A LOW-E MAGIC ANGLE SPINNING PROBE FOR BIOLOGICAL SOLID STATE NMR AT 750 MHz

PubMed Central

McNeill, Seth A.; Gor’kov, Peter L.; Shetty, Kiran; Brey, William W.; Long, Joanna R.

2009-01-01

Crossed-coil NMR probes are a useful tool for reducing sample heating for biological solid state NMR. In a crossed-coil probe, the higher frequency 1H field, which is the primary source of sample heating in conventional probes, is produced by a separate low-inductance resonator. Because a smaller driving voltage is required, the electric field across the sample and the resultant heating is reduced. In this work we describe the development of a magic angle spinning (MAS) solid state NMR probe utilizing a dual resonator. This dual resonator approach, referred to as “Low-E,” was originally developed to reduce heating in samples of mechanically aligned membranes. The study of inherently dilute systems, such as proteins in lipid bilayers, via MAS techniques requires large sample volumes at high field to obtain spectra with adequate signal-to-noise ratio under physiologically relevant conditions. With the Low-E approach, we are able to obtain homogeneous and sufficiently strong radiofrequency fields for both 1H and 13C frequencies in a 4 mm probe with a 1H frequency of 750 MHz. The performance of the probe using windowless dipolar recoupling sequences is demonstrated on model compounds as well as membrane embedded peptides. PMID:19138870

Nitroxide amide-BODIPY probe behavior in fibroblasts analyzed by advanced fluorescence microscopy.

PubMed

Liras, M; Simoncelli, S; Rivas-Aravena, A; García, O; Scaiano, J C; Alarcon, E I; Aspée, A

2016-04-26

A novel synthesized nitroxide amide-BODIPY prefluorescent probe was used to study cellular redox balance that modulates nitroxide/hydroxylamine ratio in cultured human fibroblasts. FLIM quantitatively differentiated between nitroxide states of the cytoplasm-localized probe imaged by TIRF, monitoring nitroxide depletion by hydrogen peroxide; eluding incorrect interpretation if only fluorescence intensity is considered.

Picosecond excite-and-probe absorption measurement of the 4T2 state nonradiative lifetime in ruby

NASA Technical Reports Server (NTRS)

Gayen, S. K.; Wang, W. B.; Petricevic, V.; Dorsinville, R.; Alfano, R. R.

1985-01-01

In a picosecond excite-and-probe absorption measurement, a 527-nm picosecond pulse excites the 4T2 state of the Cr(3+) ion in ruby and a 3.4-micron picosecond probe pulse monitors the growth and decay of population in the 2E state as a function of pump-probe delay. From the growth of population in the metastable 2E state, an upper limit of 7 ps for the nonradiative lifetime of the 4T2 state is determined.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jin Jiasen; Yu Changshui; Song Heshan

We propose a scheme for identifying an unknown Bell diagonal state. In our scheme the measurements are performed on the probe qubits instead of the Bell diagonal state. The distinct advantage is that the quantum state of the evolved Bell diagonal state ensemble plus probe states will still collapse on the original Bell diagonal state ensemble after the measurement on probe states; i.e., our identification is quantum state nondestructive. How to realize our scheme in the framework of cavity electrodynamics is also shown.

An excited state intramolecular proton transfer dye based fluorescence turn-on probe for fast detection of thiols and its applications in bioimaging

NASA Astrophysics Data System (ADS)

Zhao, Yun; Xue, Yuanyuan; Li, Haoyang; Zhu, Ruitao; Ren, Yuehong; Shi, Qinghua; Wang, Song; Guo, Wei

2017-03-01

In this study, a new fluorescent probe 2-(2‧-hydroxy-5‧-N-maleimide phenyl)-benzothiazole (probe 1), was designed and synthesized by linking the excited state intramolecular proton transfer (ESIPT) fluorophore to the maleimide group for selective detection of thiols in aqueous solution. The fluorescence of probe 1 is strongly quenched by maleimide group through the photo-induced electron transfer (PET) mechanism, but after reaction with thiol, the fluorescence of ESIPT fluorophore is restored, affording a large Stokes shifts. Upon addition of cysteine (Cys), probe 1 exhibited a fast response time (complete within 30 s) and a high signal-to-noise ratio (up to 23-fold). It showed a high selectivity and excellent sensitivity to thiols over other relevant biological species, with a detection limit of 3.78 × 10- 8 M (S/N = 3). Moreover, the probe was successfully applied to the imaging of thiols in living cells.

Optical switch probes and optical lock-in detection (OLID) imaging microscopy: high-contrast fluorescence imaging within living systems.

PubMed

Yan, Yuling; Marriott, M Emma; Petchprayoon, Chutima; Marriott, Gerard

2011-02-01

Few to single molecule imaging of fluorescent probe molecules can provide information on the distribution, dynamics, interactions and activity of specific fluorescently tagged proteins during cellular processes. Unfortunately, these imaging studies are made challenging in living cells because of fluorescence signals from endogenous cofactors. Moreover, related background signals within multi-cell systems and intact tissue are even higher and reduce signal contrast even for ensemble populations of probe molecules. High-contrast optical imaging within high-background environments will therefore require new ideas on the design of fluorescence probes, and the way their fluorescence signals are generated and analysed to form an image. To this end, in the present review we describe recent studies on a new family of fluorescent probe called optical switches, with descriptions of the mechanisms that underlie their ability to undergo rapid and reversible transitions between two distinct states. Optical manipulation of the fluorescent and non-fluorescent states of an optical switch probe generates a modulated fluorescence signal that can be isolated from a larger unmodulated background by using OLID (optical lock-in detection) techniques. The present review concludes with a discussion on select applications of synthetic and genetically encoded optical switch probes and OLID microscopy for high-contrast imaging of specific proteins and membrane structures within living systems.

Dicke superradiance as nondestructive probe for the state of atoms in optical lattices

NASA Astrophysics Data System (ADS)

ten Brinke, Nicolai; Schützhold, Ralf

2016-04-01

We present a proposal for a probing scheme utilizing Dicke superradiance to obtain information about ultracold atoms in optical lattices. A probe photon is absorbed collectively by an ensemble of lattice atoms generating a Dicke state. The lattice dynamics (e.g., tunneling) affects the coherence properties of that Dicke state and thus alters the superradiant emission characteristics - which in turn provides insight into the lattice (dynamics). Comparing the Bose-Hubbard and the Fermi-Hubbard model, we find similar superradiance in the strongly interacting Mott insulator regime, but crucial differences in the weakly interacting (superfluid or metallic) phase. Furthermore, we study the possibility to detect whether a quantum phase transition between the two regimes can be considered adiabatic or a quantum quench.

An off-on fluorescence probe targeting mitochondria based on oxidation-reduction response for tumor cell and tissue imaging

NASA Astrophysics Data System (ADS)

Yao, Hanchun; Cao, Li; Zhao, Weiwei; Zhang, Suge; Zeng, Man; Du, Bin

2017-10-01

In this study, a tumor-targeting poly( d, l-lactic-co-glycolic acid) (PLGA) loaded "off-on" fluorescent probe nanoparticle (PFN) delivery system was developed to evaluate the region of tumor by off-on fluorescence. The biodegradability of the nanosize PFN delivery system readily released the probe under tumor acidic conditions. The probe with good biocompatibility was used to monitor the intracellular glutathione (GSH) of cancer cells and selectively localize to mitochondria for tumor imaging. The incorporated tumor-targeting probe was based on the molecular photoinduced electron transfer (PET) mechanism preventing fluorescence ("off" state) and could be easily released under tumor acidic conditions. However, the released tumor-targeting fluorescence probe molecule was selective towards GSH with high selectivity and an ultra-sensitivity for the mitochondria of cancer cells and tissues significantly increasing the probe molecule fluorescence signal ("on" state). The tumor-targeting fluorescence probe showed sensitivity to GSH avoiding interference from cysteine and homocysteine. The PFNs could enable fluorescence-guided cancer imaging during cancer therapy. This work may expand the biological applications of PFNs as a diagnostic reagent, which will be beneficial for fundamental research in tumor imaging. [Figure not available: see fulltext.

Ultrafast carrier dynamics in band edge and broad deep defect emission ZnSe nanowires

NASA Astrophysics Data System (ADS)

Othonos, Andreas; Lioudakis, Emmanouil; Philipose, U.; Ruda, Harry E.

2007-12-01

Ultrafast carrier dynamics of ZnSe nanowires grown under different growth conditions have been studied. Transient absorption measurements reveal the dependence of the competing effects of state filling and photoinduced absorption on the probed energy states. The relaxation of the photogenerated carriers occupying defect states in the stoichiometric and Se-rich samples are single exponentials with time constants of 3-4ps. State filling is the main contribution for probe energies below 1.85eV in the Zn-rich grown sample. This ultrafast carrier dynamics study provides an important insight into the role that intrinsic point defects play in the observed photoluminescence from ZnSe nanowires.

Reversible optical control of cyanine fluorescence in fixed and living cells: optical lock-in detection immunofluorescence imaging microscopy

PubMed Central

Yan, Yuling; Petchprayoon, Chutima; Mao, Shu; Marriott, Gerard

2013-01-01

Optical switch probes undergo rapid and reversible transitions between two distinct states, one of which may fluoresce. This class of probe is used in various super-resolution imaging techniques and in the high-contrast imaging technique of optical lock-in detection (OLID) microscopy. Here, we introduce optimized optical switches for studies in living cells under standard conditions of cell culture. In particular, a highly fluorescent cyanine probe (Cy or Cy3) is directly or indirectly linked to naphthoxazine (NISO), a highly efficient optical switch that undergoes robust, 405/532 nm-driven transitions between a colourless spiro (SP) state and a colourful merocyanine (MC) state. The intensity of Cy fluorescence in these Cy/Cy3-NISO probes is reversibly modulated between a low and high value in SP and MC states, respectively, as a result of Förster resonance energy transfer. Cy/Cy3-NISO probes are targeted to specific proteins in living cells where defined waveforms of Cy3 fluorescence are generated by optical switching of the SP and MC states. Finally, we introduce a new imaging technique (called OLID-immunofluorescence microscopy) that combines optical modulation of Cy3 fluorescence from Cy3/NISO co-labelled antibodies within fixed cells and OLID analysis to significantly improve image contrast in samples having high background or rare antigens. PMID:23267183

Charge and pairing dynamics in the attractive Hubbard model: Mode coupling and the validity of linear-response theory

NASA Astrophysics Data System (ADS)

Bünemann, Jörg; Seibold, Götz

2017-12-01

Pump-probe experiments have turned out as a powerful tool in order to study the dynamics of competing orders in a large variety of materials. The corresponding analysis of the data often relies on standard linear-response theory generalized to nonequilibrium situations. Here we examine the validity of such an approach for the charge and pairing response of systems with charge-density wave and (or) superconducting (SC) order. Our investigations are based on the attractive Hubbard model which we study within the time-dependent Hartree-Fock approximation. In particular, we calculate the quench and pump-probe dynamics for SC and charge order parameters in order to analyze the frequency spectra and the coupling of the probe field to the specific excitations. Our calculations reveal that the "linear-response assumption" is justified for small to moderate nonequilibrium situations (i.e., pump pulses) in the case of a purely charge-ordered ground state. However, the pump-probe dynamics on top of a superconducting ground state is determined by phase and amplitude modes which get coupled far from the equilibrium state indicating the failure of the linear-response assumption.

Time-resolved photoelectron spectroscopy of adenosine and adenosine monophosphate photodeactivation dynamics in water microjets

NASA Astrophysics Data System (ADS)

Williams, Holly L.; Erickson, Blake A.; Neumark, Daniel M.

2018-05-01

The excited state relaxation dynamics of adenosine and adenosine monophosphate were studied at multiple excitation energies using femtosecond time-resolved photoelectron spectroscopy in a liquid water microjet. At pump energies of 4.69-4.97 eV, the lowest ππ* excited state, S1, was accessed and its decay dynamics were probed via ionization at 6.20 eV. By reversing the role of the pump and probe lasers, a higher-lying ππ* state was excited at 6.20 eV and its time-evolving photoelectron spectrum was monitored at probe energies of 4.69-4.97 eV. The S1 ππ* excited state was found to decay with a lifetime ranging from ˜210 to 250 fs in adenosine and ˜220 to 250 fs in adenosine monophosphate. This lifetime drops with increasing pump photon energy. Signal from the higher-lying ππ* excited state decayed on a time scale of ˜320 fs and was measureable only in adenosine monophosphate.

The Effects of Probe Similarity on Retrieval and Comparison Processes in Associative Recognition.

PubMed

Zhang, Qiong; Walsh, Matthew M; Anderson, John R

2017-02-01

In this study, we investigated the information processing stages underlying associative recognition. We recorded EEG data while participants performed a task that involved deciding whether a probe word triple matched any previously studied triple. We varied the similarity between probes and studied triples. According to a model of associative recognition developed in the Adaptive Control of Thought-Rational cognitive architecture, probe similarity affects the duration of the retrieval stage: Retrieval is fastest when the probe is similar to a studied triple. This effect may be obscured, however, by the duration of the comparison stage, which is fastest when the probe is not similar to the retrieved triple. Owing to the opposing effects of probe similarity on retrieval and comparison, overall RTs provide little information about each stage's duration. As such, we evaluated the model using a novel approach that decomposes the EEG signal into a sequence of latent states and provides information about the durations of the underlying information processing stages. The approach uses a hidden semi-Markov model to identify brief sinusoidal peaks (called bumps) that mark the onsets of distinct cognitive stages. The analysis confirmed that probe type has opposite effects on retrieval and comparison stages.

Open quantum dots—probing the quantum to classical transition

NASA Astrophysics Data System (ADS)

Ferry, D. K.; Burke, A. M.; Akis, R.; Brunner, R.; Day, T. E.; Meisels, R.; Kuchar, F.; Bird, J. P.; Bennett, B. R.

2011-04-01

Quantum dots provide a natural system in which to study both quantum and classical features of transport. As a closed testbed, they provide a natural system with a very rich set of eigenstates. When coupled to the environment through a pair of quantum point contacts, each of which passes several modes, the original quantum environment evolves into a set of decoherent and coherent states, which classically would compose a mixed phase space. The manner of this breakup is governed strongly by Zurek's decoherence theory, and the remaining coherent states possess all the properties of his pointer states. These states are naturally studied via traditional magnetotransport at low temperatures. More recently, we have used scanning gate (conductance) microscopy to probe the nature of the coherent states, and have shown that families of states exist through the spectrum in a manner consistent with quantum Darwinism. In this review, we discuss the nature of the various states, how they are formed, and the signatures that appear in magnetotransport and general conductance studies.

Light, Molecules, Action: Using Ultrafast Uv-Visible and X-Ray Spectroscopy to Probe Excited State Dynamics in Photoactive Molecules

NASA Astrophysics Data System (ADS)

Sension, R. J.

2017-06-01

Light provides a versatile energy source capable of precise manipulation of material systems on size scales ranging from molecular to macroscopic. Photochemistry provides the means for transforming light energy from photon to process via movement of charge, a change in shape, a change in size, or the cleavage of a bond. Photochemistry produces action. In the work to be presented here ultrafast UV-Visible pump-probe, and pump-repump-probe methods have been used to probe the excited state dynamics of stilbene-based molecular motors, cyclohexadiene-based switches, and polyene-based photoacids. Both ultrafast UV-Visible and X-ray absorption spectroscopies have been applied to the study of cobalamin (vitamin B_{12}) based compounds. Optical measurements provide precise characterization of spectroscopic signatures of the intermediate species on the S_{1} surface, while time-resolved XANES spectra at the Co K-edge probe the structural changes that accompany these transformations.

Experimental Studies of Intent Information on Cockpit Traffic Displays

NASA Technical Reports Server (NTRS)

Barhydt, Richard; Hansman, R. John, Jr.

1997-01-01

Intent information provides knowledge of another aircraft's current and future trajectory states. Prototype traffic displays were designed for four different levels of intent: No Intent, Rate, Commanded State, and Flight Management System (FMS)-Path. The TCAS Display was used as a baseline and represents the No Intent Level. The Rate, Commanded State, and FMS-Path Displays show increasing levels of intent information using TCAS-like symbology in addition to incorporating a conflict probe and profile view display. An experiment was run on the MIT Part Task Flight Simulator in which eight airline pilots flew five traffic scenarios with each of the four displays. Results show that pilots had fewer separation violations and maneuvered earlier with the three intent displays. Separation violations were reduced when pilots maneuvered earlier. A second experiment was run to compare performance between displaying intent information directly and incorporating it into a conflict probe. A different set of eight airline pilots flew four traffic scenarios with the TCAS and Commanded State Displays with and without the conflict probe. Conflict probes with two minute and long range look-ahead times were tested. Displaying conflict bands or showing intent information directly both led to fewer separation violations and earlier avoidance maneuvers than the base TCAS Display. Performance was similar between the two minute and long range look-ahead conflict probes. Pilots preferred all intent displays over the TCAS Display.

Deciphering excited state evolution in halorhodopsin with stimulated emission pumping.

PubMed

Bismuth, Oshrat; Komm, Pavel; Friedman, Noga; Eliash, Tamar; Sheves, Mordechai; Ruhman, Sanford

2010-03-04

The primary photochemical dynamics of Hb. pharaonis Halorhodopsin (pHR) are investigated by femtosecond visible pump-near IR dump-hyperspectral probe spectroscopy. The efficiency of excited state depletion is deduced from transient changes in absorption, recorded with and without stimulated emission pumping (SEP), as a function of the dump delay. The concomitant reduction of photocycle population is assessed by probing the "K" intermediate difference spectrum. Results show that the cross section for stimulating emission is nearly constant throughout the fluorescent state lifetime. Probing "K" demonstrates that dumping produces a proportionate reduction in photocycle yields. We conclude that, despite its nonexponential internal conversion (IC) kinetics, the fluorescent state in pHR constitutes a single intermediate in the photocycle. This contrasts with conclusions drawn from the study of primary events in the related chloride pump from Hb. salinarum (sHR), believed to produce the "K" intermediate from a distinct short-lived subpopulation in the excited state. Our discoveries concerning internal conversion dynamics in pHR are discussed in light of recent expectations for similar excited state dynamics in both proteins.

Multiple quantum coherence spectroscopy.

PubMed

Mathew, Nathan A; Yurs, Lena A; Block, Stephen B; Pakoulev, Andrei V; Kornau, Kathryn M; Wright, John C

2009-08-20

Multiple quantum coherences provide a powerful approach for studies of complex systems because increasing the number of quantum states in a quantum mechanical superposition state increases the selectivity of a spectroscopic measurement. We show that frequency domain multiple quantum coherence multidimensional spectroscopy can create these superposition states using different frequency excitation pulses. The superposition state is created using two excitation frequencies to excite the symmetric and asymmetric stretch modes in a rhodium dicarbonyl chelate and the dynamic Stark effect to climb the vibrational ladders involving different overtone and combination band states. A monochromator resolves the free induction decay of different coherences comprising the superposition state. The three spectral dimensions provide the selectivity required to observe 19 different spectral features associated with fully coherent nonlinear processes involving up to 11 interactions with the excitation fields. The different features act as spectroscopic probes of the diagonal and off-diagonal parts of the molecular potential energy hypersurface. This approach can be considered as a coherent pump-probe spectroscopy where the pump is a series of excitation pulses that prepares a multiple quantum coherence and the probe is another series of pulses that creates the output coherence.

A Common Probe Design for Multiple Planetary Destinations

NASA Technical Reports Server (NTRS)

Hwang, H. H.; Allen, G. A., Jr.; Alunni, A. I.; Amato, M. J.; Atkinson, D. H.; Bienstock, B. J.; Cruz, J. R.; Dillman, R. A.; Cianciolo, A. D.; Elliott, J. O.;

Effects of Electronic-State-Dependent Solute Polarizability: Application to Solute-Pump/Solvent-Probe Spectra.

PubMed

Sun, Xiang; Ladanyi, Branka M; Stratt, Richard M

2015-07-23

Experimental studies of solvation dynamics in liquids invariably ask how changing a solute from its electronic ground state to an electronically excited state affects a solution's dynamics. With traditional time-dependent-fluorescence experiments, that means looking for the dynamical consequences of the concomitant change in solute-solvent potential energy. But if one follows the shift in the dynamics through its effects on the macroscopic polarizability, as recent solute-pump/solvent-probe spectra do, there is another effect of the electronic excitation that should be considered: the jump in the solute's own polarizability. We examine the spectroscopic consequences of this solute polarizability change in the classic example of the solvation dye coumarin 153 dissolved in acetonitrile. After demonstrating that standard quantum chemical methods can be used to construct accurate multisite models for the polarizabilities of ground- and excited-state solvation dyes, we show via simulation that this polarizability change acts as a contrast agent, significantly enhancing the observable differences in optical-Kerr spectra between ground- and excited-state solutions. A comparison of our results with experimental solute-pump/solvent-probe spectra supports our interpretation and modeling of this spectroscopy. We predict, in particular, that solute-pump/solvent-probe spectra should be sensitive to changes in both the solvent dynamics near the solute and the electronic-state-dependence of the solute's own rotational dynamics.

Investigation of electronically excited indole relaxation dynamics via photoionization and fragmentation pump-probe spectroscopy.

PubMed

Godfrey, T J; Yu, Hui; Ullrich, Susanne

2014-07-28

The studies herein investigate the involvement of the low-lying (1)La and (1)Lb states with (1)ππ(*) character and the (1)πσ(*) state in the deactivation process of indole following photoexcitation at 201 nm. Three gas-phase, pump-probe spectroscopic techniques are employed: (1) Time-resolved photoelectron spectroscopy (TR-PES), (2) hydrogen atom (H-atom) time-resolved kinetic energy release (TR-KER), and (3) time-resolved ion yield (TR-IY). Each technique provides complementary information specific to the photophysical processes in the indole molecule. In conjunction, a thorough examination of the electronically excited states in the relaxation process, with particular focus on the involvement of the (1)πσ(*) state, is afforded. Through an extensive analysis of the TR-PES data presented here, it is deduced that the initial excitation of the (1)Bb state decays to the (1)La state on a timescale beyond the resolution of the current experimental setup. Relaxation proceeds on the (1)La state with an ultrafast decay constant (<100 femtoseconds (fs)) to the lower-lying (1)Lb state, which is found to possess a relatively long lifetime of 23 ± 5 picoseconds (ps) before regressing to the ground state. These studies also manifest an additional component with a relaxation time of 405 ± 76 fs, which is correlated with activity along the (1)πσ(*) state. TR-KER and TR-IY experiments, both specifically probing (1)πσ(*) dynamics, exhibit similar decay constants, further validating these observations.

Pump-dump-probe and pump-repump-probe ultrafast spectroscopy resolves cross section of an early ground state intermediate and stimulated emission in the photoreactions of the Pr ground state of the cyanobacterial phytochrome Cph1.

PubMed

Fitzpatrick, Ann E; Lincoln, Craig N; van Wilderen, Luuk J G W; van Thor, Jasper J

2012-01-26

The primary photoreactions of the red absorbing ground state (Pr) of the cyanobacterial phytochrome Cph1 from Synechocystis PCC 6803 involve C15═C16 Z-E photoisomerization of its phycocyanobilin chromophore. The first observable product intermediate in pump-probe measurements of the photocycle, "Lumi-R", is formed with picosecond kinetics and involves excited state decay reactions that have 3 and 14 ps time constants. Here, we have studied the photochemical formation of the Lumi-R intermediate using multipulse picosecond visible spectroscopy. Pump-dump-probe (PDP) and pump-repump-probe (PRP) experiments were carried out by employing two femtosecond visible pulses with 1, 14, and 160 ps delays, together with a broadband dispersive visible probe. The time delays between the two excitation pulses have been selected to allow interaction with the dominant (3 and 14 ps) kinetic phases of Lumi-R formation. The frequency dependence of the PDP and PRP amplitudes was investigated at 620, 640, 660, and 680 nm, covering excited state absorption (λ(max) = 620 nm), ground state absorption (λ(max) = 660 nm), and stimulated emission (λ(max) = 680 nm) cross sections. Experimental double difference transient absorbance signals (ΔΔOD), from the PDP and PRP measurements, required corrections to remove contributions from ground state repumping. The sensitivity of the resulting ΔΔOD signals was systematically investigated for possible connectivity schemes and photochemical parameters. When applying a homogeneous (sequentially decaying) connectivity scheme in both the 3 and 14 ps kinetic phases, evidence for repumping of an intermediate that has an electronic ground state configuration (GSI) is taken from the dump-induced S1 formation with 620, 640, and 660 nm wavelengths and 1 and 14 ps repump delays. Evidence for repumping a GSI is also seen, for the same excitation wavelengths, when imposing a target connectivity scheme proposed in the literature for the 1 ps repump delay. In contrast, using a 680 nm dump pulse, ground state formation is observed for all models examined. The ΔΔOD signals were dominated by stimulated emission, at both 1 and 14 ps delays for the longer wavelength excitation. The GSI, which is revealed by the PRP measurements and not resolved from pump-probe measurements, is found to be directly formed from the excited state of Pr, and its formation is considered using heterogeneous, homogeneous, and target models to globally fit the data.

