Gun Enforcement and Gun Violence Prevention Practices among Local Law Enforcement Agencies: A Research and Policy Brief

Controlling gun crime continues to be a difficult challenge for policymakers and practitioners in the United States. In 2009, there were roughly 11,000 murders with firearms in the United State and another 326,000 non-fatal violent crimes with guns . The prevalence of guns is thought to contribute to particularly high levels of homicide in the United States, where some estimates imply that the total costs of gun violence -- including medical, criminal justice, and other costs -- could be well over $100 billion per year.Yet finding common ground for legislative solutions to this problem is quite difficult, making it especially critical to effectively enforce existing laws and utilize other prevention approaches. Indeed, debates on controlling firearms violence often revolve around whether the nation needs tougher gun laws or better enforcement of laws that already exist. However, these debates are not well informed by systematic information on what law enforcement agencies are doing to reduce gun violence, the success of those efforts, and the factors that facilitate or hinder those efforts. In order to inform debate on these issues and to highlight successful enforcement and prevention strategies to reduce gun violence, the Police Executive Research Forum (PERF) undertook a national study of gun violence prevention efforts by local police in urban jurisdictions. The study's objectives were to: 1) to describe the range, scope, and prevalence of police efforts to reduce gun violence; 2) to assess which practices are most effective, both generally and in combination with different gun laws; and 3) to determine how these efforts can be improved

Aging dynamics of ferromagnetic and reentrant spin glass phases in stage-2 Cu0.80_{0.80}C0.20_{0.20}Cl2_{2} graphite intercalation compound

Aging dynamics of a reentrant ferromagnet stage-2 Cu$_{0.8}$Co$_{0.2}$Cl$_{2}$ graphite intercalation compound has been studied using DC magnetic susceptibility. This compound undergoes successive transitions at the transition temperatures $T_{c}$ ($\approx 8.7$ K) and $T_{RSG}$ ($\approx 3.3$ K). The relaxation rate $S_{ZFC}(t)$ exhibits a characteristic peak at $t_{cr}$ below $T_{c}$. The peak time $t_{cr}$ as a function of temperature $T$ shows a local maximum around 5.5 K, reflecting a frustrated nature of the ferromagnetic phase. It drastically increases with decreasing temperature below $T_{RSG}$. The spin configuration imprinted at the stop and wait process at a stop temperature $T_{s}$ ($<T_{c}$) during the field-cooled aging protocol, becomes frozen on further cooling. On reheating, the memory of the aging at $T_{s}$ is retrieved as an anomaly of the thermoremnant magnetization at $T_{s}$. These results indicate the occurrence of the aging phenomena in the ferromagnetic phase ($T_{RSG}<T<T_{c}$) as well as in the reentrant spin glass phase ($T<T_{RSG}$).Comment: 9 pages, 9 figures; submitted to Physical Review

Incomplete approach to homoclinicity in a model with bent-slow manifold geometry

The dynamics of a model, originally proposed for a type of instability in plastic flow, has been investigated in detail. The bifurcation portrait of the system in two physically relevant parameters exhibits a rich variety of dynamical behaviour, including period bubbling and period adding or Farey sequences. The complex bifurcation sequences, characterized by Mixed Mode Oscillations, exhibit partial features of Shilnikov and Gavrilov-Shilnikov scenario. Utilizing the fact that the model has disparate time scales of dynamics, we explain the origin of the relaxation oscillations using the geometrical structure of the bent-slow manifold. Based on a local analysis, we calculate the maximum number of small amplitude oscillations, $s$, in the periodic orbit of $L^s$ type, for a given value of the control parameter. This further leads to a scaling relation for the small amplitude oscillations. The incomplete approach to homoclinicity is shown to be a result of the finite rate of `softening' of the eigen values of the saddle focus fixed point. The latter is a consequence of the physically relevant constraint of the system which translates into the occurrence of back-to-back Hopf bifurcation.Comment: 14 Figures(Postscript); To Appear in Physica D : Nonlinear Phenomen

Landing and catalytic characterization of individual nanoparticles on electrode surfaces

We demonstrate a novel and versatile pipet-based approach to study the landing of individual nanoparticles (NPs) on various electrode materials without any need for encapsulation or fabrication of complex substrate electrode structures, providing great flexibility with respect to electrode materials. Because of the small electrode area defined by the pipet dimensions, the background current is low, allowing for the detection of minute current signals with good time resolution. This approach was used to characterize the potential-dependent activity of Au NPs and to measure the catalytic activity of a single NP on a TEM grid, combining electrochemical and physical characterization at the single NP level for the first time. Such measurements open up the possibility of studying the relation between the size, structure and activity of catalyst particles unambiguously

Aging dynamics in reentrant ferromagnet: Cu0.2_{0.2}Co0.8_{0.8}Cl2_{2}-FeCl3_{3} graphite bi-intercalation compound

Aging dynamics of a reentrant ferromagnet Cu$_{0.2}$Co$_{0.8}$Cl$_{2}$-FeCl$_{3}$ graphite bi-intercalation compound has been studied using AC and DC magnetic susceptibility. This compound undergoes successive transitions at the transition temperatures $T_{c}$ ($= 9.7$ K) and $T_{RSG}$ ($= 3.5$ K). The relaxation rate $S(t)$ exhibits a characteristic peak at $t_{cr}$ close to a wait time $t_{w}$ below $T_{c}$, indicating that the aging phenomena occur in both the reentrant spin glass (RSG) phase below $T_{RSG}$ and the ferromagnetic (FM) phase between $T_{RSG}$ and $T_{c}$. The relaxation rate $S(t)$ ($=\text{d}\chi_{ZFC}(t)/\text{d}\ln t$) in the FM phase exhibits two peaks around $t_{w}$ and a time much shorter than $t_{w}$ under the positive $T$-shift aging, indicating a partial rejuvenation of domains. The aging state in the FM phase is fragile against a weak magnetic-field perturbation. The time ($t$) dependence of $\chi_{ZFC}(t)$ around $t \approx t_{cr}$ is well approximated by a stretched exponential relaxation: $\chi_{ZFC}(t) \approx \exp[-(t/\tau)^{1-n}]$. The exponent $n$ depends on $t_{w}$, $T$, and $H$. The relaxation time $\tau$ ($\approx t_{cr}$) exhibits a local maximum around 5 K, reflecting a chaotic nature of the FM phase. It drastically increases with decreasing temperature below $T_{RSG}$.Comment: 16 pages,16 figures, submitted to Physical Review

Resilience, well-being and informal and formal support in multi-problem families during the Covid-19 pandemic

BACKGROUND: The Covid-19 pandemic may have had negative effects on youth and parental mental health, especially in high-risk populations such as multi-problem families (i.e., families that experience problems in multiple domains, such as mental health and social network problems). Using one to four assessments during all phases of the Covid-19 pandemic up until January 2022, we examined the associations between pandemic-related stress and mental health (resilience and well-being) of youth and parents from multi-problem families. We also investigated whether experienced informal (i.e., youth informal mentoring) and formal support (i.e., therapist support) served as protective factors in this association. METHODS: A total of 92 youth aged 10–19 years (46.7% girls; mean age 16.00 years) and 78 parents (79.5% female; mean age 47.17 years) filled in one to four questionnaires between March 2020 and January 2022. Multi-level analyses were conducted to account for the nested structure of the data. RESULTS: For youth, pandemic-related stress was associated with lower well-being, but not with resilience. Perceived support from both mentors and therapists was positively associated with youth mental health. Furthermore, high perceived therapist support protected youth from the negative effect of pandemic-related stress on resilience. For parents, pandemic-related stress was not related to mental health, irrespective of therapist support. Yet, therapist support was directly and positively associated with parental mental health. CONCLUSIONS: Youth from multi-problem families who experience pandemic-related stress are at risk of (elevated) mental health problems during the pandemic, specifically if they have no or weak therapist support. The mental health of parents, however, was minimally affected by pandemic-related stress, indicating strength and flexibility. Youth and parents who experienced support during the pandemic reported higher levels of resilience and well-being, demonstrating the importance of support for individuals’ mental health during stressful times such as a pandemic. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s13034-022-00542-2