and social cognition in chimpanzees. Studies have shown that chimpanzees are polymorphic for a deletion in a sequence in the 59 flanking region of the AVPR1A, DupB, which contains the variable RS3 repetitive element, which has been associated with variation in social behavior in humans. Results revealed that performance on the social cognition task was significantly heritable. Furthermore, males with one DupB1 allele performed significantly better and were more responsive to socio-communicative cues than males homozygous for the DupB- deletion. Performance on a non-social cognition task was not associated with the AVPR1A genotype. The collective findings show that AVPR1A polymorphisms are associated with individual differences in performance on a receptive joint attention task in chimpanzees

Distal communication by chimpanzees (Pan troglodytes): evidence for common ground?

van der Goot et al. (2014) proposed that distal, deictic communication indexed the appreciation of the psychological state of a common ground between a signaler and a receiver. In their study, great apes did not signal distally, which they construed as evidence for the human uniqueness of a sense of common ground. This study exposed 166 chimpanzees to food and an experimenter, at an angular displacement, to ask, “Do chimpanzees display distal communication?” Apes were categorized as (a) proximal or (b) distal signalers on each of four trials. The number of chimpanzees who communicated proximally did not statistically differ from the number who signaled distally. Therefore, contrary to the claim by van der Goot et al., apes do communicate distally