WFU Physics Faculty and Students
George P. Williams, Jr. Lecture Hall, (Olin 101)
Wednesday, Sept. 18, 2019, at 3:00 PM


There will be a reception in the Olin Lounge at approximately 4 PM following the colloquium. All interested persons are cordially invited to attend.


PROGRAM

This colloquium will highlight physics research at Wake Forest University. During the colloquium, Physics Department faculty members and/or their students will present the essence of their research programs in the Physics Department. This forum for sharing ideas will hopefully inspire collaborations between students and faculty and between research groups.

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Professor Adam Wax
Department of Biomedical Engineering
Duke University
Durham, NC
George P. Williams, Jr. Lecture Hall, (Olin 101)
Wednesday, Sept. 25, 2019, at 3:00 PM

There will be a reception in the Olin Lounge at approximately 4 PM following the colloquium. All interested persons are cordially invited to attend.

ABSTRACT

The mechanisms by which cells respond to mechanical stimuli are essential for cell function yet not well understood. Many rheological tools have been developed to characterize cellular viscoelastic properties but these typically have limited throughput or require complex schemes. We have developed quantitative phase imaging methods which can image structural changes in cells due to mechanical stimuli at the nanoscale. These methods are label free and can image cells in culture or flowing through microfluidic
chips, providing high throughput measurements. We will present our single-shot phase imaging method that measures refractive index variance and relates it to disorder strength, which correlates to measured cellular mechanical properties such as shear modulus. Studies will be presented which relate mechanical properties to early carcinogenic events, investigate the role of specific cellular structural proteins in mechanotransduction and track water regulation due to mechanical stress.

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Professor Erin Henslee
Department of Engineering
Wake Forest University
Winston-Salem, NC
George P. Williams, Jr. Lecture Hall, (Olin 101)
Wednesday, Sept. 11, 2019, at 3:00 PM


There will be a reception in the Olin Lounge at approximately 4 PM following the colloquium. All interested persons are cordially invited to attend.


ABSTRACT

Dielectrophoresis (DEP), which is the induced motion of particles in non-uniform AC electric fields, is a label-free assay capable of characterizing cells based on their electrophysiological response. By varying the frequency of the electric field, it is possible to produce a profile of cell polarisability; the resultant electrophysiological spectra allow the determination of electrophysiological parameters including effective membrane conductance (Geff, -indicative of ionic transport across the membrane and on its surface), capacitance (Ceff, -indicative of membrane morphology and/or composition) and cytoplasmic conductivity (σcyt, indicative of free ionic concentration within the cytoplasm). In my work, I have applied DEP characterization as a rapid analysis tool in cancer diagnostics, circadian biomarkers, as well as characterizing stages of programed cell death (apoptosis) and drug efficacy. For this talk I will introduce 3DEP, the platform I was part of creating for this analysis, as well as some of the applications and future directions of the work.

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The Society for Physics Students (SPS) is hosting a cookout outside of Polo Hall on Monday Sept. 2, 2019 starting at 5:30 PM.   All Physics students (undergraduate majors, minors, and potentials, graduate students, etc.), faculty, and staff are welcome to join. Please sign up here.

Professor Jing Li
Department of Chemistry and Chemical Biology
Rutgers University
Piscataway, NJ USA
George P. Williams, Jr. Lecture Hall, (Olin 101)
Wednesday,Sept. 4, 2019, at 3:00 PM


There will be a reception in the Olin Lounge at approximately 4 PM following the colloquium. All interested persons are cordially invited to attend.


ABSTRACT

Metal-organic frameworks (MOFs) are a unique class of highly porous crystalline solids composed of periodically ordered and covalently bonded metal building units and organic ligands. In the past two decades MOFs have become one of the most intensively and extensively explored material families due to their enormous potential for a wide range of applications. MOFs are particularly promising as a new type of adsorbents for gas storage, capture and separation. They have demonstrated numerous advantages over conventional/traditional sorbent materials, not only due to their exceptionally high surface area, but also because of their nearly unlimited structural tunability and remarkable surface functionalizability.

