This multi-methods study examined aspects of social and health service utilization among a sample of young marginalized crack users in two Brazilian cities (Rio de Janeiro and Salvador). Specifically, the study aimed to: 1) describe the utilization of key social and health services and identify factors associated with service use based on quantitative data; and 2) examine experiences, factors and dynamics of service access and use on the basis of qualitative data.
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The study [for details see Cruz et al. [55]] relied on quantitative and qualitative data from a cross-sectional multi-site study of regular street-involved crack users recruited from impoverished neighborhoods in Rio de Janeiro (e.g., Jacarezinho and Manguinhos) and Salvador (e.g., Pelourinho, Calabar, Ribeira, Fazenda Coutos and Valéria) with known large crack user populations. Participant recruitment was facilitated by community-based contact persons (e.g., community workers) with direct access to the target population. The community contacts disseminated information about the study to potential participants, who were then assessed for study eligibility on the basis of a few short screening questions.
However, respondents demonstrated little knowledge about the availability of or access procedures to drug abuse treatment facilities, and mostly were under the impression that there is a severe lack of such services. Conversely, most participants perceived there to be several shelters available in their cities that were prepared and open to receiving crack-addicted individuals. However, they considered those shelters rather unsuited to help or support the treatment of their addiction problems, also because they were considered dirty, disorganized, without leisure activities (for distraction) or longer-term treatment resources that would enable them to abstain from crack use.
Several participants from Salvador reported ongoing active crack use within such services. Respondents in Salvador also reported expressions of prejudice by drug addiction service professionals, saying that many professionals were not skilled or qualified to treat their addiction problems.
Some respondents in Rio furthermore stated that the existence of strict rules and schedules within their treatment programs would be necessary and helpful to increase the prospects of positive treatment outcomes. Some respondents voiced a desire to be able to smoke marijuana in the context of crack addiction treatment, as the use of marijuana would reduce their craving for crack and help them with their sleep and appetite.
Mainly drawing on our qualitative data, our results suggest that in regards to the services available, the vast majority of participants do not see these services well-suited for their needs, and they do not see themselves well-served in these facilities. While some of these barriers appear to relate to general problems, like lack of service capacity or resources, others refer to mundanely practical or bureaucratic issues (e.g., proof of residence) that are proven to affect marginalized populations more tangibly than others. Notably, participants also emphasized that they perceive many service providers not to be adequately prepared, qualified or experienced to deal with addiction-related health problems [68], or simply exert active stigma or prejudice against crack users preventing them from better utilizing much needed services. These obstacles and barriers to services targeting especially marginalized drug users specifically are well documented in other jurisdictions, and recognized as major contributors to highly compromised health status and care in these high-risk populations [42, 67, 69, 70]. Furthermore, our exploratory quantitative analyses of factors univariately associated with service utilization suggested that sex, and possibly housing status specifically appear to further influence the likelihood of service utilization in both sites.
In other interviews, crack users told us that drug abuse treatment facilities should provide referral to shelters. How should such shelters be designed and operated in order to work for you? Have you ever been in a shelter? What was your experience like?
The rate of O2-dependent cluster conversion of 5 μM [4Fe-4S] (A) D154A and (B) I151A FNR was measured by absorbance at 420 nm. Traces shown were recorded at O2 concentrations of 0, 20, 62, 103 and 124 μM for D154A and 0, 21, 63, 126 and 148 μM for I151A FNR. Data are shown in grey; fits to the experimental data are black. (C) Plots of the first observed (first-order) rate constants obtained from the data in (A) for D154A (grey circles) and (B) I151A (black triangles) and additional experiments (at O2 concentrations of 41, 82, 146, and 166 μM for D154A and 42, 84, 105 and 169 μM for I151A FNR) as a function of the O2 concentration. Least squares linear fits of the data are drawn in for D154A (grey line) and I151A (black line). The gradients of these lines correspond to the apparent second-order rate constants.
In this work, these three bioinspired architectures were constructed by 3-D printing Ti-6Al-4V scaffolds, which were then pressureless infiltrated with Mg to form Mg-Ti composites. This process utilizes the large difference in the melting points between the two constituents without severe chemical reaction, and the good wettability of the Mg melt with the Ti-6Al-4V alloy44,45. Our intent was to evaluate and compare the damage tolerance of these composites, specifically strength, toughness, and impact resistance (using the geometries shown in Supplementary Fig. 2), reveal their structure-property relationships, and clarify the toughening mechanisms associated with their specific bioinspired architectures. On this basis, we attempt to provide guidance for the architectural selection and design of bioinspired metallic materials. Further, we believe that our composites may also have the potential for structural and biomedical applications.
