85 research outputs found
Research on Access and Success of Under-Represented Groups in the Geosciences
The geosciences as an allied group of fields touch virtually all aspects of the human enterprise: locating and providing water, energy and mineral resources; assuring a safe and resilient environment for civilization; and providing an understanding of how the Earth system functions today, in the past and into the future. Given how the geosciences touch the lives of all people, it should also be a field that is representative of all people, but this is not yet the case. Especially with the global importance of the geosciences growing and the geoscience workforce projected to encounter shortfalls of qualified practitioners in the coming decades, it is imperative that the geoscience education research community frame and investigate central questions that can help increase the diversity of the geosciences at all levels. We must find ways to attract all kinds of students, especially those from under-represented groups to our sciences and build programs, experiences and careers in which they thrive. The research challenges proposed in this chapter focus on two essential and interdependent perspectives (1) the point of view of the individual students, faculty and professionals as they manage their own internal balance of identities as they traverse curricula, programs and career pathways, and (2) a view that captures system-wide interactions around the individuals at all stages, including family, culture, department, university and society
Strategies for Targeted Delivery to the Peripheral Nerve
Delivery of compounds to the peripheral nervous system has the potential to be used as a treatment for a broad range of conditions and applications, including neuropathic pain, regional anesthesia, traumatic nerve injury, and inherited and inflammatory neuropathies. However, efficient delivery of therapeutic doses can be difficult to achieve due to peripheral neuroanatomy and the restrictiveness of the blood-nerve barrier. Depending on the underlying integrity of the blood-nerve barrier in the application at hand, several strategies can be employed to navigate the peripheral nerve architecture and facilitate targeted delivery to the peripheral nerve. This review describes different applications where targeted delivery to the peripheral nervous system is desired, the challenges that the blood-nerve barrier poses in each application, and bioengineering strategies that can facilitate delivery in each application
Edge of a Half-Filled Landau Level
We have investigated the electron occupation number of the edge of a quantum
Hall (QH) droplet at using exact diagonalization technique and
composite fermion trial wavefunction. We find that the electron occupation
numbers near the edge obey a scaling behavior. The scaling result indicates the
existence of a well-defined edge corresponding to the radius of a compact
droplet of uniform filling factor 1/2. We find that the occupation number
beyond this edge point is substantial, which is qualitatively different from
the case of odd-denominator QH states. We relate these features to the
different ways in which composite fermions occupy Landau levels for odd and
even denominator states.Comment: To appear in Phys. Rev.
Enhanced Viability of Endothelial Colony Forming Cells in Fibrin Microbeads for Sensor Vascularization
Enhanced vascularization at sensor interfaces can improve long-term function. Fibrin, a natural polymer, has shown promise as a biomaterial for sensor coating due to its ability to sustain endothelial cell growth and promote local vascularization. However, the culture of cells, particularly endothelial cells (EC), within 3D scaffolds for more than a few days is challenging due to rapid loss of EC viability. In this manuscript, a robust method for developing fibrin microbead scaffolds for long-term culture of encapsulated ECs is described. Fibrin microbeads are formed using sodium alginate as a structural template. The size, swelling and structural properties of the microbeads were varied with needle gauge and composition and concentration of the pre-gel solution. Endothelial colony-forming cells (ECFCs) were suspended in the fibrin beads and cultured within a perfusion bioreactor system. The perfusion bioreactor enhanced ECFCs viability and genome stability in fibrin beads relative to static culture. Perfusion bioreactors enable 3D culture of ECs within fibrin beads for potential application as a sensor coating
Imaging of poly(α-hydroxy-ester) scaffolds with X-ray phase-contrast microcomputed tomography
