Eric C. Landahl
DePaul University
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Featured researches published by Eric C. Landahl.
Journal of Synchrotron Radiation | 2009
T. Ejdrup; Henrik T. Lemke; K. Haldrup; T. N. Nielsen; D. A. Arms; Donald A. Walko; Antonino Miceli; Eric C. Landahl; Eric M. Dufresne; M.M. Nielsen
The recent developments in X-ray detectors have opened new possibilities in the area of time-resolved pump/probe X-ray experiments; this article presents the novel use of a PILATUS detector to achieve X-ray pulse duration limited time-resolution at the Advanced Photon Source (APS), USA. The capability of the gated PILATUS detector to selectively detect the signal from a given X-ray pulse in 24 bunch mode at the APS storage ring is demonstrated. A test experiment performed on polycrystalline organic thin films of alpha-perylene illustrates the possibility of reaching an X-ray pulse duration limited time-resolution of 60 ps using the gated PILATUS detector. This is the first demonstration of X-ray pulse duration limited data recorded using an area detector without the use of a mechanical chopper array at the beamline.
EMBO Reports | 2013
Julian L. Klosowiak; Pamela J. Focia; Srinivas Chakravarthy; Eric C. Landahl; Douglas M. Freymann; Sarah E. Rice
Miro is a highly conserved calcium‐binding GTPase at the regulatory nexus of mitochondrial transport and autophagy. Here we present crystal structures comprising the tandem EF hand and carboxy terminal GTPase (cGTPase) domains of Drosophila Miro. The structures reveal two previously unidentified ‘hidden’ EF hands, each paired with a canonical EF hand. Each EF hand pair is bound to a helix that structurally mimics an EF hand ligand. A key nucleotide‐sensing element and a Pink1 phosphorylation site both lie within an extensive EF hand–cGTPase interface. Our results indicate structural mechanisms for calcium, nucleotide and phosphorylation‐dependent regulation of mitochondrial function by Miro.
Physical Chemistry Chemical Physics | 2009
Adam G. Larson; Eric C. Landahl; Sarah E. Rice
Two recent theoretical advances have described cargo transport by multiple identical motors and by multiple oppositely directed, but otherwise identical motors [M. J. Muller, S. Klumpp and R. Lipowsky, Proc. Natl. Acad. Sci. U. S. A., 2008, 105(12), 4609-4614; S. Klumpp and R. Lipowsky, Proc. Natl. Acad. Sci. U. S. A., 2005, 102(48), 17284-17289]. Here, we combine a similar theoretical approach with a simple experiment to describe the behaviour of a system comprised of slow and fast molecular motors having the same directionality. We observed the movement of microtubules by mixtures of slow and fast kinesin motors attached to a glass coverslip in a classic sliding filament assay. The motors are identical, except that the slow ones contain five point mutations that collectively reduce their velocity approximately 15-fold without compromising maximal ATPase activity. Our results indicate that a small fraction of fast motors are able to accelerate the dissociation of slow motors from microtubules. Because of this, a sharp, highly cooperative transition occurs from slow to fast microtubule movement as the relative number of fast motors in the assay is increased. Microtubules move at half-maximal velocity when only 15% of the motors in the assay are fast. Our model indicates that this behaviour depends primarily on the relative motor velocities and the asymmetry between their forward and backward dissociation forces. It weakly depends on the number of motors and their processivity. We predict that movement of cargoes bound to two types of motors having very different velocities will be dominated by one or the other motor. Therefore, cargoes can potentially undergo abrupt changes in movement in response to regulatory mechanisms acting on only a small fraction of motors.
SRI 2009, 10TH INTERNATIONAL CONFERENCE ON RADIATION INSTRUMENTATION | 2010
Eric M. Dufresne; Bernhard W. Adams; D. A. Arms; Matthieu Chollet; Eric C. Landahl; Yuelin Li; Donald A. Walko; Jin Wang
The Sector 7 undulator beamline (7‐ID) of the Advanced Photon Source (APS) is dedicated to time‐resolved x‐ray research and is capable of ultrafast measurements on the order of 100 ps. Beamline 7‐ID has a laser laboratory featuring a Ti:Sapphire system (average power of 2.5 W, pulse duration <50 fs, repetition rate 1–5 kHz) that can be synchronized to the bunch pattern of the storage ring. The laser is deliverable to x‐ray enclosures, which contain diffractometers, as well as motorized optical tables for table‐top experiments. Beamline 7‐ID has a single APS Undulator A and uses a diamond (111) double‐crystal monochromator, providing good energy resolution over a range of 6–24 keV. Available optics include Kirkpatrick‐Baez (KB) mirrors to microfocus the x‐ray beam. A variety of time‐resolved diffraction and spectroscopy research is available at 7‐ID, with experiments being done in the atomic, molecular, optical, chemistry, and solid state (bulk and surface) fields.
Optics Communications | 1998
Eric C. Landahl; David Baiocchi; John R. Thompson
Abstract An analytic model for first Stokes–Raman generation in optical fiber is used to evaluate the relative importance of quantum initiation noise and amplified classical pump noise in recent experiments on noise shaping. The model accounts for pump depletion and for fluctuations arising from the spontaneous generation of the first Stokes pulse, but not for scattering into higher-order Stokes pulses. The model reproduces the qualitative features of the measured first Stokes pulse energy statistics using realistic parameter values.
Scientific Reports | 2016
Sooheyong Lee; G. Jackson Williams; Maria I. Campana; Donald A. Walko; Eric C. Landahl
Using a strain-rosette, we demonstrate the existence of transverse strain using time-resolved x-ray diffraction from multiple Bragg reflections in laser-excited bulk gallium arsenide. We find that anisotropic strain is responsible for a considerable fraction of the total lattice motion at early times before thermal equilibrium is achieved. Our measurements are described by a new model where the Poisson ratio drives transverse motion, resulting in the creation of shear waves without the need for an indirect process such as mode conversion at an interface. Using the same excitation geometry with the narrow-gap semiconductor indium antimonide, we detected coherent transverse acoustic oscillations at frequencies of several GHz.
Journal of Synchrotron Radiation | 2016
Steve Ross; Michael J. Haji-Sheikh; Andrew S. Huntington; David Kline; Adam Lee; Yuelin Li; Jehyuk Rhee; Mary Tarpley; Donald A. Walko; Gregg Westberg; George M. Williams; Haifeng Zou; Eric C. Landahl
The Voxtel VX-798 is a prototype X-ray pixel array detector (PAD) featuring a silicon sensor photodiode array of 48 × 48 pixels, each 130 µm × 130 µm × 520 µm thick, coupled to a CMOS readout application specific integrated circuit (ASIC). The first synchrotron X-ray characterization of this detector is presented, and its ability to selectively count individual X-rays within two independent arrival time windows, a programmable energy range, and localized to a single pixel is demonstrated. During our first trial run at Argonne National Laboratorys Advance Photon Source, the detector achieved a 60 ns gating time and 700 eV full width at half-maximum energy resolution in agreement with design parameters. Each pixel of the PAD holds two independent digital counters, and the discriminator for X-ray energy features both an upper and lower threshold to window the energy of interest discarding unwanted background. This smart-pixel technology allows energy and time resolution to be set and optimized in software. It is found that the detector linearity follows an isolated dead-time model, implying that megahertz count rates should be possible in each pixel. Measurement of the line and point spread functions showed negligible spatial blurring. When combined with the timing structure of the synchrotron storage ring, it is demonstrated that the area detector can perform both picosecond time-resolved X-ray diffraction and fluorescence spectroscopy measurements.
SRI 2009, 10TH INTERNATIONAL CONFERENCE ON RADIATION INSTRUMENTATION | 2010
Donald A. Walko; D. A. Arms; Eric M. Dufresne; Eric C. Landahl
The high x‐ray flux available at synchrotron radiation sources can cause nonlinearities in photon‐counting detectors unless deadtime corrections are employed. We compute the uncertainties associated with several common deadtime‐correction formulas. At lower countrates, statistical noise dominates the error in the measured countrates; at higher countrates, the dominating factors are saturation of the response and uncertainty in the value of the deadtime parameter. In between, a range of countrates exists in which the signal‐to‐noise ratio can be optimized for photon‐counting experiments.
Scientific Reports | 2016
G. Jackson Williams; Sooheyong Lee; Donald A. Walko; Michael A. Watson; Wonhuyk Jo; Dong Ryeol Lee; Eric C. Landahl
Nonlinear optical phenomena in semiconductors present several fundamental problems in modern optics that are of great importance for the development of optoelectronic devices. In particular, the details of photo-induced lattice dynamics at early time-scales prior to carrier recombination remain poorly understood. We demonstrate the first integrated measurements of both optical and structural, material-dependent quantities while also inferring the bulk impulsive strain profile by using high spatial-resolution time-resolved x-ray scattering (TRXS) on bulk crystalline gallium arsenide. Our findings reveal distinctive laser-fluence dependent crystal lattice responses, which are not described by previous TRXS experiments or models. The initial linear expansion of the crystal upon laser excitation stagnates at a laser fluence corresponding to the saturation of the free carrier density before resuming expansion in a third regime at higher fluences where two-photon absorption becomes dominant. Our interpretations of the lattice dynamics as nonlinear optical effects are confirmed by numerical simulations and by additional measurements in an n-type semiconductor that allows higher-order nonlinear optical processes to be directly observed as modulations of x-ray diffraction lineshapes.
Review of Scientific Instruments | 2016
Wonhyuk Jo; Intae Eom; Eric C. Landahl; Sooheyong Lee; Chung-Jong Yu
We report on the development of a new experimental instrument for time-resolved x-ray scattering (TRXS) at the Pohang Light Source (PLS-II). It operates with a photon energy ranging from 5 to 18 keV. It is equipped with an amplified Ti:sappahire femtosecond laser, optical diagnostics, and laser beam delivery for pump-probe experiments. A high-speed single-element detector and high trigger-rate oscilloscope are used for rapid data acquisition. While this instrument is capable of measuring sub-nanosecond dynamics using standard laser pump/x-ray probe techniques, it also takes advantage of the dense 500 MHz standard fill pattern in the PLS-II storage ring to efficiently record nano-to-micro-second dynamics simultaneously. We demonstrate this capability by measuring both the (fast) impulsive strain and (slower) thermal recovery dynamics of a crystalline InSb sample following intense ultrafast laser excitation. Exploiting the full repetition rate of the storage ring results in a significant improvement in data collection rates compared to conventional bunch-tagging methods.