Jaz Pérez

The multisymplectic Hamiltonian formalism is a generalization of the Hamiltonian formalism that manifestly preserves covariance in the description of fields and that has been proposed as a possible framework for developing a Lorentz-covariant, canonical quantization scheme. However, the possibility of defining multiple Poisson brackets within this formalism has significantly limited its practical use in field theory. In this paper, we establish a connection between the Lagrangian and multisymplectic descriptions of classical fields interacting with point particles in the field’s momentum representation by deriving the image of the de Donder–Weyl function for a general tensor representation of the Lorentz group. The calculation is carried out explicitly for the complex scalar field, the electromagnetic field, and the classical Dirac field. On this basis, we propose a Lorentz-covariant Poisson bracket with respect to the canonical variables of the fields, thereby opening the possibility of studying the complete system within a consistent relativistic and canonical framework.

Simple Summary: The present study evaluates the effects of two dietary supplements (guanidinoacetic acid [GAA] and zilpaterol hydrochloride [ZLH]) on the productive performance of fattening lambs over a 60-day period. The inclusion of these additives did not result in significant differences in the parameters studied. However, serum glucose and creatinine levels in the GAA group were higher than those in the control group. These findings suggest that further research is needed to determine the optimal dosage and duration of GAA supplementation to enhance lamb growth and meat production. Abstract: This study evaluated the effects of dietary supplementation with guanidinoacetic acid (GAA) and zilpaterol hydrochloride (ZLH) on productive performance, carcass traits, and blood chemistry in non-castrated male lambs over 60 days. Twenty-four Pelibuey × Dorper crossbred lambs (16.3 ± 2.7 kg) were adapted to housing and diet for 14 days before being randomly assigned to one of three treatments: (1) Control: total mixed ration (TMR) without additives; (2) GAA: TMR with 0.2% GAA; and (3) ZLH: TMR with 6 mg/kg dry matter (DM) of ZLH for the last 30 days. No significant differences were observed in productive performance or carcass traits among treatments. However, lambs fed GAA showed higher serum glucose and creatinine levels than the control group (p < 0.05), suggesting a potential effect on energy metabolism. ZLH supplementation had no measurable impact on the parameters evaluated. These findings indicate that while GAA may influence certain metabolic indicators, further research with extended feeding periods or varying dosages is needed to clarify its effects on growth and carcass characteristics in lambs.

The objective of this research is to conduct a comparative analysis of the two models of growth and development that were applied in Peru over the past six decades (1961-2021). The objective is to conduct a comparative analysis of the Import Substitution Model (ISM) and the Liberal Model (LM), to determine which of these models has demonstrated superior performance in terms of economic growth and social welfare for the country. In this instance, the documentary and systematic review of the material obtained from both physical and virtual libraries was employed as a method. Consequently, a variety of economic indicators have been examined, including the primary indicator of economic growth, gross domestic product (GDP), to account for the effects of inflation and ensure the accuracy of the data. Furthermore, the principal social indicators have been examined and contrasted to gauge the nation's social well-being. The findings of the study demonstrate that the ML has demonstrably outstripped the MSI in terms of economic growth and the enhancement of social welfare for Peruvian society over the past three decades. However, it would be erroneous to assume that this model has entirely resolved the country's economic and social challenges.

The pandemic outbreak in March 2020 and its associated sanitary regulations and restrictions triggered an abrupt and significant change for society in general and for families’ organization in particular. In Chile, the Santiago Metropolitan District was under a strict lockdown that involved the closure of the entire educational system. From a systemic-family stress perspective, the impact of these changes might have consequences not only for each individual family member, but for the parental dynamic and, consequently, for children’s well-being. This paper presents the results of a follow-up study showing changes in self-reported parental depression and the perceived home organization of mothers and fathers assessed at three different moments: before the pandemic, at the initial outbreak, and after 1 month of strict lockdown. Relevant moderators were explored using linear mixed models to understand the within-subject changes in mothers’ and fathers’ self-reports across the different assessment times. Financial strain, personality traits of self-criticism and dependency, previous parent–child quality interaction, recent major stressful events, and number of children are highlighted as relevant factors that moderate changes in home chaos and parental mental health perception. Significant risks and protective factors are described for fathers and mothers. The use of pre-pandemic measures as baseline levels enabled the identification of personal and family characteristics that were related to better outcomes. The results help increase our understanding of the sanitary regulations’ impacts on the family system and identify vulnerability indicators that should be considered.

The construct of the self is important in the domain of memory research. Recent work has shown that person memory is influenced by similarity of social targets to the self. The current experiments investigate self-similarity as defined by traits and political ideology to better understand how memory for social targets is organised. Across three experiments, participants formed positive or negative impressions based on each target’s picture, a trait-implying behavior (Experiments 1 & 2), and/or political ideology (conservative/liberal label in Experiment 2; political-ideological belief statements in Experiment 3) followed by a memory test. Results showed a self-similarity effect dependent on valence in Experiment 1, but not in Experiments 2 or 3 when participants processed ideological information associated with targets. These results suggest that self-similarity has an effect on memory for social targets, but that ideological information disrupts self-focused processing of others, suggesting that ideological information also has a powerful influence on what people remember about others (i.e. social targets).