Porous scaffolds based on poly(α-hydroxy-esters) are under investigation in many tissue engineering applications. A biological response to these materials is driven, in part, by their three-dimensional (3D) structure. The ability to evaluate quantitatively the material structure in tissue-engineering applications is important for the continued development of these polymer-based approaches. X-ray imaging techniques based on phase contrast (PC) have shown a tremendous promise for a number of biomedical applications owing to their ability to provide a contrast based on alternative X-ray properties (refraction and scatter) in addition to X-ray absorption. In this research, poly(α-hydroxy-ester) scaffolds were synthesized and imaged by X-ray PC microcomputed tomography. The 3D images depicting the X-ray attenuation and phase-shifting properties were reconstructed from the measurement data. The scaffold structure could be imaged by X-ray PC in both cell culture conditions and within the tissue. The 3D images allowed for quantification of scaffold properties and automatic segmentation of scaffolds from the surrounding hard and soft tissues. These results provide evidence of the significant potential of techniques based on X-ray PC for imaging polymer scaffolds
Edge reconstructions in fractional quantum Hall systems
Two dimensional electron systems exhibiting the fractional quantum Hall
effects are characterized by a quantized Hall conductance and a dissipationless
bulk. The transport in these systems occurs only at the edges where gapless
excitations are present. We present a {\it microscopic} calculation of the edge
states in the fractional quantum Hall systems at various filling factors using
the extended Hamiltonian theory of the fractional quantum Hall effect. We find
that at the quantum Hall edge undergoes a reconstruction as the
background potential softens, whereas quantum Hall edges at higher filling
factors, such as , are robust against reconstruction. We present
the results for the dependence of the edge states on various system parameters
such as temperature, functional form and range of electron-electron
interactions, and the confining potential. Our results have implications for
the tunneling experiments into the edge of a fractional quantum Hall system.Comment: 11 pages, 9 figures; minor typos corrected; added 2 reference
Exchange anisotropy, disorder and frustration in diluted, predominantly ferromagnetic, Heisenberg spin systems
Motivated by the recent suggestion of anisotropic effective exchange
interactions between Mn spins in GaMnAs (arising as a result of
spin-orbit coupling), we study their effects in diluted Heisenberg spin
systems. We perform Monte Carlo simulations on several phenomenological model
spin Hamiltonians, and investigate the extent to which frustration induced by
anisotropic exchanges can reduce the low temperature magnetization in these
models and the interplay of this effect with disorder in the exchange. In a
model with low coordination number and purely ferromagnetic (FM) exchanges, we
find that the low temperature magnetization is gradually reduced as exchange
anisotropy is turned on. However, as the connectivity of the model is
increased, the effect of small-to-moderate anisotropy is suppressed, and the
magnetization regains its maximum saturation value at low temperatures unless
the distribution of exchanges is very wide. To obtain significant suppression
of the low temperature magnetization in a model with high connectivity, as is
found for long-range interactions, we find it necessary to have both
ferromagnetic and antiferromagnetic (AFM) exchanges (e.g. as in the RKKY
interaction). This implies that disorder in the sign of the exchange
interaction is much more effective in suppressing magnetization at low
temperatures than exchange anisotropy.Comment: 9 pages, 8 figure
Spin-flip scattering in the quantum Hall regime
We present a microscopic theory of spin-orbit coupling in the integer quantum
Hall regime. The spin-orbit scattering length is evaluated in the limit of
long-range random potential. The spin-flip rate is shown to be determined by
rare fluctuations of anomalously high electric field. A mechanism of strong
spin-orbit scattering associated with exchange-induced spontaneous
spin-polarization is suggested. Scaling of the spin-splitting of the
delocalization transition with the strength of spin-orbit and exchange
interactions is also discussed.Comment: References added, small additional comments, to appear in Phys. Rev.
B; 23 pages, RevTeX 3.
Correlated few-electron states in vertical double-quantum-dot systems
The electronic properties of semiconductor, vertical, double quantum dot
systems with few electrons are investigated by means of analytic,
configuration-interaction, and mean-field methods. The combined effect of a
high magnetic field, electrostatic confinement, and inter-dot coupling, induces
a new class of few-electron ground states absent in single quantum dots. In
particular, the role played by the isospin (or quantum dot index) in
determining the appearance of new ground states is analyzed and compared with
the role played by the standard spin.Comment: 20 pages, Latex, figures upon request. To appear in Phys. Rev. B
(January 1995
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