Substance Use Initiation among Mexican Children: An Examination of Individual and Ecological Factors

Mexico is experiencing increased rates of substance use among children and adolescents. This is concerning as early substance use is associated with an increased risk for developing mental and physical health problems during adulthood. These outcomes may be prevented through early identification and intervention before individuals encounter the negative consequences of substance use/abuse. The current dissertation sought to improve our knowledge regarding factors associated with substance use and intention for first time use among Mexican children. Three manuscripts examined child individual characteristics and aspects of their environment. The first manuscript examined demographic characteristics to determine whether particular groups of children were at increased risk for substance use and intensions for first time use. We found that being a boy, of indigenous background, non-religious, and over developmental age for grade were all associated with risk. The second manuscript focuses on examining parent characteristics and practices on substance use and intention for first time use. We found that parental illicit substance use was associated with the largest increases in risk and positive parenting was a protective factor. The third manuscript utilized machine learning, an algorithmic approach that predicts membership in one of two groups, to assist in the identification of high value factors that distinguish between substance users and non-users. Findings from this research identified factors associated with childhood substance use at individual and environmental levels. Being a boy and having a best friend or father that used illicit substances were the key indicators that could provide valuable information as screening questions. These findings provide valuable information needed to inform the development of early substance use prevention programs in Mexico. Results also suggest that machine learning may be an important tool in uncovering information that could bolster prevention efforts by improving our ability to identify children at risk for substance use. This research was supported by the Utah State University Psychology Department and School of Graduate Studies

Validity of the linear growth equation for interface evolution for copper electrodeposition in the presence of organic additives

The interface evolution of copper electrodeposits produced on copper from a thiorea-derivative-containing acid plating bath at a low current density and 298 K was studied by atomic force microscopy (AFM). The dynamic scaling theory was applied to AFM images leading to scaling exponents, which are consistent with the predictions of the complete linear equation for interface growth. In agreement with the theory, experimental data show, for the interface evolution, a crossover from a surface diffusion controlled regime to an Edwards-Wilkinson regime as the length scale increases.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Self-affine fractal electrodeposited gold surfaces: Characterization by scanning tunneling microscopy

The morphological evolution of columnar gold electrodeposits grown at 100 nm s −1 by electroreducing a gold oxide layer on a gold cathode has been studied at a nanometer level by scanning tunneling microscopy. The interface thickness (ξ) depends on the scan length (L) as ξ∝ L α with α=0.49±0.07 for L > ds, where ds is the average top columnar size, and α=0.90±0.07 for L s. These results prove that the growing surface can be described as a self-affine fractal for length scales greater than the columnar size. Conversely, the columnar surface approaches the behavior of an Euclidean surface.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Self-affine fractal vapour-deposited gold surfaces characterization by scanning tunnelling microscopy

The morphological evolution of the surfaces of gold deposits grown from the vapour on smooth glass under nonequilibrium conditions and incident angle near substrate normal is studied at the nanometer level by scanning tunnelling microscopy. For an average film thickness equal to or greater than 500 nm, the interface thickness (ξ) reaches a steady state. Under these conditions, ξ depends on the scan length (L) as ξ ∝ Lα with α = 0.35 ± 0.05 for L > ds, where ds is the columnar size, and α = 0.89 ± 0.05 for L s. These results indicate that the growing surface spontaneously reaches a steady state and it can be described as a self-affine fractal. The value of α for L > ds agrees with the prediction of ballistic deposition models without restructuring, whereas that for L s exceeds the prediction of ballistic models including restructuring.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA)Facultad de Ciencias Exacta

Self-affine fractal electrodeposited gold surfaces: Characterization by scanning tunneling microscopy

The morphological evolution of columnar gold electrodeposits grown at 100 nm s −1 by electroreducing a gold oxide layer on a gold cathode has been studied at a nanometer level by scanning tunneling microscopy. The interface thickness (ξ) depends on the scan length (L) as ξ∝ L α with α=0.49±0.07 for L > ds, where ds is the average top columnar size, and α=0.90±0.07 for L s. These results prove that the growing surface can be described as a self-affine fractal for length scales greater than the columnar size. Conversely, the columnar surface approaches the behavior of an Euclidean surface.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Validity of the linear growth equation for interface evolution for copper electrodeposition in the presence of organic additives

The interface evolution of copper electrodeposits produced on copper from a thiorea-derivative-containing acid plating bath at a low current density and 298 K was studied by atomic force microscopy (AFM). The dynamic scaling theory was applied to AFM images leading to scaling exponents, which are consistent with the predictions of the complete linear equation for interface growth. In agreement with the theory, experimental data show, for the interface evolution, a crossover from a surface diffusion controlled regime to an Edwards-Wilkinson regime as the length scale increases.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Early stages of platinum electrodeposition on highly oriented pyrolytic graphite: scanning tunneling microscopy imaging and reaction pathway