Adsorptive separation of industrially relevant hydrocarbons is of paramount importance as it may substantially reduce the energy consumption required for the current distillation-based technology. However, finding an ideal adsorbent has been challenging as it requires precise control of the porosity (e.g. pore size, pore aperture, pore shape) and sorbent-sorbate interaction in order to meet the stringent performance requirement.

Guided by topological design strategy, we have recently succeeded in designing several MOFs with optimum pore structure.1-3 Built on zirconium and calcium metals and tetratopic carboxylate linkers they exhibit excellent stability towards heat, moisture and hush chemical environment. They show highly efficient separation of selected hydrocarbon mixtures, including alkane isomers and propane/propylene, with a performance surpassing benchmark adsorbents.

References:

  1. Wang, H.; Dong, X.L.; Lin, J.Z.; Teat, S.J.; Jensen, S.; Cure, J.; Alexandrov, E.V.; Xia, Q.B.; Wang, Q.N.; Olson, D.H.; Proserpio, D.M.; Chabal, Y.J.; Thonhauser, T.; Sun, J.L.; Han, Y.; Li, J. “Topologically Guided Tuning of Zr-MOF Pore Structures for Highly Selective Separation of C6 Alkane Isomers”, Nat. Commun., 2018, 9:1745.
  2. Wang, H.; Dong, X.L.; Velasco, E.; Olson, D.H.; Han, Y.; Li, J. “One-of-A-Kind: The First Example of Adsorptive Separation of Three Alkane Isomers by A Microporous Metal-Organic Framework via Temperature- and Adsorbate-Dependent Molecular Sieving”, Ene & Env Sci, 2018, 11, 1226-1231.
  3. Wang, H., Dong, X.L.; Colombo, V.; Wang, Q.N.; Liu, Y.Y.; Liu, W.; Wang, X.L.; Huang, X.Y.; Proserpio, D.M.; Sironi, S.; Han, Y.; Li, J. “Tailor-Made Microporous Metal-Organic Frameworks for the Full Separation of Propane from Propylene through Selective Size Exclusion”, Adv. Mater., 2018, 30, 201805088.

Link to Professor Jing Li’s web page

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George P. Williams, Jr. Lecture Hall, (Olin 101)
Wednesday, August 28, 2019, at 3 PM


There will be a reception in the Olin Lounge at approximately 4 PM following the colloquium. All interested persons are cordially invited to attend.


PROGRAM

The purpose of this first seminar is to help new, returning, and prospective students (including both undergraduate and graduate students), faculty, and staff to become acquainted with each other and with the Physics Department. We will meet in the George P. Williams, Jr. Lecture Hall (Olin 101) at 3:00 PM for presentations by some undergraduate students highlighting their summer research experiences, followed by general welcoming statements and departmental announcements.

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WFU Physics Honor Society (ΣΠΣ) and Department Awards Ceremony
George P. Williams, Jr. Lecture Hall, (Olin 101)
Wednesday, May 1, 2019, at 4:00 PM


There will be a reception with refreshments at 3:30 PM in the foyer. All interested persons are cordially invited to attend.

PROGRAM

  • Physics Honor Society (ΣΠΣ) Ceremony
  • Recognition of New Physics Department Majors
  • Physics Awards Ceremony

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WFU senior physics students will present highlights of their honors theses
George P. Williams, Jr. Lecture Hall, (Olin 101)
Wednesday, April 24, 2019, at 4:00 PM


There will be a reception with refreshments at 3:30 PM in the lounge. All interested persons are cordially invited to attend.

PROGRAM

  • Jacquelyn Sharpe— Mentor: Prof. Guthold — “Mechanical Properties of Electrospun 50:50 Fibrinogen:PCL Nanofibers”
  • Sean Yan— Mentor: Prof. Carroll — “All Inorganic Lead Halide Perovskite Core Shell Structure Nano-Inclusion Based Thin Film Light-Emitting Device Optimization
  • Cole Teander— Mentor: Prof. Thonhauser — “Using DFT to Predict the Elastic Moduli of Fourth Generation Metal-Organic Framework Materials”

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Paul W. Ayers, PhD
Department of Chemistry and Chemical Biology
McMaster University, Canada
George P. Williams, Jr. Lecture Hall, (Olin 101)
Wednesday, April 17, 2019, at 4:00 PM


There will be a reception with refreshments at 3:30 PM in the lounge. All interested persons are cordially invited to attend.


ABSTRACT

What happens when two substances are mixed together? Does a chemical reaction occur? If so, which chemical bonds are broken? What new chemical bonds are formed? Can we increase the efficiency of the reaction by changing the conditions under which it occurs? Questions like these lie at the core of chemistry. Addressing them requires understanding, at a fundamental level, how the electrons that bind atoms into molecules rearrange during the course of a chemical reaction and, more subtly, how different molecular environments influence these rearrangements. Therefore, in order to understand the nature of the chemical bond, and to master the chemical reactions by which chemical bonds are fractured and formed, we must uncover the inner lives of electrons.
The physical laws regulating how electrons behave in a molecular environment are encapsulated by the electronic Schrödinger equation. Unfortunately, highly-accurate solutions to the Schrödinger equation are rarely available for molecules containing more than four electrons, while most molecules of interest to chemists contain hundreds, or even thousands, of electrons. This impels the development of approximate models for electronic behavior. Such models are only effective in certain special cases. For example, it is relatively easy to describe cases where the electrons in a molecule move nearly independently, so that the motion of one electron does not affect the other electrons very much. It is also relatively easy to describe cases where the electrons in a molecule are rigidly correlated, so that moving one electron causes the other electrons to move in a nearly deterministic way. The electrons in most chemical substances lie between these two extremes, and developing practical computational methods for these in-between cases is the primary challenge of modern quantum chemistry. In this talk, I will reveal how quantum chemists develop new models for the behavior of electrons in molecules and materials. Some of the new methods are practical even for large molecules containing hundreds of electrons.

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Peiyun Li
Public Presentation in ZSR Library Auditorium
Monday, April 15, 2019 at 11 AM


There will be a reception with refreshments following the defense in Olin Lounge. All interested persons are cordially invited to attend the public talk and the reception.


ABSTRACT

Recent discoveries of rare-earth and alkaline-earth halides with scintillation activators and co-dopants showing excellent properties for spectroscopic gamma radiation detection attract a surge in research activity on their scintillation mechanisms. There is still much to learn about excited states in these materials. Understanding behaviors of the free carries and excitons in the first picoseconds are crucial for determining the speed and nonlinearity of response. Questions remain on whether and when the free electrons are trapped on holes, dopants or defects. The nature of interaction and recombination between the photon-excited species are also important. In this thesis, the crucial early evolution of excited populations is studied with picosecond spectroscopy of optical absorption induced by interband excitation.

We identified the self-trapped exciton (STE) absorption bands in LaBr3:Ce and CeBr3 samples along with a comparative study on the effects of Ce concentration on the STE absorption decay rate. The dominant scintillation mechanism of both LaBr3:Ce and CeBr3 is attributed to dipole-dipole energy transfer from the STE to Ce3+ dopant ions on the basis of the transient absorption bands. We identified the charge-transfer excitation of excited Ce3+* ions for the first time. The population rise time of the Ce3+* excited states in CeBr3 (~540 fs) is observed to be faster than in LaBr3:Ce, and reasons are described. We conclude that our picosecond absorption spectroscopy provides a unique method to assist in the improvement of timing resolution by isolating the rise time of population in the emitting state from the rise time of detected scintillation light, aiming for ultrafast time-of-flight detection.

We also studied the effects of interband excitation on undoped BaBrCl and on BaBrCl doped with Eu and/or Au, as measured by picosecond transient absorption spectroscopy. Aside from the identification of STE absorption bands in BaBrCl samples, we concluded that subsequent dipole-dipole energy transfer from STE to Eu is the dominant energy transfer mechanism. Au co-dopant in BaBrCl:Eu has been found to improve the scintillation light yield, and these transient absorption studies support that the mechanism involves suppression of the concentration of pre-existing halide vacancies.