Figure 2 shows the fine microstructures, phase constitutions, and element distributions in Mg and Ti-6Al-4V constituents and at their interfaces, where the crossed-lamellar architecture is taken as an example (these characteristics were identical among the three architectures). The Ti-6Al-4V reinforcement was found to exhibit a fine basket-weave texture composed of α-Ti and β-Ti phases (Fig. 2a, b). Such a structure has been shown to be effective for arresting crack propagation in the alloy, thereby favoring improved fracture toughness46. Indeed, the Ti-6Al-4V phase exhibits similar microstructures and mechanical properties (as determined by nanoindentation testing) before and after melt infiltration, i.e., in the 3-D printed scaffolds and infiltrated composites (Supplementary Fig. 4). This indicates that the material properties of Ti-6Al-4V phase were essentially unaffected by the infiltration process.
In comparison, the crossed-lamellar architecture exhibited the broadest (non-localized) distribution of plastic deformation and damage extending over the entire gauge section (Fig. 3e). Abundant slip bands were formed within the Mg matrix, but were localized between adjacent Ti-6Al-4V platelets (inset). Moreover, the cracking paths were tortuous, both within the constituent layer (in-plane) and across different layers (out-of-plane), and were complicated by a number of branches at their deflecting points (inset). All these features suggest a more effective role of the crossed-lamellar architecture in delaying the final fracture of the composite, conforming well to its best-displayed combination of strength and ductility. By contrast, the plastic deformation was largely localized within the Mg matrix in the Mg alloy composites reinforced by discrete Ti-6Al-4V particles; cracking readily tended to occur and develop along the interfaces between the two phases29,30,31,32,33,34,49. As such, the enhanced mechanical properties of the bioinspired composites are closely associated with the delocalization of damage and the arrest of crack extension by the 3-D interpenetration of constituents and their specific architectures.
SEM images and CT volume renderings of the quasi-static fracture toughness samples for the composites with bioinspired (a) brick-and-mortar, (b) Bouligand, and (c) crossed-lamellar architectures. The CT images were processed by filtering out the signals of constituents and highlighting the cracking regions. The white arrows in (b) indicate the microcracks ahead of the crack tip. The inset in (c) magnifies the zig-zag cracking path and the resulted frictional sliding between crack faces as indicated by the arrows.
Figure 7 shows a direct comparison of mechanical properties among the three types of bioinspired composites with different architectures. The data for Mg alloy composite reinforced with discrete Ti-6Al-4V particles are also presented for comparison49. The yield strength (σYS), ultimate tensile strength (σUTS), and work of fracture (UF) are normalized by density (ρ) to compensate for the effects of their differences in phase constitution. The bioinspired architectures clearly endow the composites with higher strengths and work of fracture (as compared to the composites without bioinspired architectures). In addition, they play an effective role in delocalizing damage and resisting crack propagation under both quasi-static and dynamic loading conditions, bestowing improved ductility along with notable fracture and impact toughness properties.
The good mechanical properties of the bioinspired composites stem primarily from the following two aspects: First, the bicontinuous nature and interpenetration of the Mg and Ti-6Al-4V constituents in 3-D space allow for an effective stress transfer within and between each phase, thereby conferring a high strengthening efficiency of the reinforcement61,62,63. The deformation and cracking of the relatively weak Mg phase can also be restricted by the mutual partition of constituents; as a result the fracture of the entire composite can be retarded. Second, the specific bioinspired spatial arrangements of constituents create a series of extrinsic toughening mechanisms in the composites, specifically crack deflection/twist and uncracked-ligament bridging. These mechanisms act principally behind the crack tip and function to shield the crack tip from the applied stress64. Microcracks are also prone to emerge ahead of the crack tip as the crack inevitably encounters the Ti-6Al-4V reinforcement. This can direct the growing crack to deflect and twist and produce uncracked ligaments behind the crack tip, and by this means promote the above extrinsic toughening mechanisms. In addition, the interconnection between constituent layers, realized through the fusion joints formed during 3-D printing, is critical for avoiding the delamination of the composites, thereby ensuring the above strengthening and toughening effects of the architectures. In contrast, cracking is mainly localized within the Mg matrix and at the interfaces between constituents in the composites without bioinspired architectures29,30,31,32,33,34,49. Contributions to the fracture toughness are thus mainly developed from intrinsic toughening mechanisms which are related to the plasticity of the constituents64. 2ff7e9595c
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