The early stages of Pt electrodeposition (0.675-0.620 V vs RHE) on highly oriented pyrolytic graphite (HOPG) from chloroplatinic acid at 25 °C have been studied by ex-situ STM and SEM imaging complemented with electrochemical data. Nucleation and 3D growth of Pt initiate at HOPG surface defects. Large Pt agglomerates containing flat crystallites with well-defined geometries are found around HOPG steps. Pt crystallites formed by 1-2 nm size clusters become more compact as the electrodeposition potential is shifted negatively or the Pt electrodeposited charge is increased. High-resolution STM imaging reveals large uncovered HOPG areas with the nearest-neighbor C-C distance d = 0.24 ± 0.02 nm and fiat hexagonal Pt crystallites. Electrochemical data combined with STM imaging can be interpreted in terms of a diffusion-controlled Pt(IV) to Pt(II) reaction at HOPG and a surface reaction leading to Pt(0) at HOPG defects.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA)Facultad de Ciencias Exacta

Early stages of platinum electrodeposition on highly oriented pyrolytic graphite: scanning tunneling microscopy imaging and reaction pathway

The early stages of Pt electrodeposition (0.675-0.620 V vs RHE) on highly oriented pyrolytic graphite (HOPG) from chloroplatinic acid at 25 °C have been studied by ex-situ STM and SEM imaging complemented with electrochemical data. Nucleation and 3D growth of Pt initiate at HOPG surface defects. Large Pt agglomerates containing flat crystallites with well-defined geometries are found around HOPG steps. Pt crystallites formed by 1-2 nm size clusters become more compact as the electrodeposition potential is shifted negatively or the Pt electrodeposited charge is increased. High-resolution STM imaging reveals large uncovered HOPG areas with the nearest-neighbor C-C distance d = 0.24 ± 0.02 nm and fiat hexagonal Pt crystallites. Electrochemical data combined with STM imaging can be interpreted in terms of a diffusion-controlled Pt(IV) to Pt(II) reaction at HOPG and a surface reaction leading to Pt(0) at HOPG defects.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA)Facultad de Ciencias Exacta

Dynamic scaling exponents of copper electrodeposits from scanning force microscopy imaging : Influence of a thiourea additive on the kinetics of roughening and brightening

Changes in the topography of Cu electrodeposits grown on polycrystalline Cu substrates at low constant current density from still aqueous concentrated CuSO4 + H2SO4 solutions, at 298 K, were studied by scanning force microscopy (SFM) at different scale lengths (L) from the nanometer level upward. The dynamic scaling theory applied to SFM images leads to exponents α = 0.87 ± 0.06 and β = 0.63 ± 0.08, which are consistent with an interface growing under an unstable regime. For similar conditions, the addition of 1,3-diethyl-2-thiourea reduces the average crystal size (〈ds〉) of electrodeposits leading to scaling exponents α = 0.86 ± 0.06 and β = 0.24 ± 0.05 for L s⟩ and a logarithmic dependence for the spatial and temporal evolution of the interface for L > 3 μm and t → 0. In an additive-free plating bath, the unstable growth regime appears to be originated by enhanced electrodeposition at protrusions due to curvature effects and further sustained by the electric and concentration fields built up around the growing deposit. The presence of the additive hinders the development of instabilities driving the evolution of the growing interface to that predicted by the Edwards-Wilkinson growth model on the asymptotic limit.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Dynamic scaling exponents of copper electrodeposits from scanning force microscopy imaging : Influence of a thiourea additive on the kinetics of roughening and brightening

Changes in the topography of Cu electrodeposits grown on polycrystalline Cu substrates at low constant current density from still aqueous concentrated CuSO4 + H2SO4 solutions, at 298 K, were studied by scanning force microscopy (SFM) at different scale lengths (L) from the nanometer level upward. The dynamic scaling theory applied to SFM images leads to exponents α = 0.87 ± 0.06 and β = 0.63 ± 0.08, which are consistent with an interface growing under an unstable regime. For similar conditions, the addition of 1,3-diethyl-2-thiourea reduces the average crystal size (〈ds〉) of electrodeposits leading to scaling exponents α = 0.86 ± 0.06 and β = 0.24 ± 0.05 for L s⟩ and a logarithmic dependence for the spatial and temporal evolution of the interface for L > 3 μm and t → 0. In an additive-free plating bath, the unstable growth regime appears to be originated by enhanced electrodeposition at protrusions due to curvature effects and further sustained by the electric and concentration fields built up around the growing deposit. The presence of the additive hinders the development of instabilities driving the evolution of the growing interface to that predicted by the Edwards-Wilkinson growth model on the asymptotic limit.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta