Search

The interaction between passive and active/driven particles has introduced a new way to control colloidal suspension properties from particle aggregation to crystallization. Here, we focus on the hydrodynamic interaction between a single rotational driven particle and a suspension of passive particles near the floor. Using experiments and Stokesian dynamics simulations that account for near-field lubrication, we demonstrate that the flow induced by the driven particle can induce long-ranged rearrangement in a passive suspension. We observe an accumulation of passive particles in front of the driven particle and a depletion of passive particles behind the driven particle. This restructuring generates a pattern that can span a range more than $10$ times of the driven particle's radius. We further show that size scale of the pattern is only a function of the particle's height above the floor., Comment: S.-Y.C. and H.L-R. contributed equally

Colloidal crystals formed by size-asymmetric binary particles co-assemble into a wide variety of colloidal compounds with lattices akin to ionic crystals. Recently, a transition from a compound phase with a sublattice of small particles to a metal-like phase in which the small particles are delocalized has been predicted computationally and observed experimentally. In this colloidal metallic phase, the small particles roam the crystal maintaining the integrity of the lattice of large particles, as electrons do in metals. A similar transition also occurs in superionic crystals, termed sublattice melting. Here, we use energetic principles and a generalized molecular dynamics model of a binary system of functionalized nanoparticles to analyze the transition to sublattice delocalization in different co-assembled crystal phases as a function of T, number of grafted chains on the small particles, and number ratio between the small and large particles $n_s$:$n_l$. We find that $n_s$:$n_l$ is the primary determinant of crystal type due to energetic interactions and interstitial site filling, while the number of grafted chains per small particle determines the stability of these crystals. We observe first-order sublattice delocalization transitions as T increases, in which the host lattice transforms from low- to high-symmetry crystal structures, including A20 to BCT to BCC, Ad to BCT to BCC, and BCC to BCC/FCC to FCC transitions and lattices. Analogous sublattice transitions driven primarily by lattice vibrations have been seen in some atomic materials exhibiting an insulator-metal transition also referred to as metallization. We also find minima in the lattice vibrations and diffusion coefficient of small particles as a function of $n_s$:$n_l$, indicating enhanced stability of certain crystal structures for $n_s$:$n_l$ values that form compounds., Comment: AE and HL-R contributed equally to this work

Sublattice melting is the loss of order of one lattice component in binary or ternary ionic crystals upon increase in temperature. A related transition has been predicted in colloidal crystals. To understand the nature of this transition, we study delocalization in self-assembled, size asymmetric binary colloidal crystals using a generalized molecular dynamics model. Focusing on BCC lattices, we observe a smooth change from localized-to-delocalized interstitial particles for a variety of interaction strengths. Thermodynamic arguments, mainly the absence of a discontinuity in the heat capacity, suggest that the passage from localization-to-delocalization is continuous and not a phase transition. This change is enhanced by lattice vibrations, and the temperature of the onset of delocalization can be tuned by the strength of the interaction between the colloid species. Therefore, the localized and delocalized regimes of the sublattice are dominated by enthalpic and entropic driving forces, respectively. This work sets the stage for future studies of sublattice melting in colloidal systems with different stoichiometries and lattice types, and it provides insights into superionic materials, which have potential for application in energy storage technologies., Comment: Hector Lopez-Rios and Ali Ehlen contributed equally

High-performance materials rely on small reorganization energies to facilitate both charge separation and charge transport. Here, we performed DFT calculations to predict small reorganization energies of rectangular silicene nanoclusters with hydrogen-passivated edges denoted by H-SiNC. We observe that across all geometries, H-SiNCs feature large electron affinities and highly stabilized anionic states, indicating their potential as n-type materials. Our findings suggest that fine-tuning the size of H-SiNCs along the zigzag and armchair directions may permit the design of novel n-type electronic materials and spinctronics devices that incorporate both high electron affinities and very low internal reorganization energies., Comment: 25 pages, 6 figures

This paper illustrates the application of the collaborative problem solving process for academic and behavioral remediation for students experiencing low reading achievement and some behavioral problems. Unlike the traditional psychoeducational process in which the relationship between the school psychologist and the teacher is that of consultant and consultee, this approach establishes a reciprocal, interdependent working partnership. On the basis of this cooperative association, a mutually agreed upon curriculum-based intervention plan was devised and implemented for a second-grade student who concomitantly demonstrated behavioral problems. Results of the intervention show that the student's reading ability and his desire to pay attention during class time increased, while his off-task and disruptive behaviors decreased. (MKA)

This paper describes the process and procedures that three Rowan graduate students of school psychology, in collaboration with two faculty members, utilize to plan and deliver school psychology services. Overall, the cases show how school psychologists can influence the academic achievement of not only an individual child but also a whole class, as well as a whole system. Two cases illustrate the benefits of collaborative consultation while another describes the need to look at systematic variables (e.g., curriculum) and their impact on individual learners. The idea that psychologists need to act as consultants to schools as systems has gained much momentum within the past 10 years. The NASP position statement on advocacy for appropriate educational services for all children and the subsequent publications, "Alternative Educational Delivery Systems: Enhancing Instructional Options for All Students" and "Best Practices in School Psychology III," provide the philosophical and theoretical bases for an expanded role for school psychologists. New roles require that school psychologists provide expertise as appropriate to the various school-based services and programs. Changes in roles and behavior call for new ways of communicating information, planning, and decision making. As a consultant, the school psychologist is a resource within the natural learning environment, using curriculum-based educational and instructional methodologies to collaboratively identify problems and devise solutions. These cases indicate this approach is beneficial because it provides help at the pre-referral stage, thus possibly preventing identifying children as disabled; it provides services for more students; and it makes full use of the professional capabilities of the educators involved, producing a multiplicative rather than an additive effect. (Author/MKA)