Probe into the Elements of Leisure Sports Practice

ERIC Educational Resources Information Center

Li, Kaixian; Gao, Qun

2008-01-01

This paper probes into the basic elements of leisure sports practice by referencing literature materials and logic analyses. Studies show that leisure sports practice consists of six elements, including leisure sports ideas, leisure sports environment, leisure sports time, leisure sports activity, leisure sports skill, and leisure sports state.…

Studies of bio-mimetic medium of ionic and non-ionic micelles by a simple charge transfer fluorescence probe N,N-dimethylaminonapthyl-(acrylo)-nitrile

NASA Astrophysics Data System (ADS)

Samanta, Anuva; Paul, Bijan Kumar; Guchhait, N.

2011-05-01

In this report we have studied micellization process of anionic, cationic and non-ionic surfactants using N,N-dimethylaminonapthyl-(acrylo)-nitrile (DMANAN) as an external fluorescence probe. Micropolarity, microviscosity, critical micellar concentration of these micelles based on steady state absorption and fluorescence and time resolved emission spectroscopy of the probe DMANAN show that the molecule resides in the micelle-water interface for ionic micelles and in the core for the non-ionic micelle. The effect of variation of pH of the micellar solution as well as fluorescence quenching measurements of DMANAN provide further support for the location of the probe in the micelles.

The Cation−π Interaction Enables a Halo-Tag Fluorogenic Probe for Fast No-Wash Live Cell Imaging and Gel-Free Protein Quantification

PubMed Central

2017-01-01

The design of fluorogenic probes for a Halo tag is highly desirable but challenging. Previous work achieved this goal by controlling the chemical switch of spirolactones upon the covalent conjugation between the Halo tag and probes or by incorporating a “channel dye” into the substrate binding tunnel of the Halo tag. In this work, we have developed a novel class of Halo-tag fluorogenic probes that are derived from solvatochromic fluorophores. The optimal probe, harboring a benzothiadiazole scaffold, exhibits a 1000-fold fluorescence enhancement upon reaction with the Halo tag. Structural, computational, and biochemical studies reveal that the benzene ring of a tryptophan residue engages in a cation−π interaction with the dimethylamino electron-donating group of the benzothiadiazole fluorophore in its excited state. We further demonstrate using noncanonical fluorinated tryptophan that the cation−π interaction directly contributes to the fluorogenicity of the benzothiadiazole fluorophore. Mechanistically, this interaction could contribute to the fluorogenicity by promoting the excited-state charge separation and inhibiting the twisting motion of the dimethylamino group, both leading to an enhanced fluorogenicity. Finally, we demonstrate the utility of the probe in no-wash direct imaging of Halo-tagged proteins in live cells. In addition, the fluorogenic nature of the probe enables a gel-free quantification of fusion proteins expressed in mammalian cells, an application that was not possible with previously nonfluorogenic Halo-tag probes. The unique mechanism revealed by this work suggests that incorporation of an excited-state cation−π interaction could be a feasible strategy for enhancing the optical performance of fluorophores and fluorogenic sensors. PMID:28221782

The Cation-π Interaction Enables a Halo-Tag Fluorogenic Probe for Fast No-Wash Live Cell Imaging and Gel-Free Protein Quantification.

PubMed

Liu, Yu; Miao, Kun; Dunham, Noah P; Liu, Hongbin; Fares, Matthew; Boal, Amie K; Li, Xiaosong; Zhang, Xin

2017-03-21

The design of fluorogenic probes for a Halo tag is highly desirable but challenging. Previous work achieved this goal by controlling the chemical switch of spirolactones upon the covalent conjugation between the Halo tag and probes or by incorporating a "channel dye" into the substrate binding tunnel of the Halo tag. In this work, we have developed a novel class of Halo-tag fluorogenic probes that are derived from solvatochromic fluorophores. The optimal probe, harboring a benzothiadiazole scaffold, exhibits a 1000-fold fluorescence enhancement upon reaction with the Halo tag. Structural, computational, and biochemical studies reveal that the benzene ring of a tryptophan residue engages in a cation-π interaction with the dimethylamino electron-donating group of the benzothiadiazole fluorophore in its excited state. We further demonstrate using noncanonical fluorinated tryptophan that the cation-π interaction directly contributes to the fluorogenicity of the benzothiadiazole fluorophore. Mechanistically, this interaction could contribute to the fluorogenicity by promoting the excited-state charge separation and inhibiting the twisting motion of the dimethylamino group, both leading to an enhanced fluorogenicity. Finally, we demonstrate the utility of the probe in no-wash direct imaging of Halo-tagged proteins in live cells. In addition, the fluorogenic nature of the probe enables a gel-free quantification of fusion proteins expressed in mammalian cells, an application that was not possible with previously nonfluorogenic Halo-tag probes. The unique mechanism revealed by this work suggests that incorporation of an excited-state cation-π interaction could be a feasible strategy for enhancing the optical performance of fluorophores and fluorogenic sensors.

Photoswitchable non-fluorescent thermochromic dye-nanoparticle hybrid probes.

PubMed

Harrington, Walter N; Haji, Mwafaq R; Galanzha, Ekaterina I; Nedosekin, Dmitry A; Nima, Zeid A; Watanabe, Fumiya; Ghosh, Anindya; Biris, Alexandru S; Zharov, Vladimir P

2016-11-08

Photoswitchable fluorescent proteins with controllable light-dark states and spectral shifts in emission in response to light have led to breakthroughs in the study of cell biology. Nevertheless, conventional photoswitching is not applicable for weakly fluorescent proteins and requires UV light with low depth penetration in bio-tissue. Here we introduce a novel concept of photoswitchable hybrid probes consisting of thermochromic dye and absorbing nanoparticles, in which temperature-sensitive light-dark states and spectral shifts in absorption can be switched through controllable photothermal heating of doped nanoparticles. The proof-of-concept is demonstrated through the use of two different types of temperature-sensitive dyes doped with magnetic nanoparticles and reversibly photoswitched by a near-infrared laser. Photoacoustic imaging revealed the high contrast of these probes, which is sufficient for their visualization in cells and deep tissue. Our results suggest that these new photoswitchable multicolour probes can be used for multimodal cellular diagnostics and potentially for magnetic and photothermal therapy.

Photoswitchable non-fluorescent thermochromic dye-nanoparticle hybrid probes

NASA Astrophysics Data System (ADS)

Harrington, Walter N.; Haji, Mwafaq R.; Galanzha, Ekaterina I.; Nedosekin, Dmitry A.; Nima, Zeid A.; Watanabe, Fumiya; Ghosh, Anindya; Biris, Alexandru S.; Zharov, Vladimir P.

2016-11-01

Photoswitchable fluorescent proteins with controllable light-dark states and spectral shifts in emission in response to light have led to breakthroughs in the study of cell biology. Nevertheless, conventional photoswitching is not applicable for weakly fluorescent proteins and requires UV light with low depth penetration in bio-tissue. Here we introduce a novel concept of photoswitchable hybrid probes consisting of thermochromic dye and absorbing nanoparticles, in which temperature-sensitive light-dark states and spectral shifts in absorption can be switched through controllable photothermal heating of doped nanoparticles. The proof-of-concept is demonstrated through the use of two different types of temperature-sensitive dyes doped with magnetic nanoparticles and reversibly photoswitched by a near-infrared laser. Photoacoustic imaging revealed the high contrast of these probes, which is sufficient for their visualization in cells and deep tissue. Our results suggest that these new photoswitchable multicolour probes can be used for multimodal cellular diagnostics and potentially for magnetic and photothermal therapy.

Luminescence Probe Studies of Ionomers. I. Steady-State Measurements from Nafion Membrane.

DTIC Science & Technology

1985-02-03

Bu4N+ was monitored by titrating the released protons with NaOH. Bu4N+ uptake by Na+ membranes was assumed to be the same as uptake by acidic form...spaced excited states (21). Because of their solvent sensitivity, 1,5-DNS derivatives may also be used as polarity probes (20). The acid -base... acid . The basic (unprotonated) form of the DNS derivative used here (DA+ ) shows *absorption maxima at ca. 325 and 245 nm (aqueous solution, pH 6.8

Phase decomposition and ordering in Ni-11.3 at.% Ti studied with atom probe tomography.

PubMed

Al-Kassab, T; Kompatscher, M; Kirchheim, R; Kostorz, G; Schönfeld, B

2014-09-01

The decomposition behavior of Ni-rich Ni-Ti was reassessed using Tomographic Atom Probe (TAP) and Laser Assisted Wide Angle Tomographic Atom Probe. Single crystalline specimens of Ni-11.3 at.% Ti were investigated, the states selected from the decomposition path were the metastable γ″ and γ' states introduced on the basis of small-angle neutron scattering (SANS) and the two-phase model for evaluation. The composition values of the precipitates in these states could not be confirmed by APT data as the interface of the ordered precipitates may not be neglected. The present results rather suggest to apply a three-phase model for the interpretation of SANS measurements, in which the width of the interface remains nearly unchanged and the L12 structure close to 3:1 stoichiometry is maintained in the core of the precipitates from the γ″ to the γ' state. Copyright © 2014 Elsevier Ltd. All rights reserved.

A theoretical investigation of two typical two-photon pH fluorescent probes.

PubMed

Xu, Zhong; Ren, Ai-Min; Guo, Jing-Fu; Liu, Xiao-Ting; Huang, Shuang; Feng, Ji-Kang

2013-01-01

Intracellular pH plays an important role in many cellular events, such as cell growth, endocytosis, cell adhesion and so on. Some pH fluorescent probes have been reported, but most of them are one-photon fluorescent probes, studies about two-photon fluorescent probes are very rare. In this work, the geometrical structure, electronic structure and one-photon properties of a series of two-photon pH fluorescent probes have been theoretically studied by using density functional theory (DFT) method. Their two-photon absorption (TPA) properties are calculated using the method of ZINDO/sum-over-states method. Two types of two-photon pH fluorescent probes have been investigated by theoretical methods. The mechanisms of the Photoinduced Charge Transfer (PCT) probes and the Photoinduced Electron Transfer (PET) probes are verified specifically. Some designed strategies of good two-photon pH fluorescent probes are suggested on the basis of the investigated results of two mechanisms. For the PCT probes, substituting a stronger electron-donating group for the terminal methoxyl group is an advisable choice to increase the TPA cross section. For the PET probes, the TPA cross sections increase upon protonation. © 2012 Wiley Periodicals, Inc. Photochemistry and Photobiology © 2012 The American Society of Photobiology.

X-ray Pump–Probe Investigation of Charge and Dissociation Dynamics in Methyl Iodine Molecule

DOE PAGES

Fang, Li; Xiong, Hui; Kukk, Edwin; ...

2017-05-19

Molecular dynamics is of fundamental interest in natural science research. The capability of investigating molecular dynamics is one of the various motivations for ultrafast optics. Here, we present our investigation of photoionization and nuclear dynamics in methyl iodine (CH 3I) molecule with an X-ray pump X-ray probe scheme. The pump–probe experiment was realized with a two-mirror X-ray split and delay apparatus. Time-of-flight mass spectra at various pump–probe delay times were recorded to obtain the time profile for the creation of high charge states via sequential ionization and for molecular dissociation. We observed high charge states of atomic iodine up tomore » 29+, and visualized the evolution of creating these high atomic ion charge states, including their population suppression and enhancement as the arrival time of the second X-ray pulse was varied. We also show the evolution of the kinetics of the high charge states upon the timing of their creation during the ionization-dissociation coupled dynamics. We demonstrate the implementation of X-ray pump–probe methodology for investigating X-ray induced molecular dynamics with femtosecond temporal resolution. The results indicate the footprints of ionization that lead to high charge states, probing the long-range potential curves of the high charge states.« less

Supramolecular Amino Acid Based Hydrogels: Probing the Contribution of Additive Molecules using NMR Spectroscopy

PubMed Central

Ramalhete, Susana M.; Nartowski, Karol P.; Sarathchandra, Nichola; Foster, Jamie S.; Round, Andrew N.; Angulo, Jesús

2017-01-01

Abstract Supramolecular hydrogels are composed of self‐assembled solid networks that restrict the flow of water. l‐Phenylalanine is the smallest molecule reported to date to form gel networks in water, and it is of particular interest due to its crystalline gel state. Single and multi‐component hydrogels of l‐phenylalanine are used herein as model materials to develop an NMR‐based analytical approach to gain insight into the mechanisms of supramolecular gelation. Structure and composition of the gel fibres were probed using PXRD, solid‐state NMR experiments and microscopic techniques. Solution‐state NMR studies probed the properties of free gelator molecules in an equilibrium with bound molecules. The dynamics of exchange at the gel/solution interfaces was investigated further using high‐resolution magic angle spinning (HR‐MAS) and saturation transfer difference (STD) NMR experiments. This approach allowed the identification of which additive molecules contributed in modifying the material properties. PMID:28401991

Are you mind-wandering, or is your mind on task? The effect of probe framing on mind-wandering reports.

PubMed

Weinstein, Yana; De Lima, Henry J; van der Zee, Tim

2018-04-01

The last decade has seen a dramatic rise in the number of studies that utilize the probe-caught method of collecting mind-wandering reports. This method involves stopping participants during a task, presenting them with a thought probe, and asking them to choose the appropriate report option to describe their thought-state. In this experiment we manipulated the framing of this probe, and demonstrated a substantial difference in mind-wandering reports as a function of whether the probe was presented in a mind-wandering frame compared with an on-task frame. This framing effect has implications both for interpretations of existing data and for methodological choices made by researchers who use the probe-caught mind-wandering paradigm.

Experimental Studies of the Effect of Intent Information on Cockpit Traffic Displays

NASA Technical Reports Server (NTRS)

Barhydt, Richard; Hansman, R. John

1997-01-01

Intent information provides knowledge of another aircraft's current and future trajectory states. Prototype traffic displays were designed for four different levels of intent: Position, Rate, Commanded State, and FMS (Flight Management System)-Path. The current TCAS (traffic collision avoidance systems) Display, which shows altitude rate in addition to current position and altitude, was used as a baseline and represents the lowest level of intent. The Rate, Commanded State, and FMS-Path Displays show increasing levels of intent information using TCAS-like symbology in addition to incorporating a conflict probe and profile view display. An initial experiment was run on the MIT (Massachusetts Institute of Technology) Part Task Flight Simulator in which eight airline pilots flew five traffic scenarios with each of the four displays. Results show that pilots had fewer separation violations and maneuvered earlier with the three intent displays. Separation violations were reduced when pilots maneuvered earlier. A second experiment was run to compare performance between displaying intent information directly and incorporating it into a conflict probe. A different set of eight airline pilots flew four traffic scenarios with the TCAS and Commanded State Displays with and without the conflict probe. Conflict probes with two minute and long range look-ahead times were tested. Displaying conflict bands or showing intent information directly both led to fewer separation violations and earlier avoidance maneuvers than the base TCAS Display. Performance was similar between the two minute and long range look-ahead conflict probes. Pilots preferred all intent displays over the TCAS Display.

Recent advances in high-performance fluorescent and bioluminescent RNA imaging probes.

PubMed

Xia, Yuqiong; Zhang, Ruili; Wang, Zhongliang; Tian, Jie; Chen, Xiaoyuan

2017-05-22

RNA plays an important role in life processes. Imaging of messenger RNAs (mRNAs) and micro-RNAs (miRNAs) not only allows us to learn the formation and transcription of mRNAs and the biogenesis of miRNAs involved in various life processes, but also helps in detecting cancer. High-performance RNA imaging probes greatly expand our view of life processes and enhance the cancer detection accuracy. In this review, we summarize the state-of-the-art high-performance RNA imaging probes, including exogenous probes that can image RNA sequences with special modification and endogeneous probes that can directly image endogenous RNAs without special treatment. For each probe, we review its structure and imaging principle in detail. Finally, we summarize the application of mRNA and miRNA imaging probes in studying life processes as well as in detecting cancer. By correlating the structures and principles of various probes with their practical uses, we compare different RNA imaging probes and offer guidance for better utilization of the current imaging probes and the future design of higher-performance RNA imaging probes.

A model Ni-Al-Mo superalloy studied by ultraviolet pulsed-laser-assisted local-electrode atom-probe tomography.

PubMed

Tu, Yiyou; Plotnikov, Elizaveta Y; Seidman, David N

2015-04-01

This study investigates the effects of the charge-state ratio of evaporated ions on the accuracy of local-electrode atom-probe (LEAP) tomographic compositional and structural analyses, which employs a picosecond ultraviolet pulsed laser. Experimental results demonstrate that the charge-state ratio is a better indicator of the best atom-probe tomography (APT) experimental conditions compared with laser pulse energy. The thermal tails in the mass spectra decrease significantly, and the mass resolving power (m/Δm) increases by 87.5 and 185.7% at full-width half-maximum and full-width tenth-maximum, respectively, as the laser pulse energy is increased from 5 to 30 pJ/pulse. The measured composition of this alloy depends on the charge-state ratio of the evaporated ions, and the most accurate composition is obtained when Ni2+/Ni+ is in the range of 0.3-20. The γ(f.c.c.)/γ'(L12) interface is quantitatively more diffuse when determined from the measured concentration profiles for higher laser pulse energies. Conclusions of the APT compositional and structural analyses utilizing the same suitable charge-state ratio are more comparable than those collected with the same laser pulse energy.

Spin-orbit-coupled fermions in an optical lattice clock

NASA Astrophysics Data System (ADS)

Kolkowitz, S.; Bromley, S. L.; Bothwell, T.; Wall, M. L.; Marti, G. E.; Koller, A. P.; Zhang, X.; Rey, A. M.; Ye, J.

2017-02-01

Engineered spin-orbit coupling (SOC) in cold-atom systems can enable the study of new synthetic materials and complex condensed matter phenomena. However, spontaneous emission in alkali-atom spin-orbit-coupled systems is hindered by heating, limiting the observation of many-body effects and motivating research into potential alternatives. Here we demonstrate that spin-orbit-coupled fermions can be engineered to occur naturally in a one-dimensional optical lattice clock. In contrast to previous SOC experiments, here the SOC is both generated and probed using a direct ultra-narrow optical clock transition between two electronic orbital states in 87Sr atoms. We use clock spectroscopy to prepare lattice band populations, internal electronic states and quasi-momenta, and to produce spin-orbit-coupled dynamics. The exceptionally long lifetime of the excited clock state (160 seconds) eliminates decoherence and atom loss from spontaneous emission at all relevant experimental timescales, allowing subsequent momentum- and spin-resolved in situ probing of the SOC band structure and eigenstates. We use these capabilities to study Bloch oscillations, spin-momentum locking and Van Hove singularities in the transition density of states. Our results lay the groundwork for using fermionic optical lattice clocks to probe new phases of matter.

Probing the non-locality of Majorana fermions via quantum correlations

PubMed Central

Li, Jun; Yu, Ting; Lin, Hai-Qing; You, J. Q.

2014-01-01

Majorana fermions (MFs) are exotic particles that are their own anti-particles. Recently, the search for the MFs occurring as quasi-particle excitations in solid-state systems has attracted widespread interest, because of their fundamental importance in fundamental physics and potential applications in topological quantum computation based on solid-state devices. Here we study the quantum correlations between two spatially separate quantum dots induced by a pair of MFs emerging at the two ends of a semiconductor nanowire, in order to develop a new method for probing the MFs. We find that without the tunnel coupling between these paired MFs, quantum entanglement cannot be induced from an unentangled (i.e., product) state, but quantum discord is observed due to the intrinsic nonlocal correlations of the paired MFs. This finding reveals that quantum discord can indeed demonstrate the intrinsic non-locality of the MFs formed in the nanowire. Also, quantum discord can be employed to discriminate the MFs from the regular fermions. Furthermore, we propose an experimental setup to measure the onset of quantum discord due to the nonlocal correlations. Our approach provides a new, and experimentally accessible, method to study the Majorana bound states by probing their intrinsic non-locality signature. PMID:24816484

Line Intensity Mapping during the Epoch of Reionization

NASA Astrophysics Data System (ADS)

Silva, Marta B.; Zaroubi, Saleem

2018-05-01

Characterizing the properties and the evolution of the first stars and galaxies is a challenging task for traditional galaxy surveys since they are sensitivity limited and can only detect the brightest light sources. Three-dimensional intensity mapping (IM) of transition lines can be a valuable alternative to study the high redshift Universe given that this technique avoids sensitivity limitation problems by measuring the overall emission of a line, with a low resolution, without resolving its sources. While 21cm line IM surveys probe neutral hydrogen gas and can, therefore, be used to probe the state of the IGM and the evolution of the ionization field during the Epoch of Reionization (EoR). IM surveys of other lines, such as CO, CII, Ly-alpha or H-alpha, can be used to probe the galaxies which emitted most of the ionizing radiation responsible for the EoR. These lines will trace the different ISM gas phases, the excitation state of this gas, its metallicity, etc. This study addresses IM of multiple transition lines and how it can be used to probe the EoR and to constrain the redshift evolution of galaxy properties.

AIE active multianalyte fluorescent probe for the detection of Cu2+, Ni2+ and Hg2+ ions.

PubMed

Pannipara, Mehboobali; Al-Sehemi, Abdullah G; Irfan, Ahmad; Assiri, Mohammed; Kalam, Abul; Al-Ammari, Yahya S

2018-08-05

A novel pyrazolyl chromene derivative (Probe 1) displaying aggregation induced emission (AIE) properties that capable of sensing of multiple metal ions has been designed and synthesized. The multi analyte probe exhibits selective sensing for Cu 2+ and Ni 2+ ions via fluorescence turn-off mechanism and ratiometric selectivity for Hg 2+ ions in aqueous media. The extent of binding of the probe with sensitive metal ions has been demonstrated. The experimental results were further investigated by computational means by optimizing the ground state geometries of Probe 1 and its various metal complexes for Probe 1-Ni, Probe 1-Hg and Probe 1-Cu using density functional theory (DFT) at B3LYP/6-31+g(d,p) (LANL2DZ) level. On the basis of binding energies, the stability of metal complexes has been studied. In Probe 1-Ni and Probe 1-Cu complexes, charge transfer has been observed from Probe 1 to metal ions revealing ligand to metal charge transfer (LMCT) while in Probe1-Hg complex LMCT as well as intra-molecular charge tranfer (ICT) within Probe 1. Copyright © 2018 Elsevier B.V. All rights reserved.

Vibrational wave packet dynamics in NaK: The A 1Σ+ state

NASA Astrophysics Data System (ADS)

Andersson, L. Mauritz; Karlsson, Hans O.; Goscinski, Osvaldo; Berg, Lars-Erik; Beutter, Matthias; Hansson, Tony

1999-02-01

A combined experimental and theoretical study of the vibrational wave packet dynamics for the NaK molecule in the A 1Σ+ state is presented. The experiment utilises a 790 nm one-colour femtosecond pump-probe scheme with detection of a previously not reported dissociation pathway of the 3 1Π+ state, leading to the Na(3p)+K(4s) product channel. The dissociation is suggested to proceed via either collisionally mediated processes or a molecular cascading process via the 4 1Σ+ state, which crosses several states correlating to the Na(3p)+K(4s) limit. Time-dependent quantum mechanical calculations are used for studying the dynamics in detail. Simulations are performed both for 790 nm and for 766 nm, to relate also to earlier studies. The previous interpretations of the probe processes are revised. Inclusion of vibrational and rotational temperature effects are shown to be crucial for explaining the shape of the signal and the vibrational period, and leads to excellent agreement with the experiments.

Superiorities of time-correlated single-photon counting against standard fluorimetry in exploiting the potential of fluorochromized oligonucleotide probes for biomedical investigation

NASA Astrophysics Data System (ADS)

Lamperti, Marco; Nardo, Luca; Bondani, Maria

2015-05-01

Site-specific fluorescence-resonance-energy-transfer donor-acceptor dual-labelled oligonucleotide probes are widely used in state-of-art biotechnological applications. Such applications include their usage as primers in polymerase chain reaction. However, the steady-state fluorescence intensity signal emitted by these molecular tools strongly depends from the specificities of the probe conformation. For this reason, the information which can be reliably inferred by steady-state fluorimetry performed on such samples is forcedly confined to a semi-qualitative level. Namely, fluorescent emission is frequently used as ON/OFF indicator of the probe hybridization state, i.e. detection of fluorescence signals indicates either hybridization to or detachment from the template DNA of the probe. Nonetheless, a fully quantitative analysis of their fluorescence emission properties would disclose other exciting applications of dual-labelled probes in biosensing. Here we show how time-correlated single-photon counting can be applied to get rid of the technical limitations and interpretational ambiguities plaguing the intensity analysis, and to derive information on the template DNA reaching single-base.

Sound intensity probe for ultrasonic field in water using light-emitting diodes and piezoelectric elements

NASA Astrophysics Data System (ADS)

Zeng, Xi; Mizuno, Yosuke; Nakamura, Kentaro

2017-12-01

The sound intensity vector provides useful information on the state of an ultrasonic field in water, since sound intensity is a vector quantity expressing the direction and magnitude of the sound field. In the previous studies on sound intensity measurement in water, conventional piezoelectric sensors and metal cables were used, and the transmission distance was limited. A new configuration of a sound intensity probe suitable for ultrasonic measurement in water is proposed and constructed for trial in this study. The probe consists of light-emitting diodes and piezoelectric elements, and the output signals are transmitted through fiber optic cables as intensity-modulated light. Sound intensity measurements of a 26 kHz ultrasonic field in water are demonstrated. The difference in the intensity vector state between the water tank with and without sound-absorbing material on its walls was successfully observed.

Solid-state electrochemistry on the nanometer and atomic scales: the scanning probe microscopy approach

DOE PAGES

Strelcov, Evgheni; Yang, Sang Mo; Jesse, Stephen; ...

2016-04-21

Energy technologies of the 21st century require an understanding and precise control over ion transport and electrochemistry at all length scales – from single atoms to macroscopic devices. Our short review provides a summary of recent studies dedicated to methods of advanced scanning probe microscopy for probing electrochemical transformations in solids at the meso-, nano- and atomic scales. In this discussion we present the advantages and limitations of several techniques and a wealth of examples highlighting peculiarities of nanoscale electrochemistry.

Solvatochromic and Fluorogenic Dyes as Environment-Sensitive Probes: Design and Biological Applications.

PubMed

Klymchenko, Andrey S

2017-02-21

Fluorescent environment-sensitive probes are specially designed dyes that change their fluorescence intensity (fluorogenic dyes) or color (e.g., solvatochromic dyes) in response to change in their microenvironment polarity, viscosity, and molecular order. The studies of the past decade, including those of our group, have shown that these molecules become universal tools in fluorescence sensing and imaging. In fact, any biomolecular interaction or change in biomolecular organization results in modification of the local microenvironment, which can be directly monitored by these types of probes. In this Account, the main examples of environment-sensitive probes are summarized according to their design concepts. Solvatochromic dyes constitute a large class of environment-sensitive probes which change their color in response to polarity. Generally, they are push-pull dyes undergoing intramolecular charge transfer. Emission of their highly polarized excited state shifts to the red in more polar solvents. Excited-state intramolecular proton transfer is the second key concept to design efficient solvatochromic dyes, which respond to the microenvironment by changing relative intensity of the two emissive tautomeric forms. Due to their sensitivity to polarity and hydration, solvatochromic dyes have been successfully applied to biological membranes for studying lipid domains (rafts), apoptosis and endocytosis. As fluorescent labels, solvatochromic dyes can detect practically any type of biomolecular interactions, involving proteins, nucleic acids and biomembranes, because the binding event excludes local water molecules from the interaction site. On the other hand, fluorogenic probes usually exploit intramolecular rotation (conformation change) as a design concept, with molecular rotors being main representatives. These probes were particularly efficient for imaging viscosity and lipid order in biomembranes as well as to light up biomolecular targets, such as antibodies, aptamers and receptors. The emerging concepts to achieve fluorogenic response to the microenvironment include ground-state isomerization, aggregation-caused quenching, and aggregation-induced emission. The ground-state isomerization exploits, for instance, polarity-dependent spiro-lactone formation in silica-rhodamines. The aggregation-caused quenching uses disruption of the self-quenched dimers and nanoassemblies of dyes in less polar environments of lipid membranes and biomolecules. The aggregation-induced emission couples target recognition with formation of highly fluorescent dye aggregates. Overall, solvatochromic and fluorogenic probes enable background-free bioimaging in wash-free conditions as well as quantitative analysis when combined with advanced microscopy, such as fluorescence lifetime (FLIM) and ratiometric imaging. Further development of fluorescent environment-sensitive probes should address some remaining problems: (i) improving their optical properties, especially brightness, photostability, and far-red to near-infrared operating range; (ii) minimizing nonspecific interactions of the probes in biological systems; (iii) their adaptation for advanced microscopies, notably for superresolution and in vivo imaging.

Automated system for periodontal disease diagnosis

NASA Astrophysics Data System (ADS)

Albalat, Salvador E.; Alcaniz-Raya, Mariano L.; Juan, M. Carmen; Grau Colomer, Vincente; Monserrat, Carlos

1997-04-01

Evolution of periodontal disease is one of the most important data for the clinicians in order to achieve correct planning and treatment. Clinical measure of the periodontal sulcus depth is the most important datum to know the exact state of periodontal disease. These measures must be done periodically study bone resorption evolution around teeth. Time factor of resorption indicates aggressiveness of periodontitis. Manual probes are commonly used with direct reading. Mechanical probes give automatic signal but this method uses complicated and heavy probes that are only limited for University researchers. Probe position must be the same to have right diagnosis. Digital image analysis of periodontal probing provides practical, accurate and easy tool. Gum and plaque index could also be digitally measured with this method.

Fluorescent probes for lipid rafts: from model membranes to living cells.

PubMed

Klymchenko, Andrey S; Kreder, Rémy

2014-01-16

Membrane microdomains (rafts) remain one of the controversial issues in biophysics. Fluorescent molecular probes, which make these lipid nanostructures visible through optical techniques, are one of the tools currently used to study lipid rafts. The most common are lipophilic fluorescent probes that partition specifically into liquid ordered or liquid disordered phase. Their partition depends on the lipid composition of a given phase, which complicates their use in cellular membranes. A second class of probes is based on environment-sensitive dyes, which partition into both phases, but stain them by different fluorescence color, intensity, or lifetime. These probes can directly address the properties of each separate phase, but their cellular applications are still limited. The present review focuses on summarizing the current state in the field of developing and applying fluorescent molecular probes to study lipid rafts. We highlight an urgent need to develop new probes, specifically adapted for cell plasma membranes and compatible with modern fluorescence microscopy techniques to push the understanding of membrane microdomains forward. Copyright © 2014 Elsevier Ltd. All rights reserved.

Highly Selective Relaxation of the OH Stretching Overtones in Isolated HDO Molecules Observed by Infrared Pump-Repump-Probe Spectroscopy.

PubMed

Hutzler, Daniel; Werhahn, Jasper C; Heider, Rupert; Bradler, Maximilian; Kienberger, Reinhard; Riedle, Eberhard; Iglev, Hristo

2015-07-02

A quantitative investigation of the relaxation dynamics of higher-lying vibrational states is afforded by a novel method of infrared pump-repump-probe spectroscopy. The technique is used to study the dynamics of OH stretching overtones in NaClO4·HDO monohydrate. We observe a continuous decrease of the energy separation for the first four states, i.e. v01 = 3575 cm(-1), v12 = 3370 cm(-1), and v23 = 3170 cm(-1), respectively. The population lifetime of the first excited state is 7.2 ps, while the one of the second excited state is largely reduced to 1.4 ps. The relaxation of the v = 2 state proceeds nearly quantitatively to the v = 1 state. The new information on the OH stretching overtones demands improved theoretical potentials and modeling of the H bond interactions. This work shows the potential of the new technique for the precise study of complex vibrational relaxation pathways.

"Gap hunting" to characterize clustered probe signals in Illumina methylation array data.

PubMed

Andrews, Shan V; Ladd-Acosta, Christine; Feinberg, Andrew P; Hansen, Kasper D; Fallin, M Daniele

2016-01-01

The Illumina 450k array has been widely used in epigenetic association studies. Current quality-control (QC) pipelines typically remove certain sets of probes, such as those containing a SNP or with multiple mapping locations. An additional set of potentially problematic probes are those with DNA methylation distributions characterized by two or more distinct clusters separated by gaps. Data-driven identification of such probes may offer additional insights for downstream analyses. We developed a procedure, termed "gap hunting," to identify probes showing clustered distributions. Among 590 peripheral blood samples from the Study to Explore Early Development, we identified 11,007 "gap probes." The vast majority (9199) are likely attributed to an underlying SNP(s) or other variant in the probe, although SNP-affected probes exist that do not produce a gap signals. Specific factors predict which SNPs lead to gap signals, including type of nucleotide change, probe type, DNA strand, and overall methylation state. These expected effects are demonstrated in paired genotype and 450k data on the same samples. Gap probes can also serve as a surrogate for the local genetic sequence on a haplotype scale and can be used to adjust for population stratification. The characteristics of gap probes reflect potentially informative biology. QC pipelines may benefit from an efficient data-driven approach that "flags" gap probes, rather than filtering such probes, followed by careful interpretation of downstream association analyses. Our results should translate directly to the recently released Illumina EPIC array given the similar chemistry and content design.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fang, Li; Xiong, Hui; Kukk, Edwin

Molecular dynamics is of fundamental interest in natural science research. The capability of investigating molecular dynamics is one of the various motivations for ultrafast optics. Here, we present our investigation of photoionization and nuclear dynamics in methyl iodine (CH 3I) molecule with an X-ray pump X-ray probe scheme. The pump–probe experiment was realized with a two-mirror X-ray split and delay apparatus. Time-of-flight mass spectra at various pump–probe delay times were recorded to obtain the time profile for the creation of high charge states via sequential ionization and for molecular dissociation. We observed high charge states of atomic iodine up tomore » 29+, and visualized the evolution of creating these high atomic ion charge states, including their population suppression and enhancement as the arrival time of the second X-ray pulse was varied. We also show the evolution of the kinetics of the high charge states upon the timing of their creation during the ionization-dissociation coupled dynamics. We demonstrate the implementation of X-ray pump–probe methodology for investigating X-ray induced molecular dynamics with femtosecond temporal resolution. The results indicate the footprints of ionization that lead to high charge states, probing the long-range potential curves of the high charge states.« less

Photoionization of NaK molecule with a double-well potential in femtosecond pump probe pulse laser fields

NASA Astrophysics Data System (ADS)

Yu, Jie; Wang, Sen-Ming; Yuan, Kai-Jun; Cong, Shu-Lin

2006-09-01

The method of time-dependent quantum wave packet dynamics is used to calculate the femtosecond pump-probe photoelectron spectra and study the wave packet dynamic processes of the double-minimum potential state 61Σ+ of NaK in intense laser fields. The evolutions of the wave packet and the photoelectron energy spectra with time and internuclear distance are described in detail. The wave packet dynamic information of the 61Σ+ state can be extracted from the photoelectron energy spectra.

AUTOFLUORESCENCE IN PRIMARY RAINBOW TROUT HEPATOCYTES INTERFERES WITH MEASUREMENT OF OXIDATIVE ACTIVITY VIA THE EXOGENOUS PROBE, DCF, BUT PROVIDES INTRINSIC MEASURE OF CELLULAR OXIDATIVE STATE

EPA Science Inventory

The compound 2', 7'-dichlorodihydrofluoroscein diacetate is a probe commonly used to detect oxidative activity in live cells. Studies were undertaken to measure reactive oxygen species generated in freshly isolated rainbow trout hepatocytes exposed to a variety of redox cycling c...

Modular Rake of Pitot Probes

NASA Technical Reports Server (NTRS)

Dunlap, Timothy A.; Henry, Michael W.; Homyk, Raymond P.

2004-01-01

The figure presents selected views of a modular rake of 17 pitot probes for measuring both transient and steady-state pressures in a supersonic wind tunnel. In addition to pitot tubes visible in the figure, the probe modules contain (1) high-frequency dynamic-pressure transducers connected through wires to remote monitoring circuitry and (2) flow passages that lead to tubes that, in turn, lead to remote steady-state pressure transducers. Prior pitot-probe rakes were fabricated as unitary structures, into which the individual pitot probes were brazed. Repair or replacement of individual probes was difficult, costly, and time-consuming because (1) it was necessary to remove entire rakes in order to unbraze individual malfunctioning probes and (2) the heat of unbrazing a failed probe and of brazing a new probe in place could damage adjacent probes. In contrast, the modules in the present probe are designed to be relatively quickly and easily replaceable with no heating and, in many cases, without need for removal of the entire rake from the wind tunnel. To remove a malfunctioning probe, one first removes a screw-mounted V-cross-section cover that holds the probe and adjacent probes in place. Then one removes a screw-mounted cover plate to gain access to the steady-state pressure tubes and dynamicpressure wires. Next, one disconnects the tube and wires of the affected probe. Finally, one installs a new probe in the reverse of the aforementioned sequence. The wire connections can be made by soldering, but to facilitate removal and installation, they can be made via miniature plugs and sockets. The connections between the probe flow passages and the tubes leading to the remote pressure sensors can be made by use of any of a variety of readily available flexible tubes that can be easily pulled off and slid back on for removal and installation, respectively.

Time-resolved multi-mass ion imaging: Femtosecond UV-VUV pump-probe spectroscopy with the PImMS camera.

PubMed

Forbes, Ruaridh; Makhija, Varun; Veyrinas, Kévin; Stolow, Albert; Lee, Jason W L; Burt, Michael; Brouard, Mark; Vallance, Claire; Wilkinson, Iain; Lausten, Rune; Hockett, Paul

2017-07-07

The Pixel-Imaging Mass Spectrometry (PImMS) camera allows for 3D charged particle imaging measurements, in which the particle time-of-flight is recorded along with (x, y) position. Coupling the PImMS camera to an ultrafast pump-probe velocity-map imaging spectroscopy apparatus therefore provides a route to time-resolved multi-mass ion imaging, with both high count rates and large dynamic range, thus allowing for rapid measurements of complex photofragmentation dynamics. Furthermore, the use of vacuum ultraviolet wavelengths for the probe pulse allows for an enhanced observation window for the study of excited state molecular dynamics in small polyatomic molecules having relatively high ionization potentials. Herein, preliminary time-resolved multi-mass imaging results from C 2 F 3 I photolysis are presented. The experiments utilized femtosecond VUV and UV (160.8 nm and 267 nm) pump and probe laser pulses in order to demonstrate and explore this new time-resolved experimental ion imaging configuration. The data indicate the depth and power of this measurement modality, with a range of photofragments readily observed, and many indications of complex underlying wavepacket dynamics on the excited state(s) prepared.

Carbon-Based Solid-State Calcium Ion-Selective Microelectrode and Scanning Electrochemical Microscopy: A Quantitative Study of pH-Dependent Release of Calcium Ions from Bioactive Glass.

PubMed

Ummadi, Jyothir Ganesh; Downs, Corey J; Joshi, Vrushali S; Ferracane, Jack L; Koley, Dipankar

2016-03-15

Solid-state ion-selective electrodes are used as scanning electrochemical microscope (SECM) probes because of their inherent fast response time and ease of miniaturization. In this study, we report the development of a solid-state, low-poly(vinyl chloride), carbon-based calcium ion-selective microelectrode (Ca(2+)-ISME), 25 μm in diameter, capable of performing an amperometric approach curve and serving as a potentiometric sensor. The Ca(2+)-ISME has a broad linear response range of 5 μM to 200 mM with a near Nernstian slope of 28 mV/log[a(Ca(2+))]. The calculated detection limit for Ca(2+)-ISME is 1 μM. The selectivity coefficients of this Ca(2+)-ISME are log K(Ca(2+),A) = -5.88, -5.54, and -6.31 for Mg(2+), Na(+), and K(+), respectively. We used this new type of Ca(2+)-ISME as an SECM probe to quantitatively map the chemical microenvironment produced by a model substrate, bioactive glass (BAG). In acidic conditions (pH 4.5), BAG was found to increase the calcium ion concentration from 0.7 mM ([Ca(2+)] in artificial saliva) to 1.4 mM at 20 μm above the surface. In addition, a solid-state dual SECM pH probe was used to correlate the release of calcium ions with the change in local pH. Three-dimensional pH and calcium ion distribution mapping were also obtained by using these solid-state probes. The quantitative mapping of pH and Ca(2+) above the BAG elucidates the effectiveness of BAG in neutralizing and releasing calcium ions in acidic conditions.

Three-dimensional spectroscopy of vibrational energy in liquids: nitromethane and acetonitrile.

PubMed

Sun, Yuxiao; Pein, Brandt C; Dlott, Dana D

2013-12-12

We introduce a novel type of three-dimensional (3D) spectroscopy to study vibrational energy transfer, where an IR pulse tunable through the CH-stretching and CD-stretching regions was used to create parent vibrational excitations in liquids and a visible probe pulse was used to generate both Stokes and anti-Stokes Raman spectra as a function of delay time. The Raman spectra determine how much vibrational excitation was present in each probed state. The three dimensions are the wavenumber of the pumped state, the wavenumber of the probed state, and the time interval. The technique was used to study nitromethane (NM) and acetonitrile (ACN) and their deuterated analogues at ambient temperature. The 3D spectra were quite complicated. Three types of artifacts due to nonlinear light scattering were observed. Along the diagonal were two fundamental CH-stretch (or CD-stretch) transitions and several weaker combination bands or overtone transitions. Because Raman spectroscopy allows us to simultaneously probe a wide wavenumber region, for every diagonal peak, there were ∼10 off-diagonal peaks. The cross-peaks at shorter delay times reveal the nature of the initial excitation by showing which lower-wavenumber excitations were produced along with the pumped CH-stretch or CD-stretch. The longer-time spectra characterized vibrational energy relaxation processes, and showed how daughter vibrations were generated by different parent excitations.

Following coherent multichannel nuclear wave packets in pump-probe studies of O2 with ultrashort laser pulses

NASA Astrophysics Data System (ADS)

Xue, Shan; Du, Hongchuan; Hu, Bitao; Lin, C. D.; Le, Anh-Thu

2018-04-01

We reexamine the recent pump-probe experiment with O2 using short intense infrared laser pulses theoretically. Using parameters that closely mimic the experimental conditions and taking into account the angle-dependent population redistribution due to resonant coupling between the relevant states, we show that the observed kinetic energy release spectra, including the energy-dependent structure and the quantum beat frequencies, can be accurately reproduced. Our results reveal additional important channels that were missed earlier. In particular, the strong contributions from O2+a 4Πu and b 4Σg- states lead to the possibility of observing the interchannel beating. We further demonstrate that, by varying the laser parameters, the coherent nuclear wave-packet motions on different potential energy surfaces (PESs) can be probed and the properties of the PES can be examined. Future experiments with different wavelength lasers are proposed for better probing and controlling nuclear dynamics on different PESs.

Photoswitchable non-fluorescent thermochromic dye-nanoparticle hybrid probes

PubMed Central

Harrington, Walter N.; Haji, Mwafaq R.; Galanzha, Ekaterina I.; Nedosekin, Dmitry A.; Nima, Zeid A.; Watanabe, Fumiya; Ghosh, Anindya; Biris, Alexandru S.; Zharov, Vladimir P.

2016-01-01

Photoswitchable fluorescent proteins with controllable light–dark states and spectral shifts in emission in response to light have led to breakthroughs in the study of cell biology. Nevertheless, conventional photoswitching is not applicable for weakly fluorescent proteins and requires UV light with low depth penetration in bio-tissue. Here we introduce a novel concept of photoswitchable hybrid probes consisting of thermochromic dye and absorbing nanoparticles, in which temperature-sensitive light–dark states and spectral shifts in absorption can be switched through controllable photothermal heating of doped nanoparticles. The proof-of-concept is demonstrated through the use of two different types of temperature-sensitive dyes doped with magnetic nanoparticles and reversibly photoswitched by a near-infrared laser. Photoacoustic imaging revealed the high contrast of these probes, which is sufficient for their visualization in cells and deep tissue. Our results suggest that these new photoswitchable multicolour probes can be used for multimodal cellular diagnostics and potentially for magnetic and photothermal therapy. PMID:27824110

Discrimination of three types of homopolymers in single-stranded DNA with solid-state nanopores through external control of the DNA motion.

PubMed

Akahori, Rena; Yanagi, Itaru; Goto, Yusuke; Harada, Kunio; Yokoi, Takahide; Takeda, Ken-Ichi

2017-08-22

To achieve DNA sequencing with solid-state nanopores, the speed of the DNA in the nanopore must be controlled to obtain sequence-specific signals. In this study, we fabricated a nanopore-sensing system equipped with a DNA motion controller. DNA strands were immobilized on a Si probe, and approach of this probe to the nanopore vicinity could be controlled using a piezo actuator and stepper motor. The area of the Si probe was larger than the area of the membrane, which meant that the immobilized DNA could enter the nanopore without the need for the probe to scan to determine the location of the nanopore in the membrane. We demonstrated that a single-stranded DNA could be inserted into and removed from a nanopore in our experimental system. The number of different ionic-current levels observed while DNA remained in the nanopore corresponded to the number of different types of homopolymers in the DNA.

Quasiparticle Interference Studies of Quantum Materials.

PubMed

Avraham, Nurit; Reiner, Jonathan; Kumar-Nayak, Abhay; Morali, Noam; Batabyal, Rajib; Yan, Binghai; Beidenkopf, Haim

2018-06-03

Exotic electronic states are realized in novel quantum materials. This field is revolutionized by the topological classification of materials. Such compounds necessarily host unique states on their boundaries. Scanning tunneling microscopy studies of these surface states have provided a wealth of spectroscopic characterization, with the successful cooperation of ab initio calculations. The method of quasiparticle interference imaging proves to be particularly useful for probing the dispersion relation of the surface bands. Herein, how a variety of additional fundamental electronic properties can be probed via this method is reviewed. It is demonstrated how quasiparticle interference measurements entail mesoscopic size quantization and the electronic phase coherence in semiconducting nanowires; helical spin protection and energy-momentum fluctuations in a topological insulator; and the structure of the Bloch wave function and the relative insusceptibility of topological electronic states to surface potential in a topological Weyl semimetal. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Optimal control theory with continuously distributed target states: An application to NaK

NASA Astrophysics Data System (ADS)

Kaiser, Andreas; May, Volkhard

2006-01-01

Laser pulse control of molecular dynamics is studied theoretically by using optimal control theory. The control theory is extended to target states which are distributed in time as well as in a space of parameters which are responsible for a change of individual molecular properties. This generalized treatment of a control task is first applied to wave packet formation in randomly oriented diatomic systems. Concentrating on an ensemble of NaK molecules which are not aligned the control yield decreases drastically when compared with an aligned ensemble. Second, we demonstrate for NaK the maximization of the probe pulse transient absorption in a pump-probe scheme with an optimized pump pulse. These computations suggest an overall optical control scheme, whereby a flexible technique is suggested to form particular wave packets in the excited state potential energy surface. In particular, it is shown that considerable wave packet localization at the turning points of the first-excited Σ-state potential energy surfaces of NaK may be achieved. The dependency of the control yield on the probe pulse parameters is also discussed.

Versatile Gaussian probes for squeezing estimation

NASA Astrophysics Data System (ADS)

Rigovacca, Luca; Farace, Alessandro; Souza, Leonardo A. M.; De Pasquale, Antonella; Giovannetti, Vittorio; Adesso, Gerardo

2017-05-01

We consider an instance of "black-box" quantum metrology in the Gaussian framework, where we aim to estimate the amount of squeezing applied on an input probe, without previous knowledge on the phase of the applied squeezing. By taking the quantum Fisher information (QFI) as the figure of merit, we evaluate its average and variance with respect to this phase in order to identify probe states that yield good precision for many different squeezing directions. We first consider the case of single-mode Gaussian probes with the same energy, and find that pure squeezed states maximize the average quantum Fisher information (AvQFI) at the cost of a performance that oscillates strongly as the squeezing direction is changed. Although the variance can be brought to zero by correlating the probing system with a reference mode, the maximum AvQFI cannot be increased in the same way. A different scenario opens if one takes into account the effects of photon losses: coherent states represent the optimal single-mode choice when losses exceed a certain threshold and, moreover, correlated probes can now yield larger AvQFI values than all single-mode states, on top of having zero variance.

Intrinsic Fluorescence as a Spectral Probe for Protein Denaturation Studies in the Presence of Honey

NASA Astrophysics Data System (ADS)

Wong, Y. H.; Kadir, H. A.; Tayyab, S.

2015-11-01

Honey was found to quench the intrinsic fluorescence of bovine serum albumin (BSA) in a concentration dependent manner, showing complete quenching in the presence of 5% (w/v) honey. Increasing the protein concentration up to 5.0 μM did not lead to the recovery of the protein fluorescence. Urea denaturation of BSA, which otherwise shows a two-step, three-state transition, using intrinsic fluorescence of the protein as the probe failed to produce any result in the presence of 5% (w/v) honey. Thus, intrinsic fluorescence cannot be used as a spectral probe for protein denaturation studies in the presence of honey.

Dynamic current susceptibility as a probe of Majorana bound states in nanowire-based Josephson junctions

NASA Astrophysics Data System (ADS)

Trif, Mircea; Dmytruk, Olesia; Bouchiat, Hélène; Aguado, Ramón; Simon, Pascal

2018-02-01

We theoretically study a Josephson junction based on a semiconducting nanowire subject to a time-dependent flux bias. We establish a general density-matrix approach for the dynamical response of the Majorana junction and calculate the resulting flux-dependent susceptibility using both microscopic and effective low-energy descriptions for the nanowire. We find that the diagonal component of the susceptibility, associated with the dynamics of the Majorana state populations, dominates over the standard Kubo contribution for a wide range of experimentally relevant parameters. The diagonal term, explored, in this Rapid Communication, in the context of Majorana physics, allows probing accurately the presence of Majorana bound states in the junction.

Deep inelastic scattering as a probe of entanglement

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kharzeev, Dmitri E.; Levin, Eugene M.

Using nonlinear evolution equations of QCD, we compute the von Neumann entropy of the system of partons resolved by deep inelastic scattering at a given Bjorken x and momentum transfer q 2 = - Q 2 . We interpret the result as the entropy of entanglement between the spatial region probed by deep inelastic scattering and the rest of the proton. At small x the relation between the entanglement entropy S ( x ) and the parton distribution x G ( x ) becomes very simple: S ( x ) = ln [ x G ( x ) ] .more » In this small x , large rapidity Y regime, all partonic microstates have equal probabilities—the proton is composed by an exponentially large number exp ( Δ Y ) of microstates that occur with equal and exponentially small probabilities exp ( - Δ Y ) , where Δ is defined by x G ( x ) ~ 1 / x Δ . For this equipartitioned state, the entanglement entropy is maximal—so at small x , deep inelastic scattering probes a maximally entangled state. Here, we propose the entanglement entropy as an observable that can be studied in deep inelastic scattering. This will then require event-by-event measurements of hadronic final states, and would allow to study the transformation of entanglement entropy into the Boltzmann one. We estimate that the proton is represented by the maximally entangled state at x ≤ 10 -3 ; this kinematic region will be amenable to studies at the Electron Ion Collider.« less

Deep inelastic scattering as a probe of entanglement

DOE PAGES

Kharzeev, Dmitri E.; Levin, Eugene M.

2017-06-03

Using nonlinear evolution equations of QCD, we compute the von Neumann entropy of the system of partons resolved by deep inelastic scattering at a given Bjorken x and momentum transfer q 2 = - Q 2 . We interpret the result as the entropy of entanglement between the spatial region probed by deep inelastic scattering and the rest of the proton. At small x the relation between the entanglement entropy S ( x ) and the parton distribution x G ( x ) becomes very simple: S ( x ) = ln [ x G ( x ) ] .more » In this small x , large rapidity Y regime, all partonic microstates have equal probabilities—the proton is composed by an exponentially large number exp ( Δ Y ) of microstates that occur with equal and exponentially small probabilities exp ( - Δ Y ) , where Δ is defined by x G ( x ) ~ 1 / x Δ . For this equipartitioned state, the entanglement entropy is maximal—so at small x , deep inelastic scattering probes a maximally entangled state. Here, we propose the entanglement entropy as an observable that can be studied in deep inelastic scattering. This will then require event-by-event measurements of hadronic final states, and would allow to study the transformation of entanglement entropy into the Boltzmann one. We estimate that the proton is represented by the maximally entangled state at x ≤ 10 -3 ; this kinematic region will be amenable to studies at the Electron Ion Collider.« less

Surface and interface effects on non-radiative exciton recombination and relaxation dynamics in CdSe/Cd,Zn,S nanocrystals

NASA Astrophysics Data System (ADS)

Walsh, Brenna R.; Saari, Jonathan I.; Krause, Michael M.; Nick, Robert; Coe-Sullivan, Seth; Kambhampati, Patanjali

2016-06-01

Excitonic state-resolved pump/probe spectroscopy and time correlate single photon counting were used to study exciton dynamics from the femtosecond to nanosecond time scales in CdSe/Cd,Zn,S nanocrystals. These measurements reveal the role of the core/shell interface as well as surface on non-radiative excitonic processes over three time regimes. Time resolved photoluminescence reports on how the interface controls slow non-radiative processes that dictate emission at the single excitonic level. Heterogeneity in decay is minimized by interfacial structure. Pump/probe measurements explore the non-radiative multiexcitonic recombination processes on the picosecond timescale. These Auger based non-radiative processes dictate lifetimes of multiexcitonic states. Finally state-resolved pump/probe measurements on the femtosecond timescale reveal the influence of the interface on electron and hole relaxation dynamics. We find that the interface has a profound influence on all three types of non-radiative processes which ultimately control light emission from nanocrystals.

Distance Probes of Dark Energy

DOE PAGES

Kim, A. G.; Padmanabhan, N.; Aldering, G.; ...

2015-03-15

We present the results from the Distances subgroup of the Cosmic Frontier Community Planning Study (Snowmass 2013). This document summarizes the current state of the field as well as future prospects and challenges. In addition to the established probes using Type Ia supernovae and baryon acoustic oscillations, we also consider prospective methods based on clusters, active galactic nuclei, gravitational wave sirens and strong lensing time delays.

Technique for temperature compensation of eddy-current proximity probes

NASA Technical Reports Server (NTRS)

Masters, Robert M.

1989-01-01

Eddy-current proximity probes are used in turbomachinery evaluation testing and operation to measure distances, primarily vibration, deflection, or displacment of shafts, bearings and seals. Measurements of steady-state conditions made with standard eddy-current proximity probes are susceptible to error caused by temperature variations during normal operation of the component under investigation. Errors resulting from temperature effects for the specific probes used in this study were approximately 1.016 x 10 to the -3 mm/deg C over the temperature range of -252 to 100 C. This report examines temperature caused changes on the eddy-current proximity probe measurement system, establishes their origin, and discusses what may be done to minimize their effect on the output signal. In addition, recommendations are made for the installation and operation of the electronic components associated with an eddy-current proximity probe. Several techniques are described that provide active on-line error compensation for over 95 percent of the temperature effects.

A versatile and reconfigurable setup for all-terahertz time-resolved pump-probe spectroscopy.

PubMed

Elezzabi, A Y; Maraghechi, P

2012-05-01

A versatile optical setup for all-terahertz (THz) time resolved pump-probe spectroscopy was designed and tested. By utilizing a dual THz pulse generator emitter module, independent and synchronized THz radiation pump and probe pulses were produced, thus eliminating the need for THz beam splitters and the limitations associated with their implementation. The current THz setup allows for precise control of the electric fields splitting ratio between the THz radiation pump and probe pulses, as well as in-phase, out-of-phase, and polarization dependent pump-probe spectroscopy. Since the present THz pump-probe setup does not require specialized THz radiation optical components, such as phase shifters, polarization rotators, or wide bandwidth beam splitters, it can be easily implemented with minimal alterations to a conventional THz time domain spectroscopy system. The present setup is valuable for studying the time dynamics of THz coherent phenomena in solid-state, chemical, and biological systems.

Probing excitons in transition metal dichalcogenides by Drude-like exciton intraband absorption.

PubMed

Zhao, Siqi; He, Dawei; He, Jiaqi; Zhang, Xinwu; Yi, Lixin; Wang, Yongsheng; Zhao, Hui

2018-05-24

Understanding excitonic dynamics in two-dimensional semiconducting transition metal dichalcogenides is important for developing their optoelectronic applications. Recently, transient absorption techniques based on resonant excitonic absorption have been used to study various aspects of excitonic dynamics in these materials. The transient absorption in such measurements originates from phase-space state filling, bandgap renormalization, or screening effects. Here we report a new method to probe excitonic dynamics based on exciton intraband absorption. In this Drude-like process, probe photons are absorbed by excitons in their intraband excitation to higher energy states, causing a transient absorption signal. Although the magnitude of the transient absorption is lower than that of the resonant techniques, the new method is less restrictive on the selection of probe wavelength, has a larger linear range, and can provide complementary information on photocarrier dynamics. Using the WS2 monolayer and bulk samples as examples, we show that the new method can probe exciton-exciton annihilation at high densities and reveal exciton formation processes. We also found that the exciton intraband absorption cross section of the WS2 monolayer is on the order of 10-18 cm2.

Reactive ground-state pathways are not ubiquitous in red/green cyanobacteriochromes.

PubMed

Chang, Che-Wei; Gottlieb, Sean M; Kim, Peter W; Rockwell, Nathan C; Lagarias, J Clark; Larsen, Delmar S

2013-09-26

Recent characterization of the red/green cyanobacteriochrome (CBCR) NpR6012g4 revealed a high quantum yield for its forward photoreaction [J. Am. Chem. Soc. 2012, 134, 130-133] that was ascribed to the activity of hidden, productive ground-state intermediates. The dynamics of the pathways involving these ground-state intermediates was resolved with femtosecond dispersed pump-dump-probe spectroscopy, the first such study reported for any CBCR. To address the ubiquity of such second-chance initiation dynamics (SCID) in CBCRs, we examined the closely related red/green CBCR NpF2164g6 from Nostoc punctiforme. Both NpF2164g6 and NpR6012g4 use phycocyanobilin as the chromophore precursor and exhibit similar excited-state dynamics. However, NpF2164g6 exhibits a lower quantum yield of 32% for the generation of the isomerized Lumi-R primary photoproduct, compared to 40% for NpR6012g4. This difference arises from significantly different ground-state dynamics between the two proteins, with the SCID mechanism deactivated in NpF2164g6. We present an integrated inhomogeneous target model that self-consistently fits the pump-probe and pump-dump-probe signals for both forward and reverse photoreactions in both proteins. This work demonstrates that reactive ground-state intermediates are not ubiquitous phenomena in CBCRs.

Quantum control and measurement of atomic spins in polarization spectroscopy

NASA Astrophysics Data System (ADS)

Deutsch, Ivan H.; Jessen, Poul S.

2010-03-01

Quantum control and measurement are two sides of the same coin. To affect a dynamical map, well-designed time-dependent control fields must be applied to the system of interest. To read out the quantum state, information about the system must be transferred to a probe field. We study a particular example of this dual action in the context of quantum control and measurement of atomic spins through the light-shift interaction with an off-resonant optical probe. By introducing an irreducible tensor decomposition, we identify the coupling of the Stokes vector of the light field with moments of the atomic spin state. This shows how polarization spectroscopy can be used for continuous weak measurement of atomic observables that evolve as a function of time. Simultaneously, the state-dependent light shift induced by the probe field can drive nonlinear dynamics of the spin, and can be used to generate arbitrary unitary transformations on the atoms. We revisit the derivation of the master equation in order to give a unified description of spin dynamics in the presence of both nonlinear dynamics and photon scattering. Based on this formalism, we review applications to quantum control, including the design of state-to-state mappings, and quantum-state reconstruction via continuous weak measurement on a dynamically controlled ensemble.

Effect of number of probes and their orientation on the calculation of several compressor face distortion descriptors

NASA Technical Reports Server (NTRS)

Stoll, F.; Tremback, J. W.; Arnaiz, H. H.

1979-01-01

A study was performed to determine the effects of the number and position of total pressure probes on the calculation of five compressor face distortion descriptors. This study used three sets of 320 steady state total pressure measurements that were obtained with a special rotating rake apparatus in wind tunnel tests of a mixed-compression inlet. The inlet was a one third scale model of the inlet on a YF-12 airplane, and it was tested in the wind tunnel at representative flight conditions at Mach numbers above 2.0. The study shows that large errors resulted in the calculation of the distortion descriptors even with a number of probes that were considered adequate in the past. There were errors as large as 30 and -50 percent in several distortion descriptors for a configuration consisting of eight rakes with five equal-area-weighted probes on each rake.

[Caries and periodontal state of pregnant women. Part II. Periodontal state].

PubMed

Radnai, Márta; Gorzó, István; Nagy, Erzsébet; Urbán, Edit; Eller, József; Novák, Tibor; Pál, Attila

2005-06-01

A great number of clinical studies focused on the periodontal health of the pregnant women in the last decades, since an association has been presumed between the pregnant women's periodontal disease and the adverse pregnancy outcome. Altogether 161 healthy women were examined soon after delivery in Szeged/Hungary. The periodontal status of the patients was recorded by the Silness-Löe Plaque index (0.67), frequency of calculus (21.07%), mean probing pocket depth (1.67 mm) and the frequency of bleeding on probing (37.8%). A significant correlation was found between the state of the periodontium and the educational level and the pregnant women's profession. The periodontal state of women with higher education and the intellectuals was much better, than of the less educated patients and the manual workers.

Ultrafast photodissociation dynamics of 1,4-diiodobenzene

NASA Astrophysics Data System (ADS)

Stankus, Brian; Zotev, Nikola; Rogers, David M.; Gao, Yan; Odate, Asami; Kirrander, Adam; Weber, Peter M.

2018-05-01

The photodissociation dynamics of 1,4-diiodobenzene is investigated using ultrafast time-resolved photoelectron spectroscopy. Following excitation by laser pulses at 271 nm, the excited-state dynamics is probed by resonance-enhanced multiphoton ionization with 405 nm probe pulses. A progression of Rydberg states, which come into resonance sequentially, provide a fingerprint of the dissociation dynamics of the molecule. The initial excitation decays with a lifetime of 33 ± 4 fs, in good agreement with a previous study. The spectrum is interpreted by reference to ab initio calculations at the CASPT2(18,14) level, including spin-orbit coupling. We propose that both the 5B1 and 6B1 states are excited initially, and based on the calculations, we identify diabatic spin-orbit coupled states corresponding to the main dissociation pathways.

Development of a Methodology for the Characterisation of Air-coupled Ultrasound Probes

NASA Astrophysics Data System (ADS)

Pietroni, Paolo; Marco Revel, Gian

2010-05-01

This study is aimed at developing a technique for the characterisation of air-coupled ultrasound probes, starting from the analysis of the mechanical behaviour of the probe membrane. The vibratory behaviour of the emission membrane is studied using laser-Doppler vibrometry techniques with high frequency demodulation system (20 MHz). The determination of the vibration provides information which are useful for the assessment of the performance of the probe, in particular concerning the Quality factor and the portion of the membrane which really contributes to the emission. During the second step the results of the vibration measurements are used to calculate, by means of numerical boundary element method, the ultrasound beam emitted in terms of intensity in space. The obtained field is compared with the direct measurements carried out by scanning with the receiver probe and a pinhole plate. This comparison allows the potential and the problems of the two different characterisation techniques to be determined, even if the pinhole technique (which is currently considered the state of the art) cannot be used as an absolute reference. This study appears to be useful for paving the way for a new methodology for the calibration of air-coupled ultrasound probes, which potentially could be used not only to improve the probe manufacturing process, but also to control conformity to specifications.

Mechanism of the reaction, CH4+O(1D2)→CH3+OH, studied by ultrafast and state-resolved photolysis/probe spectroscopy of the CH4ṡO3 van der Waals complex

NASA Astrophysics Data System (ADS)

Miller, C. Cameron; van Zee, Roger D.; Stephenson, John C.

2001-01-01

The mechanism of the reaction CH4+O(1D2)→CH3+OH was investigated by ultrafast, time-resolved and state-resolved experiments. In the ultrafast experiments, short ultraviolet pulses photolyzed ozone in the CH4ṡO3 van der Waals complex to produce O(1D2). The ensuing reaction with CH4 was monitored by measuring the appearance rate of OH(v=0,1;J,Ω,Λ) by laser-induced fluorescence, through the OH A←X transition, using short probe pulses. These spectrally broad pulses, centered between 307 and 316 nm, probe many different OH rovibrational states simultaneously. At each probe wavelength, both a fast and a slow rise time were evident in the fluorescence signal, and the ratio of the fast-to-slow signal varied with probe wavelength. The distribution of OH(v,J,Ω,Λ) states, Pobs(v,J,Ω,Λ), was determined by laser-induced fluorescence using a high-resolution, tunable dye laser. The Pobs(v,J,Ω,Λ) data and the time-resolved data were analyzed under the assumption that different formation times represent different reaction mechanisms and that each mechanism produces a characteristic rovibrational distribution. The state-resolved and the time-resolved data can be fit independently using a two-mechanism model: Pobs(v,J,Ω,Λ) can be decomposed into two components, and the appearance of OH can be fit by two exponential rise times. However, these independent analyses are not mutually consistent. The time-resolved and state-resolved data can be consistently fit using a three-mechanism model. The OH appearance signals, at all probe wavelengths, were fit with times τfast≈0.2 ps, τinter≈0.5 ps and τslow≈5.4 ps. The slowest of these three is the rate for dissociation of a vibrationally excited methanol intermediate (CH3OH*) predicted by statistical theory after complete intramolecular energy redistribution following insertion of O(1D2) into CH4. The Pobs(v,J,Ω,Λ) was decomposed into three components, each with a linear surprisal, under the assumption that the mechanism producing OH at a statistical rate would be characterized by a statistical prior. Dissociation of a CH4O* intermediate before complete energy randomization was identified as producing OH at the intermediate rate and was associated with a population distribution with more rovibrational energy than the slow mechanism. The third mechanism produces OH promptly with a cold rovibrational distribution, indicative of a collinear abstraction mechanism. After these identifications were made, it was possible to predict the fraction of signal associated with each mechanism at different probe wavelengths in the ultrafast experiment, and the predictions proved consistent with measured appearance signals. This model also reconciles data from a variety of previous experiments. While this model is the simplest that is consistent with the data, it is not definitive for several reasons. First, the appearance signals measured in these experiments probe simultaneously many OH(v,J,Ω,Λ) states, which would tend to obfuscate differences in the appearance rate of specific rovibrational states. Second, only about half of the OH(v,J,Ω,Λ) states populated by this reaction could be probed by laser-induced fluorescence through the OH A←X band with our apparatus. Third, the cluster environment might influence the dynamics compared to the free bimolecular reaction.

Pump-probe optical microscopy for imaging nonfluorescent chromophores.

PubMed

Wei, Lu; Min, Wei

2012-06-01

Many chromophores absorb light intensely but have undetectable fluorescence. Hence microscopy techniques other than fluorescence are highly desirable for imaging these chromophores inside live cells, tissues, and organisms. The recently developed pump-probe optical microscopy techniques provide fluorescence-free contrast mechanisms by employing several fundamental light-molecule interactions including excited state absorption, stimulated emission, ground state depletion, and the photothermal effect. By using the pump pulse to excite molecules and the subsequent probe pulse to interrogate the created transient states on a laser scanning microscope, pump-probe microscopy offers imaging capability with high sensitivity and specificity toward nonfluorescent chromophores. Single-molecule sensitivity has even been demonstrated. Here we review and summarize the underlying principles of this emerging class of molecular imaging techniques.

Estimation of ion charge states using Van Allen Probes-RBSPICE: a case study

NASA Astrophysics Data System (ADS)

Farinas Perez, G.; Sibeck, D. G.

2017-12-01

We use data from the RBSPICE instrument aboard the Van Allen Probes spacecraft to identify particle injection events with ion drift echoes. We calculate the arrival time and drift period of the protons, helium and oxygen for every energy channel of the RBSPICE instrument. The ions drift period depends upon their energy and charge, as we know the particle energy and the time drift period, the charge state can be estimated for a dipolar magnetic field model. A drift-echo event occurred in May 23, 2013 at 0400 UT is analyzed.

Probing semiconductor gap states with resonant tunneling.

PubMed

Loth, S; Wenderoth, M; Winking, L; Ulbrich, R G; Malzer, S; Döhler, G H

2006-02-17

Tunneling transport through the depletion layer under a GaAs {110} surface is studied with a low temperature scanning tunneling microscope (STM). The observed negative differential conductivity is due to a resonant enhancement of the tunneling probability through the depletion layer mediated by individual shallow acceptors. The STM experiment probes, for appropriate bias voltages, evanescent states in the GaAs band gap. Energetically and spatially resolved spectra show that the pronounced anisotropic contrast pattern of shallow acceptors occurs exclusively for this specific transport channel. Our findings suggest that the complex band structure causes the observed anisotropies connected with the zinc blende symmetry.

Probing the density of trap states in the middle of the bandgap using ambipolar organic field-effect transistors

NASA Astrophysics Data System (ADS)

Häusermann, Roger; Chauvin, Sophie; Facchetti, Antonio; Chen, Zhihua; Takeya, Jun; Batlogg, Bertram

2018-04-01

The number of trap states in the band gap of organic semiconductors directly influences the charge transport as well as the threshold and turn-on voltage. Direct charge transport measurements have been used until now to probe the trap states rather close to the transport level, whereas their number in the middle of the band gap has been elusive. In this study, we use PDIF-CN2, a well known n-type semiconductor, together with vanadium pentoxide electrodes to build ambipolar field-effect transistors. Employing three different methods, we study the density of trap states in the band gap of the semiconductor. These methods give consistent results, and no pool of defect states was found. Additionally, we show first evidence that the number of trap states close to the transport level is correlated with the number of traps in the middle of the band-gap, meaning that a high number of trap states close to the transport level also implies a high number of trap states in the middle of the band gap. This points to a common origin of the trap states over a wide energy range.

Pump and probe spectroscopy with continuous wave quantum cascade lasers.

PubMed

Kirkbride, James M R; Causier, Sarah K; Dalton, Andrew R; Weidmann, Damien; Ritchie, Grant A D

2014-02-07

This paper details infra-red pump and probe studies on nitric oxide conducted with two continuous wave quantum cascade lasers both operating around 5 μm. The pump laser prepares a velocity selected population in a chosen rotational quantum state of the v = 1 level which is subsequently probed using a second laser tuned to a rotational transition within the v = 2 ← v = 1 hot band. The rapid frequency scan of the probe (with respect to the molecular collision rate) in combination with the velocity selective pumping allows observation of marked rapid passage signatures in the transient absorption profiles from the polarized vibrationally excited sample. These coherent transient signals are influenced by the underlying hyperfine structure of the pump and probe transitions, the sample pressure, and the coherent properties of the lasers. Pulsed pump and probe studies show that the transient absorption signals decay within 1 μs at 50 mTorr total pressure, reflecting both the polarization and population dephasing times of the vibrationally excited sample. The experimental observations are supported by simulation based upon solving the optical Bloch equations for a two level system.

Scanning Probe Microscopies and Their Applications Towards the Study of Superconductors

NASA Astrophysics Data System (ADS)

Helfrich, Jennifer Ann

1995-11-01

The invention of the scanning tunneling microscope (STM) in 1982 made it possible to study surfaces and structures at resolutions previously believed unattainable. Adapting the STM for low temperatures makes it possible to study superconductors with new methods and to obtain valuable information. This thesis describes a novel low temperature STM (LTSTM) that was designed and built at Northwestern University for the purpose of studying superconductors in the mixed state. At low temperatures, this LTSTM has a scan range an order of magnitude larger than other LTSTM's designed elsewhere. It is capable of low temperature imaging and obtaining dI/dV vs. V curves. A detailed study of magnetic force microscopy (MFM) probes is also presented. The fields and forces between probe and surface were computer modeled. These results are compared with results from electron holographs of MFM probes. The final section of the thesis describes an a.c. susceptibility measurement on a UPt_3 sphere. Results are presented and discussed.

Pump-probe spectroscopy in organic semiconductors: monitoring fundamental processes of relevance in optoelectronics.

PubMed

Cabanillas-Gonzalez, Juan; Grancini, Giulia; Lanzani, Guglielmo

2011-12-08

In this review we highlight the contribution of pump-probe spectroscopy to understand elementary processes taking place in organic based optoelectronic devices. The techniques described in this article span from conventional pump-probe spectroscopy to electromodulated pump-probe and the state-of-the-art confocal pump-probe microscopy. The article is structured according to three fundamental processes (optical gain, charge photogeneration and charge transport) and the contribution of these techniques on them. The combination of these tools opens up new perspectives for assessing the role of short-lived excited states on processes lying underneath organic device operation. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Low power ovonic threshold switching characteristics of thin GeTe{sub 6} films using conductive atomic force microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Manivannan, Anbarasu, E-mail: anbarasu@iiti.ac.in, E-mail: ranjith@iith.ac.in; Sahu, Smriti; Myana, Santosh Kumar

2014-12-15

Minimizing the dimensions of the electrode could directly impact the energy-efficient threshold switching and programming characteristics of phase change memory devices. A ∼12–15 nm AFM probe-tip was employed as one of the electrodes for a systematic study of threshold switching of as-deposited amorphous GeTe{sub 6} thin films. This configuration enables low power threshold switching with an extremely low steady state current in the on state of 6–8 nA. Analysis of over 48 different probe locations on the sample reveals a stable Ovonic threshold switching behavior at threshold voltage, V{sub TH} of 2.4 ± 0.5 V and the off state was retained below a holding voltage,more » V{sub H} of 0.6 ± 0.1 V. All these probe locations exhibit repeatable on-off transitions for more than 175 pulses at each location. Furthermore, by utilizing longer biasing voltages while scanning, a plausible nano-scale control over the phase change behavior from as-deposited amorphous to crystalline phase was studied.« less

Coherence specific signal detection via chiral pump-probe spectroscopy.

PubMed

Holdaway, David I H; Collini, Elisabetta; Olaya-Castro, Alexandra

2016-05-21

We examine transient circular dichroism (TRCD) spectroscopy as a technique to investigate signatures of exciton coherence dynamics under the influence of structured vibrational environments. We consider a pump-probe configuration with a linearly polarized pump and a circularly polarized probe, with a variable angle θ between the two directions of propagation. In our theoretical formalism the signal is decomposed in chiral and achiral doorway and window functions. Using this formalism, we show that the chiral doorway component, which beats during the population time, can be isolated by comparing signals with different values of θ. As in the majority of time-resolved pump-probe spectroscopy, the overall TRCD response shows signatures of both excited and ground state dynamics. However, we demonstrate that the chiral doorway function has only a weak ground state contribution, which can generally be neglected if an impulsive pump pulse is used. These findings suggest that the pump-probe configuration of optical TRCD in the impulsive limit has the potential to unambiguously probe quantum coherence beating in the excited state. We present numerical results for theoretical signals in an example dimer system.

Interference of flavonoids with fluorescent intracellular probes: methodological implications in the evaluation of the oxidative burst by flow cytometry.

PubMed

Peluso, Ilaria; Manafikhi, Husseen; Reggi, Raffaella; Palmery, Maura

2014-08-01

The evaluation of oxidative burst is particularly relevant in many pathological and subclinical conditions. Flow cytometry provides quick and accurate measures of the reactive oxygen species production by leukocytes in most situations. However, spurious results, related to probes' efflux may be observed in several instances. Many factors affect the evaluation of the oxidative burst with fluorescent probes that require intracellular deacetylation and could be substrate of the multidrug resistance proteins (MDR). After discussing the implications of the efflux of fluorophores in the normalization strategies in flow cytometry assays, we have pointed out the possible interference of flavonoids with fluorescet probes' staining and signal. We have also reviewed the results from human intervention studies regarding the evaluation of oxidative burst with these probes. In vitro, at concentrations close to post-ingestion circulating levels, some flavonoids and their metabolites could interfere with probes' staining and fluorescence signal through different mechanisms, such as the inhibition of esterases, the modulation of the MDR-mediate efflux of probe and the inhibition of the oxidation of probe. These effects may explain the contrasting results obtained by human intervention studies. Finally, also inflammatory state or the use of drugs substrate of MDR proteins could affect the evaluation of the oxidative burst with intracellular probes. © 2014 International Society for Advancement of Cytometry.

Nonradiative relaxation in tunable solid state laser crystals

NASA Technical Reports Server (NTRS)

Gayen, S. K.; Wang, W. B.; Petricevic, V.; Alfano, R. R.

1986-01-01

The characteristics of nonradiative transitions between the 4T2 and 2E excited states of trivalent-chromium-ion-activated ruby (containing 0.04 percent Cr2O3 by weight) and alexandrite (containing 0.4 at. percent chromium ion) laser crystals were studied using the technique described by Gayen et al. (1985). In this technique, a 527-nm pulse excites the 4T2 band of the Cr(3+), and the subsequent population kinetics among excited states is monitored by an IR picosecond probe pulse as a function of pump-probe delay. In ruby, a resolution-limited sharp rise in the excited state population was followed by a long-lifetime decay, leading to an upper limit of 7 ps for the 4T2-state nonradiative lifetime. In alexandrite, a longer rise time was followed by a multicomponent decay. A theoretical model is proposed for explaining the induced absorption and the transition dynamics observed in these crystals.

An Experimental Evaluation of the Performance of Two Combination Pitot Pressure Probes

NASA Technical Reports Server (NTRS)

Arend, David J.; Saunders, John D.

2009-01-01

Experimental tests have been completed which recorded the ability of two combination steady state and high response time varying Pitot probe designs to accurately measure steady stagnation pressure at a single location in a flow field. Tests were conducted of double-barreled and coannular Prati probes in a 3.5 in. diameter free jet probe calibration facility from Mach 0.1 to 0.9. Geometric symmetry and pitch (-40 deg to 40 deg) and yaw (0 deg to 40 deg) angle actuation were used to fully evaluate the probes. These tests revealed that the double-barreled configuration induced error in its steady state measurement at zero incidence that increased consistently with jet Mach number to 1.1 percent at Mach 0.9. For all Mach numbers, the double-barreled probe nulled at a pitch angle of approximately 7.0 deg and provided inconsistent measurements when yawed. The double-barreled probe provided adequate measurements via both its steady state and high response tubes (within +/- 0.15 percent accuracy) over unacceptable ranges of biased pitch and inconsistent yaw angles which varied with Mach number. By comparison, the coannular probe provided accurate measurements (at zero incidence) for all jet Mach numbers as well as over a flow angularity range which varied from +/- 26.0 deg at Mach 0.3 deg to +/- 14.0 deg at Mach 0.9. Based on these results, the Prati probe is established as the preferred design. Further experimental tests are recommended to document the frequency response characteristics of the Prati probe.

Efficient design of multituned transmission line NMR probes: the electrical engineering approach.

PubMed

Frydel, J A; Krzystyniak, M; Pienkowski, D; Pietrzak, M; de Sousa Amadeu, N; Ratajczyk, T; Idzik, K; Gutmann, T; Tietze, D; Voigt, S; Fenn, A; Limbach, H H; Buntkowsky, G

2011-01-01

Transmission line-based multi-channel solid state NMR probes have many advantages regarding the cost of construction, number of RF-channels, and achievable RF-power levels. Nevertheless, these probes are only rarely employed in solid state-NMR-labs, mainly owing to the difficult experimental determination of the necessary RF-parameters. Here, the efficient design of multi-channel solid state MAS-NMR probes employing transmission line theory and modern techniques of electrical engineering is presented. As technical realization a five-channel ((1)H, (31)P, (13)C, (2)H and (15)N) probe for operation at 7 Tesla is described. This very cost efficient design goal is a multi port single coil transmission line probe based on the design developed by Schaefer and McKay. The electrical performance of the probe is determined by measuring of Scattering matrix parameters (S-parameters) in particular input/output ports. These parameters are compared to the calculated parameters of the design employing the S-matrix formalism. It is shown that the S-matrix formalism provides an excellent tool for examination of transmission line probes and thus the tool for a rational design of these probes. On the other hand, the resulting design provides excellent electrical performance. From a point of view of Nuclear Magnetic Resonance (NMR), calibration spectra of particular ports (channels) are of great importance. The estimation of the π/2 pulses length for all five NMR channels is presented. Copyright © 2011 Elsevier Inc. All rights reserved.

Characterization of the intramolecular transfer state of marine carotenoid fucoxanthin by femtosecond pump-probe spectroscopy.

PubMed

Kosumi, Daisuke; Fujii, Ritsuko; Sugisaki, Mitsuru; Oka, Naohiro; Iha, Masahiko; Hashimoto, Hideki

2014-07-01

Fucoxanthin, containing a carbonyl group in conjugation with its polyene backbone, is a naturally occurring pigment in marine organisms and is essential to the photosynthetic light-harvesting function in brown alga and diatom. Fucoxanthin exhibits optical characteristics attributed to an intramolecular charge transfer (ICT) state that arises in polar environments due to the presence of the carbonyl group. In this study, we report the spectroscopic properties of fucoxanthin in methanol (polar and protic solvent) observed by femtosecond pump-probe measurements in the near-infrared region, where transient absorption associated with the optically allowed S2 (1(1)B u (+) ) state and stimulated emission from the strongly coupled S1/ICT state were observed following one-photon excitation to the S2 state. The results showed that the amplitude of the stimulated emission of the S1/ICT state increased with decreasing excitation energy, demonstrating that the fucoxanthin form associated with the lower energy of the steady-state absorption exhibits stronger ICT character.

Fluorescent molecular probes based on excited state prototropism in lipid bilayer membrane

NASA Astrophysics Data System (ADS)

Mohapatra, Monalisa; Mishra, Ashok K.

2012-03-01

Excited state prototropism (ESPT) is observed in molecules having one or more ionizable protons, whose proton transfer efficiency is different in ground and excited states. The interaction of various ESPT molecules like naphthols and intramolecular ESPT (ESIPT) molecules like hydroxyflavones etc. with different microheterogeneous media have been studied in detail and excited state prototropism as a probe concept has been gaining ground. The fluorescence of different prototropic forms of such molecules, on partitioning to an organized medium like lipid bilayer membrane, often show sensitive response to the local environment with respect to the local structure, physical properties and dynamics. Our recent work using 1-naphthol as an ESPT fluorescent molecular probe has shown that the incorporation of monomeric bile salt molecules into lipid bilayer membranes composed from dipalmitoylphosphatidylcholine (DPPC, a lung surfactant) and dimyristoylphosphatidylcholine (DMPC), in solid gel and liquid crystalline phases, induce appreciable wetting of the bilayer up to the hydrocarbon core region, even at very low (<= 1 mM) concentrations of the bile salts. The incorporation and location of fisetin, an ESIPT molecule having antioxidant properties, in lipid bilayer membrane has been sensitively monitored from its intrinsic fluorescence behaviour.

Analysis of all-optical light modulation in proteorhodopsin protein molecules

NASA Astrophysics Data System (ADS)

Roy, Sukhdev; Sharma, Parag

2008-03-01

We present a detailed steady-state and time-dependent theoretical analysis of all-optical light modulation in the recently discovered, wild-type proteorhodopsin (WTpR) protein molecules based on excited-state absorption. Amplitude modulation of cw probe laser beam transmissions at 520, 405, 555 and 560 nm, corresponding to the peak absorption of pR, pRM, pRK and pRN intermediate states of pR photocycle, respectively, by cw and pulsed modulating pump laser beam at 520 nm have been analyzed. The effect of various spectral and kinetic parameters on modulation characteristics has been studied. There is an optimum value of concentration for a given pump intensity value for which maximum modulation of the probe beam can be achieved. The switching characteristics of probe beam at 405 and 520 nm exhibit dip and peak, respectively, which can be removed by decreasing the absorption of pRM state at 520 nm. The modulation in WTpR is at lower pump powers with smaller contrast in comparison to WT bacteriorhodopsin (bR) and WT pharaonis phoborhodopsin (ppR). The modulation characteristics exhibit unique features compared to bR and ppR.

Microencapsulated fluorescent pH probe as implantable sensor for monitoring the physiological state of fish embryos.

PubMed

Gurkov, Anton; Sadovoy, Anton; Shchapova, Ekaterina; Teh, Cathleen; Meglinski, Igor; Timofeyev, Maxim

2017-01-01

In vivo physiological measurement is a major challenge in modern science and technology, as is environment conservation at the global scale. Proper toxicological testing of widely produced mixtures of chemicals is a necessary step in the development of new products, allowing us to minimize the human impact on aquatic ecosystems. However, currently available bioassay-based techniques utilizing small aquatic organisms such as fish embryos for toxicity testing do not allow assessing in time the changes in physiological parameters in the same individual. In this study, we introduce microencapsulated fluorescent probes as a promising tool for in vivo monitoring of internal pH variation in zebrafish embryos. The pH alteration identified under stress conditions demonstrates the applicability of the microencapsulated fluorescent probes for the repeated analysis of the embryo's physiological state. The proposed approach has strong potential to simultaneously measure a range of physiological characteristics using a set of specific fluorescent probes and to finally bring toxicological bioassays and related research fields to a new level of effectiveness and sensitivity.

Vibrational energy flow in photoactive yellow protein revealed by infrared pump-visible probe spectroscopy.

PubMed

Nakamura, Ryosuke; Hamada, Norio

2015-05-14

Vibrational energy flow in the electronic ground state of photoactive yellow protein (PYP) is studied by ultrafast infrared (IR) pump-visible probe spectroscopy. Vibrational modes of the chromophore and the surrounding protein are excited with a femtosecond IR pump pulse, and the subsequent vibrational dynamics in the chromophore are selectively probed with a visible probe pulse through changes in the absorption spectrum of the chromophore. We thus obtain the vibrational energy flow with four characteristic time constants. The vibrational excitation with an IR pulse at 1340, 1420, 1500, or 1670 cm(-1) results in ultrafast intramolecular vibrational redistribution (IVR) with a time constant of 0.2 ps. The vibrational modes excited through the IVR process relax to the initial ground state with a time constant of 6-8 ps in parallel with vibrational cooling with a time constant of 14 ps. In addition, upon excitation with an IR pulse at 1670 cm(-1), we observe the energy flow from the protein backbone to the chromophore that occurs with a time constant of 4.2 ps.

Optoelectronically probing the density of nanowire surface trap states to the single state limit

NASA Astrophysics Data System (ADS)

Dan, Yaping

2015-02-01

Surface trap states play a dominant role in the optoelectronic properties of nanoscale devices. Understanding the surface trap states allows us to properly engineer the device surfaces for better performance. But characterization of surface trap states at nanoscale has been a formidable challenge using the traditional capacitive techniques. Here, we demonstrate a simple but powerful optoelectronic method to probe the density of nanowire surface trap states to the single state limit. In this method, we choose to tune the quasi-Fermi level across the bandgap of a silicon nanowire photoconductor, allowing for capture and emission of photogenerated charge carriers by surface trap states. The experimental data show that the energy density of nanowire surface trap states is in a range from 109 cm-2/eV at deep levels to 1012 cm-2/eV near the conduction band edge. This optoelectronic method allows us to conveniently probe trap states of ultra-scaled nano/quantum devices at extremely high precision.

Charge dynamics of 57Fe probe atoms in La2Li0.5Cu0.5O4

NASA Astrophysics Data System (ADS)

Presniakov, I. A.; Sobolev, A. V.; Rusakov, V. S.; Moskvin, A. S.; Baranov, A. V.

2018-06-01

The objective of this study is to characterize the electronic state and local surrounding of 57Fe Mössbauer probe atoms within iron-doped layered perovskite La2Li0.5Cu0.5O4 containing transition metal in unusual formal oxidation states "+3". An approach based on the qualitative energy diagrams analysis and the calculations within the cluster configuration interaction method have been developed. It was shown that a large amount of charge is transferred via Cu-O bonds from the O: 2p bands to the Cu: 3d orbitals and the ground state is dominated by the d9L configuration ("Cu2+-O-" state). The dominant d9L ground state for the (CuO6) sublattice induces in the environment of the 57Fe probe cations a charge transfer Fe3+ + O-(L) → Fe4+ + O2-, which transforms "Fe3+" into "Fe4+" state. The experimental spectra in the entire temperature range 77-300 K were described with the use of the stochastic two-level model based on the assumption of dynamic equilibrium between two Fe3+↔Fe4+ valence states related to the iron atom in the [Fe(1)O4]4- center. The relaxation frequencies and activation energies of the corresponding charge fluctuations were estimated based on Mössbauer data. The results are discussed assuming a temperature-induced change in the electronic state of the [CuO4]5- clusters in the layered perovskite.

Blue Whale Behavioral Response Study & Field Testing of the New Bioacoustic Probe

DTIC Science & Technology

2009-09-30

New Bioacoustic Probe Erin M. Oleson NOAA-NMFS-Pacific Islands Fisheries Science Center 1601 Kapiolani Blvd. Ste. 1110, Honolulu, HI 96814...NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) NOAA-NMFS-Pacific Islands Fisheries Science Center,1601...goal is to bring the new tag into a field- ready state for community -wide use of the tag with a variety of cetacean species to study vocal and dive

Electronic and Vibrational Coherence in Charge-Transfer Reactions

NASA Astrophysics Data System (ADS)

Scherer, Norbert

1996-03-01

The ultrafast dynamics associated with optically-induced intervalence charge-transfer reactions in solution and protein environments are reported. These studies include the Fe^(II)-Fe^(III) MMCT complex Prussian blue and the mixed valence dimer (CN)_5Ru^(II)CNRuRu^(III)(NH_3)_5. The protein systems include blue copper proteins and the bacterial photosynthetic reaction center. The experimental approaches include photon echo, wavelength-resolved pump-probe and anisotropy measurements performed with 12-16fs duration optical pulses. Complicated time-domain waveforms reflect the several different p[rocesses and time scales for relaxation of coherences (both electronic and vibrational) and populations within these systems. The photon echo and anisotropy results probe electronic coherence and dephasing prior to back electron transfer. Wavelength-resolved pump-probe results reveal vibrational modes coupled to the CT-coordinate as well as formation of new product states or vibrational cooling in the ground state following back electron transfer.

Broad-Band Pump-Probe Spectroscopy Quantifies Ultrafast Solvation Dynamics of Proteins and Molecules.

PubMed

Jumper, Chanelle C; Arpin, Paul C; Turner, Daniel B; McClure, Scott D; Rafiq, Shahnawaz; Dean, Jacob C; Cina, Jeffrey A; Kovac, Philip A; Mirkovic, Tihana; Scholes, Gregory D

2016-11-17

In this work, we demonstrate the use of broad-band pump-probe spectroscopy to measure femtosecond solvation dynamics. We report studies of a rhodamine dye in methanol and cryptophyte algae light-harvesting proteins in aqueous suspension. Broad-band impulsive excitation generates a vibrational wavepacket that oscillates on the excited-state potential energy surface, destructively interfering with itself at the minimum of the surface. This destructive interference gives rise to a node at a certain probe wavelength that varies with time. This reveals the Gibbs free-energy changes of the excited-state potential energy surface, which equates to the solvation time correlation function. This method captures the inertial solvent response of water (∼40 fs) and the bimodal inertial response of methanol (∼40 and ∼150 fs) and reveals how protein-buried chromophores are sensitive to the solvent dynamics inside and outside of the protein environment.

Unveiling Singlet Fission Mediating States in TIPS-pentacene and its Aza Derivatives.

PubMed

Herz, Julia; Buckup, Tiago; Paulus, Fabian; Engelhart, Jens U; Bunz, Uwe H F; Motzkus, Marcus

2015-06-25

Femtosecond pump-depletion-probe experiments were carried out in order to shed light on the ultrafast excited-state dynamics of triisopropylsilylethynyl (TIPS)-pentacene and two nitrogen-containing derivatives, namely, diaza-TIPS-pentacene and tetraaza-TIPS-pentacene. Measurements performed in the visible and near-infrared spectral range in combination with rate model simulations reveal that singlet fission proceeds via the extremely short-lived intermediate (1)TT state, which absorbs in the near-infrared spectral region only. The T1 → T3 transition probed in the visible region shows a rise time that comprises two components according to a consecutive reaction (S1 → (1)TT → T1). The incorporation of nitrogen atoms into the acene structure leads to shorter dynamics, but the overall triplet formation follows the same kinetic model. This is of particular importance, since experiments on tetraaza-TIPS-pentacene allow for investigation of the triplet state in the visible range without an overlapping singlet contribution. In addition, the pump-depletion-probe experiments show that the triplet absorption in the visible (T1 → T3) and near-infrared (T1 → T2) regions occurs from the same initial state, which was questioned in previous studies. Furthermore, an additional ultrafast transfer between the excited triplet states (T3 → T2) is identified, which is also in agreement with the rate model simulation. By applying depletion pulses, which are resonant with higher vibrational levels, we gain insight into internal vibrational energy redistribution processes within the triplet manifold. This additional information is of great relevance regarding the study of loss channels within these materials.

Single molecule spectroscopy reveals heterogeneous transport mechanisms for molecular ions in a polyelectrolyte polymer brush.

PubMed

Reznik, Carmen; Estillore, Nicel; Advincula, Rigoberto C; Landes, Christy F

2009-11-05

Single molecule polarization and fluorescence correlation spectroscopy were used to evaluate heterogeneous transport mechanisms of molecular ions within supported polyelectrolyte brushes. Modes of diffusive transport include periods of significantly restricted rotational motion, often maintained over tens of milliseconds; periods of fast molecular rotation; and occasional adsorption of fluorescent probe molecules in the brush. The studies reveal rapid switching between orientational states during each observed mode of motion. Through quantitative analysis of state occupation times, the rate constants for transitions from weakly associated to strongly associated states were extracted. Additionally, the pH dependence of the ion transport rates in the brush exhibits an abrupt, rather than continuous, trend. These single molecule studies demonstrate the presence of dynamic anisotropic interactions between the charged molecular probe and the polymer brush and provide experimental evidence of stimuli responsive switchable transport functionality in the polyelectrolyte brush.

Fluorescence studies with DNA probes: dynamic aspects of DNA structure and DNA-protein interactions

NASA Astrophysics Data System (ADS)

Millar, David P.; Carver, Theodore E.

1994-08-01

Time-resolved fluorescence measurements of optical probes incorporated at specific sites in DNA provides a new approach to studies of DNA structure and DNA:protein interactions. This approach can be used to study complex multi-state behavior, such as the folding of DNA into alternative higher order structures or the transfer of DNA between multiple binding sites on a protein. In this study, fluorescence anisotropy decay of an internal dansyl probe attached to 17/27-mer oligonucleotides was used to monitor the distribution of DNA 3' termini bound at either the polymerase of 3' to 5' exonuclease sites of the Klenow fragment of DNA polymerase I. Partitioning of the primer terminus between the two active sites of the enzyme resulted in a heterogeneous probe environment, reflected in the associative behavior of the fluorescence anisotropy decay. Analysis of the anisotropy decay with a two state model of solvent-exposed and protein-associated dansyl probes was used to determine the fraction of DNA bound at each site. We examined complexes of Klenow fragment with DNAs containing various base mismatches. Single mismatches at the primer terminus caused a 3-fold increase in the equilibrium partitioning of DNA into the exonuclease site, while two or more consecutive G:G mismatches caused the DNA to bind exclusively at the exonuclease site, with a partitioning constant at least 250- fold greater than that of the corresponding matched DNA sequence. Internal single mismatches located up to four bases from the primer terminus produced larger effects than the same mismatch at the primer terminus. These results provide insight into the recognition mechanisms that enable DNA polymerases to proofread misincorporated bases during DNA replication.

Dynamics of exciton relaxation in LH2 antenna probed by multipulse nonlinear spectroscopy.

PubMed

Novoderezhkin, Vladimir I; Cohen Stuart, Thomas A; van Grondelle, Rienk

2011-04-28

We explain the relaxation dynamics in the LH2-B850 antenna as revealed by multipulse pump-dump-probe spectroscopy (Th. A. Cohen Stuart, M. Vengris, V. I. Novoderezhkin, R. J. Cogdell, C. N. Hunter, R. van Grondelle, submitted). The theory of pump-dump-probe response is evaluated using the doorway-window approach in combination with the modified Redfield theory. We demonstrate that a simultaneous fit of linear spectra, pump-probe, and pump-dump-probe kinetics can be obtained at a quantitative level using the disordered exciton model, which is essentially the same as used to model the spectral fluctuations in single LH2 complexes (Novoderezhkin, V.; Rutkauskas, D.; van Grondelle, R. Biophys. J. 2006, 90, 2890). The present studies suggest that the observed relaxation rates are strongly dependent on the realization of the disorder. A big spread of the rates (exceeding 3 orders of magnitude) is correlated with the disorder-induced changes in delocalization length and overlap of the exciton wave functions. We conclude that the bulk kinetics reflect a superposition of many pathways corresponding to different physical limits of energy transfer, varying from sub-20 fs relaxation between delocalized and highly spatially overlapping exciton states to >20 ps jumps between states localized at the opposite sides of the ring.

Development of a Methodology for the Characterisation of Air-coupled Ultrasound Probes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pietroni, Paolo; Marco Revel, Gian

2010-05-28

This study is aimed at developing a technique for the characterisation of air-coupled ultrasound probes, starting from the analysis of the mechanical behaviour of the probe membrane. The vibratory behaviour of the emission membrane is studied using laser-Doppler vibrometry techniques with high frequency demodulation system (20 MHz). The determination of the vibration provides information which are useful for the assessment of the performance of the probe, in particular concerning the Quality factor and the portion of the membrane which really contributes to the emission. During the second step the results of the vibration measurements are used to calculate, by meansmore » of numerical boundary element method, the ultrasound beam emitted in terms of intensity in space. The obtained field is compared with the direct measurements carried out by scanning with the receiver probe and a pinhole plate. This comparison allows the potential and the problems of the two different characterisation techniques to be determined, even if the pinhole technique (which is currently considered the state of the art) cannot be used as an absolute reference. This study appears to be useful for paving the way for a new methodology for the calibration of air-coupled ultrasound probes, which potentially could be used not only to improve the probe manufacturing process, but also to control conformity to specifications.« less

The Nanocrystalline State of Narrow Gap Semiconducting Chalcogenides

DTIC Science & Technology

2010-08-23

using a 1 nm scanning probe and the EDS microanalysis . For Annealing studies nanocrystal powder samples were placed in ceramic crucibles and annealed...nanocrystals are homogenous single phase EDS spectral images were collected in scanning transmission electron microcopy using a 1 nm electron probe...explorations with alio-valent elements (e.g. Sb3+, Ag+ doping in PbTe). • Perform chemical and physical characterization to demonstrate that nanocrystals are

ParseCNV integrative copy number variation association software with quality tracking

PubMed Central

Glessner, Joseph T.; Li, Jin; Hakonarson, Hakon

2013-01-01

A number of copy number variation (CNV) calling algorithms exist; however, comprehensive software tools for CNV association studies are lacking. We describe ParseCNV, unique software that takes CNV calls and creates probe-based statistics for CNV occurrence in both case–control design and in family based studies addressing both de novo and inheritance events, which are then summarized based on CNV regions (CNVRs). CNVRs are defined in a dynamic manner to allow for a complex CNV overlap while maintaining precise association region. Using this approach, we avoid failure to converge and non-monotonic curve fitting weaknesses of programs, such as CNVtools and CNVassoc, and although Plink is easy to use, it only provides combined CNV state probe-based statistics, not state-specific CNVRs. Existing CNV association methods do not provide any quality tracking information to filter confident associations, a key issue which is fully addressed by ParseCNV. In addition, uncertainty in CNV calls underlying CNV associations is evaluated to verify significant results, including CNV overlap profiles, genomic context, number of probes supporting the CNV and single-probe intensities. When optimal quality control parameters are followed using ParseCNV, 90% of CNVs validate by polymerase chain reaction, an often problematic stage because of inadequate significant association review. ParseCNV is freely available at http://parsecnv.sourceforge.net. PMID:23293001

ParseCNV integrative copy number variation association software with quality tracking.

PubMed

Glessner, Joseph T; Li, Jin; Hakonarson, Hakon

2013-03-01

A number of copy number variation (CNV) calling algorithms exist; however, comprehensive software tools for CNV association studies are lacking. We describe ParseCNV, unique software that takes CNV calls and creates probe-based statistics for CNV occurrence in both case-control design and in family based studies addressing both de novo and inheritance events, which are then summarized based on CNV regions (CNVRs). CNVRs are defined in a dynamic manner to allow for a complex CNV overlap while maintaining precise association region. Using this approach, we avoid failure to converge and non-monotonic curve fitting weaknesses of programs, such as CNVtools and CNVassoc, and although Plink is easy to use, it only provides combined CNV state probe-based statistics, not state-specific CNVRs. Existing CNV association methods do not provide any quality tracking information to filter confident associations, a key issue which is fully addressed by ParseCNV. In addition, uncertainty in CNV calls underlying CNV associations is evaluated to verify significant results, including CNV overlap profiles, genomic context, number of probes supporting the CNV and single-probe intensities. When optimal quality control parameters are followed using ParseCNV, 90% of CNVs validate by polymerase chain reaction, an often problematic stage because of inadequate significant association review. ParseCNV is freely available at http://parsecnv.sourceforge.net.

Development of Active DNA Control Technique for DNA Sequencer With a Solid-state Nanopore

NASA Astrophysics Data System (ADS)

Akahori, Rena; Harada, Kunio; Goto, Yusuke; Yanagi, Itaru; Yokoi, Takahide; Oura, Takeshi; Shibahara, Masashi; Takeda, Ken-Ichi

We have developed a technique that can control the arbitrary speeds of DNA passing through a solid-state nanopore of a DNA sequencer. For this active DNA control technique, we used a DNA-immobilized Si probe, larger than the membrane with a nanopore, and used a piezoelectric actuator and stepper motor to drive the probe. This probe enables a user to adjust the relative position between the nanopore and DNA immobilized on the probe without the need for precise lateral control. In this presentation, we demonstrate how DNA (block copolymer ([(dT)25-(dC)25-(dA)50]m)), immobilized on the probe, slid through a nanopore and was pulled out using the active DNA control technique. As the DNA-immobilized probe was being pulled out, we obtained various ion-current signal levels corresponding to the number of different nucleotides in a single strand of DNA.

Ultrafast dynamics of localized magnetic moments in the unconventional Mott insulator Sr 2IrO 4

DOE PAGES

Krupin, O.; Dakovski, G. L.; Kim, B. J.; ...

2016-06-16

Here, we report a time-resolved study of the ultrafast dynamics of the magnetic moments formed by themore » $${{J}_{\\text{eff}}}=1/2$$ states in Sr 2IrO 4 by directly probing the localized iridium 5d magnetic state through resonant x-ray diffraction. Using optical pump–hard x-ray probe measurements, two relaxation time scales were determined: a fast fluence-independent relaxation is found to take place on a time scale of 1.5 ps, followed by a slower relaxation on a time scale of 500 ps–1.5 ns.« less

Probing Surface Electric Field Noise with a Single Ion

DTIC Science & Technology

2013-07-30

potentials is housed inside a Faraday cage providing more than 40 dB of attenuation for electromagnetic fields in the range of frequencies between 200...and measuring the ion quantum state [16]. Thus, by measuring the effect of electric field noise on the motional quantum state of the ion, one can probe...understand these effects . In summary, we have probed the electric field noise near an aluminum-copper surface at room temperature using a single trapped ion

Low-energy d-d excitations in MnO studied by resonant x-ray fluorescence spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Butorin, S.M.; Guo, J.; Magnuson, M.

1997-04-01

Resonant soft X-ray emission spectroscopy has been demonstrated to possess interesting abilities for studies of electronic structure in various systems, such as symmetry probing, alignment and polarization dependence, sensitivity to channel interference, etc. In the present abstract the authors focus on the feasibility of resonant soft X-ray emission to probe low energy excitations by means of resonant electronic X-ray Raman scattering. Resonant X-ray emission can be regarded as an inelastic scattering process where a system in the ground state is transferred to a low excited state via a virtual core excitation. The energy closeness to a core excitation of themore » exciting radiation enhances the (generally) low probability for inelastic scattering at these wavelengths. Therefore soft X-ray emission spectroscopy (in resonant electronic Raman mode) can be used to study low energy d-d excitations in transition metal systems. The involvement of the intermediate core state allows one to use the selection rules of X-ray emission, and the appearance of the elastically scattered line in the spectra provides the reference to the ground state.« less

Ultrafast dynamics of isolated model photoactive yellow protein chromophores: "Chemical perturbation theory" in the laboratory.

PubMed

Vengris, Mikas; Larsen, Delmar S; van der Horst, Michael A; Larsen, Olaf F A; Hellingwerf, Klaas J; van Grondelle, Rienk

2005-03-10

Pump-probe and pump-dump probe experiments have been performed on several isolated model chromophores of the photoactive yellow protein (PYP). The observed transient absorption spectra are discussed in terms of the spectral signatures ascribed to solvation, excited-state twisting, and vibrational relaxation. It is observed that the protonation state has a profound effect on the excited-state lifetime of p-coumaric acid. Pigments with ester groups on the coumaryl tail end and charged phenolic moieties show dynamics that are significantly different from those of other pigments. Here, an unrelaxed ground-state intermediate could be observed in pump-probe signals. A similar intermediate could be identified in the sinapinic acid and in isomerization-locked chromophores by means of pump-dump probe spectroscopy; however, in these compounds it is less pronounced and could be due to ground-state solvation and/or vibrational relaxation. Because of strong protonation-state dependencies and the effect of electron donor groups, it is argued that charge redistribution upon excitation determines the twisting reaction pathway, possibly through interaction with the environment. It is suggested that the same pathway may be responsible for the initiation of the photocycle in native PYP.

Human Episodic Memory Retrieval Is Accompanied by a Neural Contiguity Effect.

PubMed

Folkerts, Sarah; Rutishauser, Ueli; Howard, Marc W

2018-04-25

Cognitive psychologists have long hypothesized that experiences are encoded in a temporal context that changes gradually over time. When an episodic memory is retrieved, the state of context is recovered-a jump back in time. We recorded from single units in the medial temporal lobe of epilepsy patients performing an item recognition task. The population vector changed gradually over minutes during presentation of the list. When a probe from the list was remembered with high confidence, the population vector reinstated the temporal context of the original presentation of that probe during study, a neural contiguity effect that provides a possible mechanism for behavioral contiguity effects. This pattern was only observed for well remembered probes; old probes that were not well remembered showed an anti-contiguity effect. These results constitute the first direct evidence that recovery of an episodic memory in humans is associated with retrieval of a gradually changing state of temporal context, a neural "jump back in time" that parallels the act of remembering. SIGNIFICANCE STATEMENT Episodic memory is the ability to relive a specific experience from one's life. For decades, researchers have hypothesized that, unlike other forms of memory that can be described as simple associations between stimuli, episodic memory depends on the recovery of a neural representation of spatiotemporal context. During study of a sequence of stimuli, the brain state of epilepsy patients changed slowly over at least a minute. When the participant remembered a particular event from the list, this gradually changing state was recovered. This provides direct confirmation of the prediction from computational models of episodic memory. The resolution of this point means that the study of episodic memory can focus on the mechanisms by which this representation of spatiotemporal context is maintained and sometimes recovered. Copyright © 2018 the authors 0270-6474/18/384200-12$15.00/0.

Observation of excited state charge transfer with fs/ps-CARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Blom, Alex Jason

2009-01-01

Excited state charge transfer processes are studied using the fs/ps-CARS probe technique. This probe allows for multiplexed detection of Raman active vibrational modes. Systems studied include Michler's Ketone, Coumarin 120, 4-dimethylamino-4'-nitrostilbene, and several others. The vibrational spectrum of the para di-substituted benzophenone Michler's Ketone in the first excited singlet state is studied for the first time. It is found that there are several vibrational modes indicative of structural changes of the excited molecule. A combined experimental and theoretical approach is used to study the simplest 7-amino-4-methylcoumarin, Coumarin 120. Vibrations observed in FTIR and spontaneous Raman spectra are assigned using densitymore » functional calculations and a continuum solvation model is used to predict how observed modes are affected upon inclusion of a solvent. The low frequency modes of the excited state charge transfer species 4-dimethylamino-4{prime}-nitrostilbene are studied in acetonitrile. Results are compared to previous work on this molecule in the fingerprint region. Finally, several partially completed projects and their implications are discussed. These include the two photon absorption of Coumarin 120, nanoconfinement in cyclodextrin cavities and sensitization of titania nanoparticles.« less

Alignment, vibronic level splitting, and coherent coupling effects on the pump-probe polarization anisotropy.

PubMed

Smith, Eric R; Jonas, David M

2011-04-28

The pump-probe polarization anisotropy is computed for molecules with a nondegenerate ground state, two degenerate or nearly degenerate excited states with perpendicular transition dipoles, and no resonant excited-state absorption. Including finite pulse effects, the initial polarization anisotropy at zero pump-probe delay is predicted to be r(0) = 3/10 with coherent excitation. During pulse overlap, it is shown that the four-wave mixing classification of signal pathways as ground or excited state is not useful for pump-probe signals. Therefore, a reclassification useful for pump-probe experiments is proposed, and the coherent anisotropy is discussed in terms of a more general transition dipole and molecular axis alignment instead of experiment-dependent ground- versus excited-state pathways. Although coherent excitation enhances alignment of the transition dipole, the molecular axes are less aligned than for a single dipole transition, lowering the initial anisotropy. As the splitting between excited states increases beyond the laser bandwidth and absorption line width, the initial anisotropy increases from 3/10 to 4/10. Asymmetric vibrational coordinates that lift the degeneracy control the electronic energy gap and off-diagonal coupling between electronic states. These vibrations dephase coherence and equilibrate the populations of the (nearly) degenerate states, causing the anisotropy to decay (possibly with oscillations) to 1/10. Small amounts of asymmetric inhomogeneity (2 cm(-1)) cause rapid (130 fs) suppression of both vibrational and electronic anisotropy beats on the excited state, but not vibrational beats on the ground electronic state. Recent measurements of conical intersection dynamics in a silicon napthalocyanine revealed anisotropic quantum beats that had to be assigned to asymmetric vibrations on the ground electronic state only [Farrow, D. A.; J. Chem. Phys. 2008, 128, 144510]. Small environmental asymmetries likely explain the observed absence of excited-state asymmetric vibrations in those experiments.

Positron surface state as a spectroscopic probe for characterizing surfaces of topological insulator materials

NASA Astrophysics Data System (ADS)

Callewaert, Vincent; Shastry, K.; Saniz, Rolando; Makkonen, Ilja; Barbiellini, Bernardo; Assaf, Badih A.; Heiman, Donald; Moodera, Jagadeesh S.; Partoens, Bart; Bansil, Arun; Weiss, A. H.

2016-09-01

Topological insulators are attracting considerable interest due to their potential for technological applications and as platforms for exploring wide-ranging fundamental science questions. In order to exploit, fine-tune, control, and manipulate the topological surface states, spectroscopic tools which can effectively probe their properties are of key importance. Here, we demonstrate that positrons provide a sensitive probe for topological states and that the associated annihilation spectrum provides a technique for characterizing these states. Firm experimental evidence for the existence of a positron surface state near Bi2Te2Se with a binding energy of Eb=2.7 ±0.2 eV is presented and is confirmed by first-principles calculations. Additionally, the simulations predict a significant signal originating from annihilation with the topological surface states and show the feasibility to detect their spin texture through the use of spin-polarized positron beams.

Polarization-dependent responses of fluorescent indicators partitioned into myelinated axons

NASA Astrophysics Data System (ADS)

Micu, Ileana; Brideau, Craig; Stys, Peter K.

2012-02-01

Myelination, i.e. the wrapping of axons in multiple layers of lipid-rich membrane, is a unique phenomenon in the nervous systems of both vertebrates and invertebrates, that greatly increases the speed and efficiency of signal transmission. In turn, disruption of axo-myelinic integrity underlies disability in numerous clinical disorders. The dependence of myelin physiology on nanometric organization of its lamellae makes it difficult to accurately study this structure in the living state. We expected that fluorescent probes might become highly oriented when partitioned into the myelin sheath, and in turn, this anisotropy could be interrogated by controlling the polarization state of the exciting laser field used for 2-photon excited fluorescence (TPEF). Live ex vivo myelinated rodent axons were labeled with a series of lipohilic and hydrophilic fluorescenct probes, and TPEF images acquired while laser polarization was varied at the sample over a broad range of ellipticities and orientations of the major angle [see Brideau, Micu & Stys, abstract this meeting]. We found that most probes exhibited strong dependence on both the major angle of polarization, and perhaps more surprisingly, on ellipticity as well. Lipophilic vs. hydrophilic probes exhibited distinctly different behavior. We propose that polarization-dependent TPEF microscopy represents a powerful tool for probing the nanostructural architecture of both myelin and axonal cytoskeleton in a domain far below the resolution limit of visible light microscopy. By selecting probes with different sizes and physicochemical properties, distinct aspects of cellular nanoarchitecture can be accurately interrogated in real-time in living tissue.

Free flux flow: a probe into the field dependence of vortex core size in clean single crystals

NASA Astrophysics Data System (ADS)

Gapud, A. A.; Gafarov, O.; Moraes, S.; Thompson, J. R.; Christen, D. K.; Reyes, A. P.

2012-02-01

The free-flux-flow (FFF) phase has been attained successfully in a number of clean, weak-pinning, low-anisotropy, low-Tc, single-crystal samples as a unique probe into type II superconductivity that is independent of composition. The ``clean'' quality of the samples have been confirmed by reversible magnetization, high residual resistivity ratio, and low critical current densities Jc with a re-entrant ``peak'' effect in Jc(H) just below the critical field Hc2. The necessity of high current densities presented technical challenges that had been successfully addressed, and FFF is confirmed by a field-dependent ohmic state that is also well below the normal state. In these studies, the FFF resistivity ρf(H) has been measured in order to observe the field-dependent core size of the quantized magnetic flux vortices as modeled recently by Kogan and Zelezhina (KZ) who predicted a specific deviation from Bardeen-Stephen flux flow, dependent on normalized temperature and scattering parameter λ. The compounds studied are: V3Si, LuNi2B2C, and NbSe2, and results have shown consistency with the KZ model. Other applications of this method could also be used to probe normal-state properties, especially for the new iron arsenides, as will be discussed.

Differential Enzyme Flexibility Probed Using Solid-State Nanopores.

PubMed

Hu, Rui; Rodrigues, João V; Waduge, Pradeep; Yamazaki, Hirohito; Cressiot, Benjamin; Chishti, Yasmin; Makowski, Lee; Yu, Dapeng; Shakhnovich, Eugene; Zhao, Qing; Wanunu, Meni

2018-05-22

Enzymes and motor proteins are dynamic macromolecules that coexist in a number of conformations of similar energies. Protein function is usually accompanied by a change in structure and flexibility, often induced upon binding to ligands. However, while measuring protein flexibility changes between active and resting states is of therapeutic significance, it remains a challenge. Recently, our group has demonstrated that breadth of signal amplitudes in measured electrical signatures as an ensemble of individual protein molecules is driven through solid-state nanopores and correlates with protein conformational dynamics. Here, we extend our study to resolve subtle flexibility variation in dihydrofolate reductase mutants from unlabeled single molecules in solution. We first demonstrate using a canonical protein system, adenylate kinase, that both size and flexibility changes can be observed upon binding to a substrate that locks the protein in a closed conformation. Next, we investigate the influence of voltage bias and pore geometry on the measured electrical pulse statistics during protein transport. Finally, using the optimal experimental conditions, we systematically study a series of wild-type and mutant dihydrofolate reductase proteins, finding a good correlation between nanopore-measured protein conformational dynamics and equilibrium bulk fluorescence probe measurements. Our results unequivocally demonstrate that nanopore-based measurements reliably probe conformational diversity in native protein ensembles.

A wavelength dependent investigation of the indole photophysics via ionization and fragmentation pump-probe spectroscopies.

PubMed

Godfrey, T J; Yu, Hui; Biddle, Michael S; Ullrich, Susanne

2015-10-14

A wavelength dependent study investigating the low-lying (1)La and (1)Lb states, both possessing (1)ππ* character, and the (1)πσ* state in the deactivation process of indole is presented here. Relaxation dynamics following excitation at 241, 250, 260, 270, 273, and 282 nm are examined using three gas-phase, pump-probe spectroscopic techniques: (1) hydrogen atom (H-atom) time-resolved kinetic energy release (TR-KER), (2) time-resolved photoelectron spectroscopy (TR-PES), and (3) time-resolved ion yield (TR-IY). Applied in combination, a more complete picture of the indole relaxation dynamics may be gleaned. For instance, TR-PES experiments directly observe all relaxation pathways by probing the evolution of the excited states following photoexcitation; whereas, TR-KER measurements indirectly, yet specifically, probe for (1)πσ*-state activity through the detection of H-atoms eliminated along the indole nitrogen-hydrogen (N-H) stretch coordinate-a possible outcome of (1)πσ*-state relaxation in indole. In addition, mass information obtained via TR-IY monitors fragmentation dynamics that may occur within the neutral electronically excited and/or cationic states. The work herein assesses the onset and importance of the (1)πσ* state at various pump wavelengths by systematically tuning across the ultraviolet absorption spectrum of indole with a particular focus on those pump wavelengths longer than 263 nm, where the involvement of the (1)πσ* state is under current debate. As far as this experimental work is concerned, there does not appear to be any significant involvement by the (1)πσ* state in the indole relaxation processes following excitation at 270, 273, or 282 nm. This investigation also evaluates the primary orbital promotions contributing to the (1)La, (1)Lb, and (1)πσ* transitions based on ionization preferences observed in TR-PES spectra. Relaxation time constants associated with dynamics along these states are also reported for excitation at all of the aforementioned pump wavelengths and are used to pinpoint the origin of the discrepancies found in the literature. In this context, advantages and disadvantages of the three experimental techniques are discussed.

Fluorescence Dynamics of a FRET Probe Designed for Crowding Studies.

PubMed

Currie, Megan; Leopold, Hannah; Schwarz, Jacob; Boersma, Arnold J; Sheets, Erin D; Heikal, Ahmed A

2017-06-15

Living cells are crowded with macromolecules and organelles. As a result, there is an urgent need for molecular sensors for quantitative, site-specific assessment of the macromolecular crowding effects on a myriad of biochemical processes toward quantitative cell biology and biophysics. Here we investigate the excited-state dynamics and translational diffusion of a novel FRET sensor (mCerulean-linker-mCitrine) in a buffer (PBS, pH 7.4) at room temperature. Complementary experiments were carried out on free CFP, YFP, and the cleaved FRET probe as controls. The wavelength-dependent fluorescence lifetime measurements of the donor and acceptor in the FRET probe, using the time-correlated single-photon counting technique, indicate an energy transfer efficiency of 6.8 ± 0.9% in PBS, with distinct excited-state dynamics from the recombinant CFP and YFP. The estimated mCerulean-mCitrine distance in this FRET probe is 7.7 ± 0.2 nm. The energy transfer efficiency increases (11.5 ± 0.9%) as the concentration of Ficoll-70 increases over the range of 0-300 g/L with an estimated mCerulean-mCitrine distance of 6.1 ± 0.2 nm. Complementary time-resolved anisotropy measurements suggest that the rotational diffusion of hetero-FRET in PBS is sensitive to the energy transfer from the donor to the acceptor. The results also suggest that the linker, -(GSG) 6 A(EAAAK) 6 A(GSG) 6 A(EAAAK) 6 A(GSG) 6 -, is rather flexible, and the observed rotational dynamics is likely to be due to a segmental mobility of the FRET pairs rather than an overall tumbling motion of a rigid probe. Comparative studies on a new construct of a FRET probe with a shorter, more flexible linker, mCerulean-(GSG) 18 -mCitrine, reveal enhanced energy transfer efficiency. On the millisecond time scale, fluorescence fluctuation analyses of the acceptor (excited at 488 nm) provide a means to examine the translational diffusion coefficient of the FRET probe. The results also suggest that the linker is flexible in this FRET probe, and the observed diffusion coefficient is faster than predicted as compared to the cleaved FRET probe. Our results serve as a point of reference for this FRET probe in a buffer toward its full potential as a sensor for macromolecular crowding in living cells and tissues.

Experimental validation of a theoretical model of dual wavelength photoacoustic (PA) excitation in fluorophores

NASA Astrophysics Data System (ADS)

Märk, Julia; Theiss, Christoph; Schmitt, Franz-Josef; Laufer, Jan

2015-03-01

Fluorophores, such as exogenous dyes and genetically expressed proteins, exhibit radiative relaxation with long excited state lifetimes. This can be exploited for PA detection based on dual wavelength excitation using pump and probe wavelengths that coincide with the absorption and emission spectra, respectively. While the pump pulse raises the fluorophore to a long-lived excited state, simultaneous illumination with the probe pulse reduces the excited state lifetime due to stimulated emission (SE).This leads to a change in thermalized energy, and hence PA signal amplitude, compared to single wavelength illumination. By introducing a time delay between pump and probe pulses, the change in PA amplitude can be modulated. Since the effect is not observed in endogenous chromophores, it provides a contrast mechanism for the detection of fluorophores via PA difference imaging. In this study, a theoretical model of the PA signal generation in fluorophores was developed and experimentally validated. The model is based on a system of coupled rate equations, which describe the spatial and temporal changes in the population of the molecular energy levels of a fluorophore as a function of pump-probe energy and concentration. This allows the prediction of the thermalized energy distribution, and hence the time-resolved PA signal amplitude. The model was validated by comparing its predictions to PA signals measured in solutions of rhodamine 6G, a well-known laser dye, and Atto680, a NIR fluorophore.

“Turn-on” fluorescence probe integrated polymer nanoparticles for sensing biological thiol molecules

NASA Astrophysics Data System (ADS)

Ang, Chung Yen; Tan, Si Yu; Lu, Yunpeng; Bai, Linyi; Li, Menghuan; Li, Peizhou; Zhang, Quan; Selvan, Subramanian Tamil; Zhao, Yanli

2014-11-01

A ``turn-on'' thiol-responsive fluorescence probe was synthesized and integrated into polymeric nanoparticles for sensing intracellular thiols. There is a photo-induced electron transfer process in the off state of the probe, and this process is terminated upon the reaction with thiol compounds. Configuration interaction singles (CIS) calculation was performed to confirm the mechanism of this process. A series of sensing studies were carried out, showing that the probe-integrated nanoparticles were highly selective towards biological thiol compounds over non-thiolated amino acids. Kinetic studies were also performed to investigate the relative reaction rate between the probe and the thiolated amino acids. Subsequently, the Gibbs free energy of the reactions was explored by means of the electrochemical method. Finally, the detection system was employed for sensing intracellular thiols in cancer cells, and the sensing selectivity could be further enhanced with the use of a cancer cell-targeting ligand in the nanoparticles. This development paves a path for the sensing and detection of biological thiols, serving as a potential diagnostic tool in the future.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kirkbride, James M. R.; Causier, Sarah K.; Dalton, Andrew R.

This paper details infra-red pump and probe studies on nitric oxide conducted with two continuous wave quantum cascade lasers both operating around 5 μm. The pump laser prepares a velocity selected population in a chosen rotational quantum state of the v = 1 level which is subsequently probed using a second laser tuned to a rotational transition within the v = 2 ← v = 1 hot band. The rapid frequency scan of the probe (with respect to the molecular collision rate) in combination with the velocity selective pumping allows observation of marked rapid passage signatures in the transient absorptionmore » profiles from the polarized vibrationally excited sample. These coherent transient signals are influenced by the underlying hyperfine structure of the pump and probe transitions, the sample pressure, and the coherent properties of the lasers. Pulsed pump and probe studies show that the transient absorption signals decay within 1 μs at 50 mTorr total pressure, reflecting both the polarization and population dephasing times of the vibrationally excited sample. The experimental observations are supported by simulation based upon solving the optical Bloch equations for a two level system.« less

Triplet-triplet energy transfer between luminescent probes bound to albumins

NASA Astrophysics Data System (ADS)

Mel'Nikov, A. G.; Saletskii, A. M.; Kochubey, V. I.; Pravdin, A. B.; Kurchatov, I. S.; Mel'Nikov, G. V.

2010-08-01

The interaction of polar and nonpolar luminescent probes with human blood serum albumins is studied by absorption and luminescence spectroscopy. It is found that the probes (polar eosin and nonpolar anthracene) can efficiently bind to proteins. The radii of the quenching spheres of energy-donor (eosin) triplet states in the presence of an acceptor (anthracene) in the process of the triplet-triplet energy transfer in proteins are determined for homogeneous and inhomogeneous distributions of acceptor molecules over the solution volume. It is shown that a decrease in the radius of the quenching sphere observed upon the addition of sodium dodecylsulfate surfactant is caused by structural changes in the protein.

Education Policies for Gender Equity: Probing into State Responses

ERIC Educational Resources Information Center

Stromquist, Nelly P.

2013-01-01

The implementation of non-discriminatory sex legislation provides theoretical and empirical grounds to examine responses by the state to gender equality. Tracing the trajectory of one such law in the U.S.--Title IX--over a period of 40 years, this study analyzes the extent to which the state: (1) acted as a unitary body, and (2) functioned to…

Probing Higgs-radion mixing in warped models through complementary searches at the LHC and the ILC

NASA Astrophysics Data System (ADS)

Frank, Mariana; Huitu, Katri; Maitra, Ushoshi; Patra, Monalisa

2016-09-01

We consider the Higgs-radion mixing in the context of warped space extradimensional models with custodial symmetry and investigate the prospects of detecting the mixed radion. Custodial symmetries allow the Kaluza-Klein excitations to be lighter and protect Z b b ¯ to be in agreement with experimental constraints. We perform a complementary study of discovery reaches of the Higgs-radion mixed state at the 13 and 14 TeV LHC and at the 500 and 1000 GeV International Linear Collider (ILC). We carry out a comprehensive analysis of the most significant production and decay modes of the mixed radion in the 80 GeV-1 TeV mass range and indicate the parameter space that can be probed at the LHC and the ILC. There exists a region of the parameter space which can be probed, at the LHC, through the diphoton channel even for a relatively low luminosity of 50 fb-1 . The reach of the four-lepton final state in probing the parameter space is also studied in the context of 14 TeV LHC, for a luminosity of 1000 fb-1 . At the ILC, with an integrated luminosity of 500 fb-1 , we analyze the Z -radion associated production and the W W fusion production, followed by the radion decay into b b ¯ and W+W-. The W W fusion production is favored over the Z -radion associated channel in probing regions of the parameter space beyond the LHC reach. The complementary study at the LHC and the ILC is useful both for the discovery of the radion and the understanding of its mixing sector.

Laser-muon spin spectroscopy in liquids - a technique to study the excited state chemistry of transients.

PubMed

Ghandi, Khashayar; Clark, Ian P; Lord, James S; Cottrell, Stephen P

2007-01-21

This study introduces laser-muon spin spectroscopy in the liquid phase, which extends muonium chemistry in liquids to the realm of excited states and enables the detection of muoniated molecules by their spin evolution after laser excitation. This leads to new opportunities to study the Kinetic Isotope Effects (KIEs) of muonium/atomic hydrogen reactions and to probe transient chemistry in radiolysis processes involved in muonium formation, as well as muoniated intermediates in excited states.

Nucleic acid probes in diagnostic medicine

NASA Technical Reports Server (NTRS)

Oberry, Phillip A.

1991-01-01

The need for improved diagnostic procedures is outlined and variations in probe technology are briefly reviewed. A discussion of the application of probe technology to the diagnosis of disease in animals and humans is presented. A comparison of probe versus nonprobe diagnostics and isotopic versus nonisotopic probes is made and the current state of sequence amplification is described. The current market status of nucleic acid probes is reviewed with respect to their diagnostic application in human and veterinary medicine. Representative product examples are described and information on probes being developed that offer promise as future products is discussed.

Effect of nuclear motion on molecular high order harmonic pump probe spectroscopy.

PubMed

Bredtmann, Timm; Chelkowski, Szczepan; Bandrauk, André D

2012-11-26

We study pump-probe schemes for the real time observation of electronic motion on attosecond time scale in the molecular ion H(2)(+) and its heavier isotope T(2)(+) while these molecules dissociate on femtosecond time scale by solving numerically the non-Born-Oppenheimer time-dependent Schrödinger equation. The UV pump laser pulse prepares a coherent superposition of the three lowest lying quantum states and the time-delayed mid-infrared, intense few-femtosecond probe pulse subsequently generates molecular high-order harmonics (MHOHG) from this coherent electron-nuclear wavepacket (CENWP). Varying the pump-probe time delay by a few hundreds of attoseconds, the MHOHG signal intensity is shown to vary by orders of magnitude. Due to nuclear movement, the coherence of these two upper states and the ground state is lost after a few femtoseconds and the MHOHG intensity variations as function of pump-probe delay time are shown to be equal to the period of electron oscillation in the coherent superposition of the two upper dissociative quantum states. Although this electron oscillation period and hence the periodicity of the harmonic spectra are quite constant over a wide range of internuclear distances, a strong signature of nuclear motion is seen in the actual shapes and ways in which these spectra change as a function of pump-probe delay time, which is illustrated by comparison of the MHOHG spectra generated by the two isotopes H(2)(+) and T(2)(+). Two different regimes corresponding roughly to internuclear distances R < 4a(0) and R > 4a(0) are identified: For R < 4a(0), the intensity of a whole range of frequencies in the plateau region is decreased by orders of magnitude when the delay time is changed by a few hundred attoseconds whereas in the cutoff region the peaks in the MHOHG spectra are red-shifted with increasing pump-probe time delay. For R > 4a(0), on the other hand, the peaks both in the cutoff and plateau region are red-shifted with increasing delay times with only slight variations in the peak intensities. A time-frequency analysis shows that in the case of a two-cycle probe pulse the sole contribution of one long and associated short trajectory correlates with the attenuation of a whole range of frequencies in the plateau region for R < 4a(0) whereas the observed red shift for R > 4a(0), even in the plateau region, correlates with a single electron return within one-half laser cycle.

Understanding API-polymer proximities in amorphous stabilized composite drug products using fluorine-carbon 2D HETCOR solid-state NMR.

PubMed

Abraham, Anuji; Crull, George

2014-10-06

A simple and robust method for obtaining fluorine-carbon proximities was established using a (19)F-(13)C heteronuclear correlation (HETCOR) two-dimensional (2D) solid-state nuclear magnetic resonance (ssNMR) experiment under magic-angle spinning (MAS). The method was applied to study a crystalline active pharmaceutical ingredient (API), avagacestat, containing two types of fluorine atoms and its API-polymer composite drug product. These results provide insight into the molecular structure, aid with assigning the carbon resonances, and probe API-polymer proximities in amorphous spray dried dispersions (SDD). This method has an advantage over the commonly used (1)H-(13)C HETCOR because of the large chemical shift dispersion in the fluorine dimension. In the present study, fluorine-carbon distances up to 8 Å were probed, giving insight into the API structure, crystal packing, and assignments. Most importantly, the study demonstrates a method for probing an intimate molecular level contact between an amorphous API and a polymer in an SDD, giving insights into molecular association and understanding of the role of the polymer in API stability (such as recrystallization, degradation, etc.) in such novel composite drug products.

Novel Single-Cell Analysis Platform Based on a Solid-State Zinc-Coadsorbed Carbon Quantum Dots Electrochemiluminescence Probe for the Evaluation of CD44 Expression on Breast Cancer Cells.

PubMed

Qiu, Youyi; Zhou, Bin; Yang, Xiaojuan; Long, Dongping; Hao, Yan; Yang, Peihui

2017-05-24

A novel single-cell analysis platform was fabricated using solid-state zinc-coadsorbed carbon quantum dot (ZnCQDs) nanocomposites as an electrochemiluminescence (ECL) probe for the detection of breast cancer cells and evaluation of the CD44 expression level. Solid-state ZnCQDs nanocomposite probes were constructed through the attachment of ZnCQDs to gold nanoparticles and then the loading of magnetic beads to amplify the ECL signal, exhibiting a remarkable 120-fold enhancement of the ECL intensity. Hyaluronic acid (HA)-functionalized solid-state probes were used to label a single breast cancer cell by the specific recognition of HA with CD44 on the cell surface, revealing more stable, sensitive, and effective tagging in comparison with the water-soluble CQDs. This strategy exhibited a good analytical performance for the analysis of MDA-MB-231 and MCF-7 single cells with linear range from 1 to 18 and from 1 to 12 cells, respectively. Furthermore, this single-cell analysis platform was used for evaluation of the CD44 expression level of these two cell lines, in which the MDA-MB-231 cells revealed a 2.8-5.2-fold higher CD44 expression level. A total of 20 single cells were analyzed individually, and the distributions of the ECL intensity revealed larger variations, indicating the high cellular heterogeneity of the CD44 expression level on the same cell line. The as-proposed single-cell analysis platform might provide a novel protocol to effectively study the individual cellular function and cellular heterogeneity.

Time-resolved orbital angular momentum spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Noyan, Mehmet A.; Kikkawa, James M.

We introduce pump-probe magneto-orbital spectroscopy, wherein Laguerre-Gauss optical pump pulses impart orbital angular momentum to the electronic states of a material and subsequent dynamics are studied with 100 fs time resolution. The excitation uses vortex modes that distribute angular momentum over a macroscopic area determined by the spot size, and the optical probe studies the chiral imbalance of vortex modes reflected off the sample. First observations in bulk GaAs yield transients that evolve on time scales distinctly different from population and spin relaxation, as expected, but with surprisingly large lifetimes.

Photoinduced molecular chirality probed by ultrafast resonant X-ray spectroscopy

DOE PAGES

Rouxel, Jérémy R.; Kowalewski, Markus; Mukamel, Shaul

2017-07-01

Recently developed circularly polarized X-ray light sources can probe the ultrafast chiral electronic and nuclear dynamics through spatially localized resonant core transitions. Here, we present simulations of time-resolved circular dichroism signals given by the difference of left and right circularly polarized X-ray probe transmission following an excitation by a circularly polarized optical pump with the variable time delay. Application is made to formamide which is achiral in the ground state and assumes two chiral geometries upon optical excitation to the first valence excited state. Probes resonant with various K-edges (C, N, and O) provide different local windows onto the paritymore » breaking geometry change thus revealing the enantiomer asymmetry.« less

Resolving phase information of the optical local density of state with scattering near-field probes

NASA Astrophysics Data System (ADS)

Prasad, R.; Vincent, R.

2016-10-01

We theoretically discuss the link between the phase measured using a scattering optical scanning near-field microscopy (s-SNOM) and the local density of optical states (LDOS). A remarkable result is that the LDOS information is directly included in the phase of the probe. Therefore by monitoring the spatial variation of the trans-scattering phase, we locally measure the phase modulation associated with the probe and the optical paths. We demonstrate numerically that a technique involving two-phase imaging of a sample with two different sized tips should allow to obtain the image the pLDOS. For this imaging method, numerical comparison with extinction probe measurement shows crucial qualitative and quantitative improvement.

Analysis and Design of a Fiber-optic Probe for DNA Sensors Final Report CRADA No. TSB-1147-95

DOE Office of Scientific and Technical Information (OSTI.GOV)

Molau, Nicole; Vail, Curtis

In 1995, a challenge in the field of genetics dealt with the acquisition of efficient DNA sequencing techniques for reading the 3 billion base-pairs that comprised the human genome. AccuPhotonics, Inc. proposed to develop and manufacture a state-of-the-art near-field scanning optical microscopy (NSOM) fiber-optic probe that was expected to increase probe efficiency by two orders of magnitude over the existing state-of-the-art and to improve resolution to 10Å. The detailed design calculation and optimization of electrical properties of the fiber-optic probe tip geometry would be performed at LLNL, using existing finite-difference time-domain (FDTD) electromagnetic (EM) codes.

Photoinduced molecular chirality probed by ultrafast resonant X-ray spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rouxel, Jérémy R.; Kowalewski, Markus; Mukamel, Shaul

Recently developed circularly polarized X-ray light sources can probe the ultrafast chiral electronic and nuclear dynamics through spatially localized resonant core transitions. Here, we present simulations of time-resolved circular dichroism signals given by the difference of left and right circularly polarized X-ray probe transmission following an excitation by a circularly polarized optical pump with the variable time delay. Application is made to formamide which is achiral in the ground state and assumes two chiral geometries upon optical excitation to the first valence excited state. Probes resonant with various K-edges (C, N, and O) provide different local windows onto the paritymore » breaking geometry change thus revealing the enantiomer asymmetry.« less

Collision Processes in Methyl Chloride

NASA Astrophysics Data System (ADS)

Pape, Travis W.

Time-resolved, double resonance spectroscopy using infrared pump radiation and millimeter-wave and submillimeter -wave probe radiation (IRMMDR) has been used to study rotational and vibrational collision processes in CH_3 ^{35}Cl and CH_3 ^{37}Cl. A collisional energy transfer model using only five parameters for rotational processes plus those needed for vibrational processes accurately models over 500 IRMMDR time responses for 105 pump-probe combinations, using three pump coincidences and a wide range of probed rotational states. Previous studies in this laboratory revealed that J- and K-changing rotational energy transfer (RET) have vastly different characteristics in CH_3 F. As was found for CH_3F, J-changing rotational collision rates in CH_3 Cl are modeled accurately by both the Statistical Power Gap law and the Infinite Order Sudden approximation using a power law expression for the basis rates. However, in contrast to CH_3F, where all IRMMDR time responses for K-changing collisions have the same shape, many time responses of CH_3 Cl states populated by K-changing collisions contain an additional early-time feature (ETF) that varies with pump and probe state. Nonetheless, a simple generalization of the previously reported model for K-changing collisions is shown to account for all of the additional features observed in CH_3Cl. Rather than observing a fixed temperature for K-changing collisions as was the case for CH_3F, the temperature is found to be a function of time for CH_3 Cl. Moreover, the two new parameters this adds to the RET model are related to known physical quantities. A qualitative argument of K-changing collisions based on a classical picture is offered to explain the difference between the measured J- and K-changing state-to-state rates in CH_3Cl. As was observed in CH_3F, the principal vibrational collision processes are the near -resonant V-swap process, in which two colliding molecules exchange a quantum of vibrational energy, and a nonresonant process that directly moves population from the pumped {bf v}_6 = 1 vibrational state to the {bf v}_3 = 1 vibrational state. A V to T/R process was also measured. Finally, a V-swap process was measured that populates vibrational states of the other isotopic species.

Pump-probe surface photovoltage spectroscopy measurements on semiconductor epitaxial layers.

PubMed

Jana, Dipankar; Porwal, S; Sharma, T K; Kumar, Shailendra; Oak, S M

2014-04-01

Pump-probe Surface Photovoltage Spectroscopy (SPS) measurements are performed on semiconductor epitaxial layers. Here, an additional sub-bandgap cw pump laser beam is used in a conventional chopped light geometry SPS setup under the pump-probe configuration. The main role of pump laser beam is to saturate the sub-bandgap localized states whose contribution otherwise swamp the information related to the bandgap of material. It also affects the magnitude of Dember voltage in case of semi-insulating (SI) semiconductor substrates. Pump-probe SPS technique enables an accurate determination of the bandgap of semiconductor epitaxial layers even under the strong influence of localized sub-bandgap states. The pump beam is found to be very effective in suppressing the effect of surface/interface and bulk trap states. The overall magnitude of SPV signal is decided by the dependence of charge separation mechanisms on the intensity of the pump beam. On the contrary, an above bandgap cw pump laser can be used to distinguish the signatures of sub-bandgap states by suppressing the band edge related feature. Usefulness of the pump-probe SPS technique is established by unambiguously determining the bandgap of p-GaAs epitaxial layers grown on SI-GaAs substrates, SI-InP wafers, and p-GaN epilayers grown on Sapphire substrates.

What can we learn from relaxation measurements of a laser-perturbed atmosphere? A modeling study

NASA Technical Reports Server (NTRS)

Clericetti, Agostino; Vandenbergh, Hubert; Rossi, Michel J.

1994-01-01

The chemical kinetic aspects of a transient increase in OH and HO2 by several orders of magnitude are explored in three model tropospheres. This chemical kinetic modeling effort was undertaken to support the operation of a pump-and-probe LIDAR instrument. A powerful excimer laser pulse perturbs the troposphere after which its relaxation back to steady state is examined by remote sensing, for example by DIAL or LIF. Instead of probing ambient levels of key free radicals, a study of the relaxation kinetics in real time enables chemical mechanistic studies in situ.

The CritiView: a new fiber optic based optical device for the assessment of tissue vitality

NASA Astrophysics Data System (ADS)

Mayevsky, Avraham; Blum, Yoram; Dekel, Nava; Deutsch, Assaf; Halfon, Rafael; Kremer, Shlomi; Pewzner, Eliyahu; Sherman, Efrat; Barnea, Ofer

2006-02-01

The most important parameter that reflects the balance between oxygen supply and demand in tissues is the mitochondrial NADH redox state that could be monitored In vivo. Nevertheless single parameter monitoring is limited in the interpretation capacity of the very complicated pathophysiological events, therefore three more parameters were added to the NADH and the multiparametric monitoring system was used in experimental and clinical studies. In our previous paper1 we described the CritiView (CRV1) including a fiber optic probe that monitor four physiological parameters in real time. In the new model (CRV3) several factors such as UV safety, size and price of the device were improved significantly. The CRV3 enable to monitor the various parameters in three different locations in the tissue thus increasing the reliability of the data due to the better statistics. The connection between the device and the monitored tissue could be done by various types of probes. The main probe that was tested also in clinical studies was a special 3 points probe that includes 9 optical fibers (3 in each point) that was embedded in a three way Foley catheter. This catheter enabled the monitoring of urethral wall vitality as an indicator of the development of body metabolic emergency state. The three point probe was tested in the brain exposed to the lack of oxygen (Anoxia, Hypoxia or Ischemia). A decrease in blood oxygenation and a large increase in mitochondrial NADH fluorescence were recorded. The microcirculatory blood flow increased during anoxia and hypoxia and decreased significantly under ischemia.

Spectral and photophysical properties of intramolecular charge transfer fluorescence probe: 4'-Dimethylamino-2,5-dihydroxychalcone

NASA Astrophysics Data System (ADS)

Xu, Zhicheng; Bai, Guan; Dong, Chuan

2005-12-01

The spectral and photophysical properties of a new intramolecular charge transfer (ICT) probe, namely 4'-dimethylamino-2,5-dihydroxychalcone (DMADHC) were studied in different solvents by using steady-state absorption and emission spectroscopy. Whereas the absorption spectrum undergoes minor change with increasing polarity of the solvents, the fluorescence spectrum experiences a distinct bathochromic shift in the band position and the fluorescence quantum yield increases reaching a maximum before decrease with increasing the solvent polarity. The magnitude of change in the dipole moment was calculated based on the Lippert-Mataga equation. These results give the evidence about the intramolecular charge transfer character in the emitting singlet state of this compound.

Spectral and photophysical properties of intramolecular charge transfer fluorescence probe: 4'-dimethylamino-2,5-dihydroxychalcone.

PubMed

Xu, Zhicheng; Bai, Guan; Dong, Chuan

2005-12-01

The spectral and photophysical properties of a new intramolecular charge transfer (ICT) probe, namely 4'-dimethylamino-2,5-dihydroxychalcone (DMADHC) were studied in different solvents by using steady-state absorption and emission spectroscopy. Whereas the absorption spectrum undergoes minor change with increasing polarity of the solvents, the fluorescence spectrum experiences a distinct bathochromic shift in the band position and the fluorescence quantum yield increases reaching a maximum before decrease with increasing the solvent polarity. The magnitude of change in the dipole moment was calculated based on the Lippert-Mataga equation. These results give the evidence about the intramolecular charge transfer character in the emitting singlet state of this compound.

Electron Paramagnetic Resonance Measurements of Reactive Oxygen Species by Cyclic Hydroxylamine Spin Probes.

PubMed

Dikalov, Sergey I; Polienko, Yuliya F; Kirilyuk, Igor

2018-05-20

Oxidative stress contributes to numerous pathophysiological conditions such as development of cancer, neurodegenerative, and cardiovascular diseases. A variety of measurements of oxidative stress markers in biological systems have been developed; however, many of these methods are not specific, can produce artifacts, and do not directly detect the free radicals and reactive oxygen species (ROS) that cause oxidative stress. Electron paramagnetic resonance (EPR) is a unique tool that allows direct measurements of free radical species. Cyclic hydroxylamines are useful and convenient molecular probes that readily react with ROS to produce stable nitroxide radicals, which can be quantitatively measured by EPR. In this work, we critically review recent applications of various cyclic hydroxylamine spin probes in biology to study oxidative stress, their advantages, and the shortcomings. Recent Advances: In the past decade, a number of new cyclic hydroxylamine spin probes have been developed and their successful application for ROS measurement using EPR has been published. These new state-of-the-art methods provide improved selectivity and sensitivity for in vitro and in vivo studies. Although cyclic hydroxylamine spin probes EPR application has been previously described, there has been lack of translation of these new methods into biomedical research, limiting their widespread use. This work summarizes "best practice" in applications of cyclic hydroxylamine spin probes to assist with EPR studies of oxidative stress. Additional studies to advance hydroxylamine spin probes from the "basic science" to biomedical applications are needed and could lead to better understanding of pathological conditions associated with oxidative stress. Antioxid. Redox Signal. 28, 1433-1443.

Periodically modulated dark states

NASA Astrophysics Data System (ADS)

Han, Yingying; Zhang, Jun; Zhang, Wenxian

2018-04-01

Phenomena of electromagnetically induced transparency (PEIT) may be interpreted by the Autler-Townes Splitting (ATS), where the coupled states are split by the coupling laser field, or by the quantum destructive interference (QDI), where the atomic phases caused by the coupling laser and the probe laser field cancel. We propose modulated experiments to explore the PEIT in an alternative way by periodically modulating the coupling and the probe fields in a Λ-type three-level system initially in a dark state. Our analytical and numerical results rule out the ATS interpretation and show that the QDI interpretation is more appropriate for the modulated experiments. Interestingly, dark state persists in the double-modulation situation where control and probe fields never occur simultaneously, which is significant difference from the traditional dark state condition. The proposed experiments are readily implemented in atomic gases, artificial atoms in superconducting quantum devices, or three-level meta-atoms in meta-materials.

Flavour fields in steady state: stress tensor and free energy

NASA Astrophysics Data System (ADS)

Banerjee, Avik; Kundu, Arnab; Kundu, Sandipan

2016-02-01

The dynamics of a probe brane in a given gravitational background is governed by the Dirac-Born-Infeld action. The corresponding open string metric arises naturally in studying the fluctuations on the probe. In Gauge-String duality, it is known that in the presence of a constant electric field on the worldvolume of the probe, the open string metric acquires an event horizon and therefore the fluctuation modes on the probe experience an effective temperature. In this article, we bring together various properties of such a system to a formal definition and a subsequent narration of the effective thermodynamics and the stress tensor of the corresponding flavour fields, also including a non-vanishing chemical potential. In doing so, we point out a potentially infinitely-degenerate scheme-dependence of regularizing the free energy, which nevertheless yields a universal contribution in certain cases. This universal piece appears as the coefficient of a log-divergence in free energy when a space-filling probe brane is embedded in AdS d+1-background, for d = 2, 4, and is related to conformal anomaly. For the special case of d = 2, the universal factor has a striking resemblance to the well-known heat current formula in (1 + 1)-dimensional conformal field theory in steady-state, which endows a plausible physical interpretation to it. Interestingly, we observe a vanishing conformal anomaly in d = 6.

Preparation and preliminary characterization of crystallizing fluorescent derivatives of chicken egg white lysozyme

NASA Astrophysics Data System (ADS)

Sumida, John P.; Forsythe, Elizabeth L.; Pusey, Marc L.

2001-11-01

Fluorescence is one of the most versatile and powerful tools for the study of macromolecules. While most proteins are intrinsically fluorescent, working at crystallization concentrations require the use of covalently prepared derivatives added as tracers. This approach requires derivatives that do not markedly affect the crystal packing. We have prepared fluorescent derivatives of chicken egg white lysozyme with probes bound to one of two different sites on the protein molecule. Lucifer yellow and 5-(2-aminoethyl)aminonapthalene-1-sulfonic acid (EDANS) have been attached to the side chain carboxyl of Asp 101 using a carbodiimide coupling procedure. Asp 101 lies within the active site cleft, and it is believed that the probes are "buried" within that cleft. Lucifer yellow and EDANS probes with iodoacetamide reactive groups have been bound to His 15, located on the "back side" of the molecule relative to the active site. All the derivatives fluoresce in the solution and the crystalline states. Fluorescence characterization has focused on determination of binding effects on the probe quantum yield, lifetime, absorption and emission spectra, and quenching by added solutes. Quenching studies show that, as postulated, the Asp 101-bound probes are partially sheltered from the bulk solution by their location within the active site cleft. Probes bound to His 15 have quenching constants about equal to those for the free probes, indicating that this site is highly exposed to the bulk solution.

Probe for Sampling of Interstitial Fluid From Bone

NASA Technical Reports Server (NTRS)

Janle, Elsa M.

2004-01-01

An apparatus characterized as both a membrane probe and a bone ultrafiltration probe has been developed to enable in vivo sampling of interstitial fluid in bone. The probe makes it possible to measure the concentration of calcium and other constituents of the fluid that may be relevant to bone physiology. The probe could be especially helpful in experimental studies of microgravitational bone loss and of terrestrial bone-loss disease states, including osteoporosis. The probe can be implanted in the bone tissue of a living animal and can be used to extract samples of the interstitial bone fluid from time to time during a long-term study. The probe includes three 12-cm-long polyacrylonitrile fibers configured in a loop form and attached to polyurethane tubing [inside diameter 0.025 in. (0.64 mm), outside diameter 0.040 in. (1 mm)]; the attachment is made by use of a 1-cm-long connecting piece of polyurethane tubing [inside diameter 0.035 0.003 in. (0.89 0.08 mm), outside diameter 0.060 0.003 in. (1.52 0.08 mm)]. At the distal end, a 2-cm-long piece of polyurethane tubing of the same inner and outer diameters serves as a connector to a hub. A 1-cm long piece of expanded poly (tetrafluoroethylene) tubing over the joint between the fibers and the connecting tubing serves as a tissue-in-growth site.

Reaction pathways of photoexcited retinal in proteorhodopsin studied by pump-dump-probe spectroscopy.

PubMed

Rupenyan, Alisa; van Stokkum, Ivo H M; Arents, Jos C; van Grondelle, Rienk; Hellingwerf, Klaas J; Groot, Marie Louise

2009-12-17

Proteorhodopsin (pR) is a membrane-embedded proton pump from the microbial rhodopsin family. Light absorption by its retinal chromophore initiates a photocycle, driven by trans/cis isomerization on the femtosecond to picosecond time scales. Here, we report a study on the photoisomerization dynamics of the retinal chromophore of pR, using dispersed ultrafast pump-dump-probe spectroscopy. The application of a pump pulse initiates the photocycle, and with an appropriately tuned dump pulse applied at a time delay after the dump, the molecules in the initial stages of the photochemical process can be de-excited and driven back to the ground state. In this way, we were able to resolve an intermediate on the electronic ground state that represents chromophores that are unsuccessful in isomerization. In particular, the fractions of molecules that undergo slow isomerization (20 ps) have a high probability to enter this state rather than the isomerized K-state. On the ground state reaction surface, return to the stable ground state conformation via a structural or vibrational relaxation occurs in 2-3 ps. Inclusion of this intermediate in the kinetic scheme led to more consistent spectra of the retinal-excited state, and to a more accurate estimation of the quantum yield of isomerization (Phi = 0.4 at pH 6).

A colorimetric turn-on optical chemosensor for Cu2+ ions and its application as solid state sensor

NASA Astrophysics Data System (ADS)

Pannipara, Mehboobali; Al-Sehemi, Abdullah G.; Assiri, Mohammed; Kalam, Abul

2018-05-01

We report a novel coumarin based optical chemosensor (Probe 1) for the selective and sensitive detection of Cu2+ ions in aqueous medium. The addition of Cu2+ ions to Probe 1 shows distinct color change from light yellow to pinkish red color under visible light with the sensing limit of 1.54 μM. Moreover, practical utility of Probe 1 as solid state optical sensor (test paper, TLC plates) for sensing Cu2+ has been demonstrated by instantaneous "naked eye" response.

A red-emitting indolium fluorescence probe for membranes - flavonoids interactions.

PubMed

Gao, Qingyun; Liu, Han; Ding, Qiongjie; Du, Jinya; Liu, Chunlin; Yang, Wei; Shen, Ping; Yang, Changying

2018-05-01

The red-emitting indolium derivative compound (E)-2-(4-(diphenylamino)styryl)-1,3,3-trimethyl-3H-indol-1-ium iodide (H3) was demonstrated as a sensitive membrane fluorescence probe. The probe located at the interface of liposomes when mixed showed much fluorescence enhancement by inhibiting the twisted intramolecular charge transfer state. After ultrasonic treatment, it penetrated into lipid bilayers with the emissions leveling off and a rather large encapsulation efficiency (71.4%) in liposomes. The ζ-potential and particle size measurement confirmed that the charged indolium group was embedded deeply into lipid bilayers. The probe was then used to monitor the affinities of antioxidant flavonoids for membranes. It was verified that quercetin easily interacted with liposomes and dissociated the probe from the internal lipid within 60 s under the condition of simply mixing. The assessment of binding affinities of six flavonoids and the coincident results with their antioxidation activities indicated that it was a promising membrane probe for the study of drug bio-affinities. Copyright © 2018 John Wiley & Sons, Ltd.

Excited state proton transfer in strongly enhanced GFP (sGFP2).

PubMed

van Oort, Bart; ter Veer, Mirelle J T; Groot, Marie Louise; van Stokkum, Ivo H M

2012-07-07

Proton transfer is an elementary process in biology. Green fluorescent protein (GFP) has served as an important model system to elucidate the mechanistic details of this reaction, because in GFP proton transfer can be induced by light absorption. We have used pump-dump-probe spectroscopy to study how proton transfer through the 'proton-wire' around the chromophore is affected by a combination of mutations in a modern GFP variety (sGFP2). The results indicate that in H(2)O, after absorption of a photon, a proton is transferred (A* → I*) in 5 ps, and back-transferred from a ground state intermediate (I → A) in 0.3 ns, similar to time constants found with GFPuv, although sGFP2 shows less heterogeneous proton transfer. This suggests that the mutations left the proton-transfer largely unchanged, indicating the robustness of the proton-wire. We used pump-dump-probe spectroscopy in combination with target analysis to probe suitability of the sGFP2 fluorophore for super-resolution microscopy.

Fiber-optic Singlet Oxygen [1O2 (1Δg)] Generator Device Serving as a Point Selective Sterilizer

PubMed Central

Aebisher, David; Zamadar, Matibur; Mahendran, Adaickapillai; Ghosh, Goutam; McEntee, Catherine; Greer, Alexander

2016-01-01

Traditionally, Type II heterogeneous photo-oxidations produce singlet oxygen via external irradiation of a sensitizer and external supply of ground-state oxygen. A potential improvement is reported here. A hollow-core fiber-optic device was developed with an “internal” supply of light and flowing oxygen, and a porous photosensitizer-end capped configuration. Singlet oxygen was delivered through the fiber tip. The singlet oxygen steady-state concentration in the immediate vicinity of the probe tip was ca 20 fM by N-benzoyl-DL-methionine trapping. The device is portable and the singlet oxygen-generating tip is maneuverable, which opened the door to simple disinfectant studies. Complete Escherichia coli inactivation was observed in 2 h when the singlet oxygen sensitizing probe tip was immersed in 0.1 mL aqueous samples of 0.1–4.4 × 107 cells. Photobleaching of the probe tip occurred after ca 12 h of use, requiring baking and sensitizer reloading steps for reuse. PMID:20497367

Spatially resolved NMR spectra for the Swiss cheese model in heavy fermion PuCoGa5 superconductor

NASA Astrophysics Data System (ADS)

Das, Tanmoy; Zhu, Jian-Xin; Balatsky, A. V.; Graf, M. J.

2011-03-01

Spatially resolved NMR experiments, which probe the local electronic excitations, play a vital role for studying the pairing symmetry of unconventional superconductors. Here we calculate the spatial modulation of the NMR spin-lattice relaxation rate (1/T1) for the Swiss cheese model as a function of impurity concentration in PuCoGa5 superconductor. The local suppression of the superconducting order parameter due to impurities is related to the number of holes in the Swiss cheese model. Our results indicate that Friedel-like oscillations,as seen in the local-density of states near an impurity, are also present in the behavior of 1/T1 as one moves away from the impurity site. We demonstrate that the gap nodes, which are filled by disorder, can be probed by NMR through the local information encoded in the spectra. The advantage of spatially resolved NMR compared to STM measurements is that the former probe is not sensitive to surface states. Work is supported by US DOE.

Weak-field few-femtosecond VUV photodissociation dynamics of water isotopologues

NASA Astrophysics Data System (ADS)

Baumann, Arne; Bazzi, Sophia; Rompotis, Dimitrios; Schepp, Oliver; Azima, Armin; Wieland, Marek; Popova-Gorelova, Daria; Vendrell, Oriol; Santra, Robin; Drescher, Markus

2017-07-01

We present a joint experimental and theoretical study of the VUV-induced dynamics of H2O and its deuterated isotopologues in the first excited state (A ˜1B1 ) utilizing a VUV-pump VUV-probe scheme combined with a b initio classical trajectory calculations. 16-fs VUV pulses centered at 161 nm created by fifth-order harmonic generation are employed for single-shot pump-probe measurements. Combined with a precise determination of the VUV pulses' temporal profile, they provide the necessary temporal resolution to elucidate sub-10-fs dissociation dynamics in the 1+1 photon ionization time window. Ionization with a single VUV photon complements established strong-field ionization schemes by disclosing the molecular dynamics under perturbative conditions. Kinetic isotope effects derived from the pump-probe experiment are found to be in agreement with our by ab initio classical trajectory calculations, taking into account photoionization cross sections for the ground and first excited state of the water cation.

Simulating pump-probe photoelectron and absorption spectroscopy on the attosecond timescale with time-dependent density functional theory.

PubMed

De Giovannini, Umberto; Brunetto, Gustavo; Castro, Alberto; Walkenhorst, Jessica; Rubio, Angel

2013-05-10

Molecular absorption and photoelectron spectra can be efficiently predicted with real-time time-dependent density functional theory. We show herein how these techniques can be easily extended to study time-resolved pump-probe experiments, in which a system response (absorption or electron emission) to a probe pulse is measured in an excited state. This simulation tool helps with the interpretation of fast-evolving attosecond time-resolved spectroscopic experiments, in which electronic motion must be followed at its natural timescale. We show how the extra degrees of freedom (pump-pulse duration, intensity, frequency, and time delay), which are absent in a conventional steady-state experiment, provide additional information about electronic structure and dynamics that improve characterization of a system. As an extension of this approach, time-dependent 2D spectroscopy can also be simulated, in principle, for large-scale structures and extended systems. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Coherent wavepackets in the Fenna-Matthews-Olson complex are robust to excitonic-structure perturbations caused by mutagenesis

NASA Astrophysics Data System (ADS)

Maiuri, Margherita; Ostroumov, Evgeny E.; Saer, Rafael G.; Blankenship, Robert E.; Scholes, Gregory D.

2018-02-01

Femtosecond pulsed excitation of light-harvesting complexes creates oscillatory features in their response. This phenomenon has inspired a large body of work aimed at uncovering the origin of the coherent beatings and possible implications for function. Here we exploit site-directed mutagenesis to change the excitonic level structure in Fenna-Matthews-Olson (FMO) complexes and compare the coherences using broadband pump-probe spectroscopy. Our experiments detect two oscillation frequencies with dephasing on a picosecond timescale—both at 77 K and at room temperature. By studying these coherences with selective excitation pump-probe experiments, where pump excitation is in resonance only with the lowest excitonic state, we show that the key contributions to these oscillations stem from ground-state vibrational wavepackets. These experiments explicitly show that the coherences—although in the ground electronic state—can be probed at the absorption resonances of other bacteriochlorophyll molecules because of delocalization of the electronic excitation over several chromophores.

Understanding students' explanations of biological phenomena: Conceptual frameworks or p-prims?

NASA Astrophysics Data System (ADS)

Southerland, Sherry A.; Abrams, Eleanor; Cummins, Catherine L.; Anzelmo, Julie

2001-07-01

This study explores two differing perspectives of the nature of students' biological knowledge structures, conceptual frameworks, and p-prims. Students from four grade levels and from three regions of the United States were asked to explain a variety of biological phenomena. Students' responses to the interview probes were analyzed to describe 1) patterns in the nature of students' explanations across grade levels and interview probes, and 2) the consistency of students' explanations across individual interview probes and across the range of probes. The results were interpreted from both perspectives of knowledge structures. While definitive assertions supporting either perspective could not be made, each hypothesis was explored. Although the more prevalent description of student conceptions within a broader conceptual framework could not be discounted, the p-prim of need as a rationale for change was also found to offer a useful description of knowledge frameworks for this content area. The difficulties endemic to the use of biology for the study of basic knowledge structures are also discussed.

Determining Confounding Sensitivities In Eddy Current Thin Film Measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gros, Ethan; Udpa, Lalita; Smith, James A.

Determining Confounding Sensitivities In Eddy Current Thin Film Measurements Ethan Gros, Lalita Udpa, Electrical Engineering, Michigan State University, East Lansing MI 48824 James A. Smith, Experiment Analysis, Idaho National Laboratory, Idaho Falls ID 83415 Eddy current (EC) techniques are widely used in industry to measure the thickness of non-conductive films on a metal substrate. This is done using a system whereby a coil carrying a high-frequency alternating current is used to create an alternating magnetic field at the surface of the instrument's probe. When the probe is brought near a conductive surface, the alternating magnetic field will induce ECs inmore » the conductor. The substrate characteristics and the distance of the probe from the substrate (the coating thickness) affect the magnitude of the ECs. The induced currents load the probe coil affecting the terminal impedance of the coil. The measured probe impedance is related to the lift off between coil and conductor as well as conductivity of the test sample. For a known conductivity sample, the probe impedance can be converted into an equivalent film thickness value. The EC measurement can be confounded by a number of measurement parameters. It is the goal of this research to determine which physical properties of the measurement set-up and sample can adversely affect the thickness measurement. The eddy current testing is performed using a commercially available, hand held eddy current probe (ETA3.3H spring loaded eddy probe running at 8 MHz) that comes with a stand to hold the probe. The stand holds the probe and adjusts the probe on the z-axis to help position the probe in the correct area as well as make precise measurements. The signal from the probe is sent to a hand held readout, where the results are recorded directly in terms of liftoff or film thickness. Understanding the effect of certain factors on the measurements of film thickness, will help to evaluate how accurate the ETA3.3H spring loaded eddy probe is at measuring film thickness under varying experimental conditions. This research will study the effects of a number of factors such as i) calibration, ii) conductivity, iii) edge effect, iv) surface finish of base material and v) cable condition and compare with the long term reproducibility of a standard measurement. This work was performed with support from the Department of Energy under the United States National Nuclear Security Administration (NNSA) at the Idaho National Laboratory.« less

Flexible high-temperature pH probe

DOEpatents

Bielawski, John C.; Outwater, John O.; Halbfinger, George P.

2003-04-22

A flexible pH probe device is provided for use in hot water and other high temperature environments up to about 590.degree. F. The pH probe includes a flexible, inert tubular probe member, an oxygen anion conducting, solid state electrolyte plug located at the distal end of the tubular member, oxide powder disposed at the distal end of the tubular member; a metal wire extending along the tubular member and having a distal end in contact with the oxide powder so as to form therewith an internal reference electrode; and a compression fitting forming a pressure boundary seal around a portion of the tubular member remote from the distal end thereof. Preferably, the tubular member is made of polytetrafluoroethylene, and the solid state electrolyte plug is made of stabilized zirconia. The flexibility of the probe member enables placement of the electrode into the area of interest, including around corners, into confined areas and the like.

The interaction of amino acids with macrocyclic pH probes of pseudopeptidic nature.

PubMed

Izquierdo, M Angeles; Wadhavane, Prashant D; Vigara, Laura; Burguete, M Isabel; Galindo, Francisco; Luis, Santiago V

2017-08-09

The fluorescence quenching, by a series of amino acids, of pseudopeptidic compounds acting as probes for cellular acidity has been investigated. It has been found that amino acids containing electron-rich aromatic side chains like Trp or Tyr, as well as Met quench the emission of the probes mainly via a collisional mechanism, with Stern-Volmer constants in the 7-43 M -1 range, while other amino acids such as His, Val or Phe did not cause deactivation of the fluorescence. Only a minor contribution of a static quenching due to the formation of ground-state complexes has been found for Trp and Tyr, with association constants in the 9-24 M -1 range. For these ground-state complexes, a comparison between the macrocyclic probes and an open chain analogue reveals the existence of a moderate macrocyclic effect due to the preorganization of the probes in the more rigid structure.

Inner-shell excitation and ionic fragmentation of molecules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hitchcock, A.P.; Tyliszczak, T.; Cavell, R.G.

1997-04-01

Inner-shell excitation and associated decay spectroscopies are site specific probes of electronic and geometrical structure and photoionization dynamics. X-ray absorption probes the geometric and electronic structure, while time-of-flight mass spectrometry with multi-coincidence detection provides information on the photofragmentation dynamics of the initially produced inner-shell state. Auger decay of inner-shell excited and ionised states is an efficient source of multiply charged ions. The charge separation and fragmentation of these species, studied by photoelectron-photoion-photoion coincidence (also called charge separation mass spectrometry) gives insights into bonding and electronic structure. In molecules, the dependence of the fragmentation process on the X-ray energy can revealmore » cases of site and/or state selective fragmentation. At the ALS the authors have examined the soft X-ray spectroscopy and ionic fragmentation of a number of molecules, including carboranes, silylenes, phosphorus halides, SF{sub 6} and CO{sub 2}. Their work is illustrated using results from the carborane and PF{sub 3} studies.« less

Small signal analysis of four-wave mixing in InAs/GaAs quantum-dot semiconductor optical amplifiers

NASA Astrophysics Data System (ADS)

Ma, Shaozhen; Chen, Zhe; Dutta, Niloy K.

2009-02-01

A model to study four-wave mixing (FWM) wavelength conversion in InAs-GaAs quantum-dot semiconductor optical amplifier is proposed. Rate equations involving two QD states are solved to simulate the carrier density modulation in the system, results show that the existence of QD excited state contributes to the ultra fast recover time for single pulse response by serving as a carrier reservoir for the QD ground state, its speed limitations are also studied. Nondegenerate four-wave mixing process with small intensity modulation probe signal injected is simulated using this model, a set of coupled wave equations describing the evolution of all frequency components in the active region of QD-SOA are derived and solved numerically. Results show that better FWM conversion efficiency can be obtained compared with the regular bulk SOA, and the four-wave mixing bandwidth can exceed 1.5 THz when the detuning between pump and probe lights is 0.5 nm.

Caspase-Activated Cell-Penetrating Peptides Reveal Temporal Coupling Between Endosomal Release and Apoptosis in an RGC-5 Cell Model

PubMed Central

Johnson, James R.; Kocher, Brandon; Barnett, Edward M.; Marasa, Jayne; Piwnica-Worms, David

2012-01-01

Caspase-activatable cell-penetrating peptide (CPP) probes, designed for efficient cell uptake and specificity via cleavable intramolecular quenched-fluorophore strategies, show promise for identifying and imaging retinal ganglion cell apoptosis in vivo. However, initial cell uptake and trafficking events cannot be visualized because the probes are designed to be optically quenched in the intact state. To visualize subcellular activation events in real-time during apoptosis, a new series of matched quenched and non-quenched CPP probes were synthesized. In both native and staurosporine-differentiated RGC-5 cells, probe uptake was time- and concentration-dependent through clathrine-, caveolin- and pinocytosis-mediated endocytic mechanisms. During apoptosis, KcapTR488, a novel dual fluorophore CPP probe, revealed by multi-spectral imaging a temporal coupling of endosomal release and effector caspase activation in RGC-5 cells. The novel CPPs described herein provide new tools to study spatial and temporal regulation of endosomal permeability during apoptosis. PMID:22900707

Experimental validation of an 8 element EMAT phased array probe for longitudinal wave generation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Le Bourdais, Florian, E-mail: florian.lebourdais@cea.fr; Marchand, Benoit, E-mail: florian.lebourdais@cea.fr

2015-03-31

Sodium cooled Fast Reactors (SFR) use liquid sodium as a coolant. Liquid sodium being opaque, optical techniques cannot be applied to reactor vessel inspection. This makes it necessary to develop alternative ways of assessing the state of the structures immersed in the medium. Ultrasonic pressure waves are well suited for inspection tasks in this environment, especially using pulsed electromagnetic acoustic transducers (EMAT) that generate the ultrasound directly in the liquid sodium. The work carried out at CEA LIST is aimed at developing phased array EMAT probes conditioned for reactor use. The present work focuses on the experimental validation of amore » newly manufactured 8 element probe which was designed for beam forming imaging in a liquid sodium environment. A parametric study is carried out to determine the optimal setup of the magnetic assembly used in this probe. First laboratory tests on an aluminium block show that the probe has the required beam steering capabilities.« less

Probing disk wind and other properties of 4U 1630-47

NASA Astrophysics Data System (ADS)

Bhattacharyya, Sudip

2015-09-01

The accreting Galactic black hole transient 4U 1630-47, which is currently in outburst, is an ideal source to probe two types of accreted matter ejection: (1) via disk wind and (2) via jet, both using the observed narrow spectral lines (Diaz Trigo et al., 2013, Nature, 504, 206; Neilsen et al. 2014; Diaz Trigo et al. 2014). Chandra gratings are ideal to study such lines. The source also showed indications of high-frequency (HF) quasi-periodic oscillations (QPOs) in a rather high (150-450 Hz) frequency range, which can be extremely useful to probe the strong gravity regime. The AstroSat satellite, because of its large area and high timing resolution in a broad energy band, can potentially detect and measure HF QPOs and probe the source broadband spectrum and state. Hence, our proposed 30 ks Chandra exposure, nearly contemporaneous with complementary AstroSat observations, will provide an excellent way to probe the accretion and ejection mechanism in the strong gravity regime.

Two-Color Pump-Probe Measurement of Photonic Quantum Correlations Mediated by a Single Phonon

NASA Astrophysics Data System (ADS)

Anderson, Mitchell D.; Tarrago Velez, Santiago; Seibold, Kilian; Flayac, Hugo; Savona, Vincenzo; Sangouard, Nicolas; Galland, Christophe

2018-06-01

We propose and demonstrate a versatile technique to measure the lifetime of the one-phonon Fock state using two-color pump-probe Raman scattering and spectrally resolved, time-correlated photon counting. Following pulsed laser excitation, the n =1 phonon Fock state is probabilistically prepared by projective measurement of a single Stokes photon. The detection of an anti-Stokes photon generated by a second, time-delayed laser pulse probes the phonon population with subpicosecond time resolution. We observe strongly nonclassical Stokes-anti-Stokes correlations, whose decay maps the single phonon dynamics. Our scheme can be applied to any Raman-active vibrational mode. It can be modified to measure the lifetime of n ≥1 Fock states or the phonon quantum coherences through the preparation and detection of two-mode entangled vibrational states.

Two-Color Pump-Probe Measurement of Photonic Quantum Correlations Mediated by a Single Phonon.

PubMed

Anderson, Mitchell D; Tarrago Velez, Santiago; Seibold, Kilian; Flayac, Hugo; Savona, Vincenzo; Sangouard, Nicolas; Galland, Christophe

2018-06-08

We propose and demonstrate a versatile technique to measure the lifetime of the one-phonon Fock state using two-color pump-probe Raman scattering and spectrally resolved, time-correlated photon counting. Following pulsed laser excitation, the n=1 phonon Fock state is probabilistically prepared by projective measurement of a single Stokes photon. The detection of an anti-Stokes photon generated by a second, time-delayed laser pulse probes the phonon population with subpicosecond time resolution. We observe strongly nonclassical Stokes-anti-Stokes correlations, whose decay maps the single phonon dynamics. Our scheme can be applied to any Raman-active vibrational mode. It can be modified to measure the lifetime of n≥1 Fock states or the phonon quantum coherences through the preparation and detection of two-mode entangled vibrational states.

Cavity QED with hybrid nanocircuits: from atomic-like physics to condensed matter phenomena

NASA Astrophysics Data System (ADS)

Cottet, Audrey; Dartiailh, Matthieu C.; Desjardins, Matthieu M.; Cubaynes, Tino; Contamin, Lauriane C.; Delbecq, Matthieu; Viennot, Jérémie J.; Bruhat, Laure E.; Douçot, Benoit; Kontos, Takis

2017-11-01

Circuit QED techniques have been instrumental in manipulating and probing with exquisite sensitivity the quantum state of superconducting quantum bits coupled to microwave cavities. Recently, it has become possible to fabricate new devices in which the superconducting quantum bits are replaced by hybrid mesoscopic circuits combining nanoconductors and metallic reservoirs. This mesoscopic QED provides a new experimental playground to study the light-matter interaction in electronic circuits. Here, we present the experimental state of the art of mesoscopic QED and its theoretical description. A first class of experiments focuses on the artificial atom limit, where some quasiparticles are trapped in nanocircuit bound states. In this limit, the circuit QED techniques can be used to manipulate and probe electronic degrees of freedom such as confined charges, spins, or Andreev pairs. A second class of experiments uses cavity photons to reveal the dynamics of electron tunneling between a nanoconductor and fermionic reservoirs. For instance, the Kondo effect, the charge relaxation caused by grounded metallic contacts, and the photo-emission caused by voltage-biased reservoirs have been studied. The tunnel coupling between nanoconductors and fermionic reservoirs also enable one to obtain split Cooper pairs, or Majorana bound states. Cavity photons represent a qualitatively new tool to study these exotic condensed matter states.

Cavity QED with hybrid nanocircuits: from atomic-like physics to condensed matter phenomena.

PubMed

Cottet, Audrey; Dartiailh, Matthieu C; Desjardins, Matthieu M; Cubaynes, Tino; Contamin, Lauriane C; Delbecq, Matthieu; Viennot, Jérémie J; Bruhat, Laure E; Douçot, Benoit; Kontos, Takis

2017-11-01

Circuit QED techniques have been instrumental in manipulating and probing with exquisite sensitivity the quantum state of superconducting quantum bits coupled to microwave cavities. Recently, it has become possible to fabricate new devices in which the superconducting quantum bits are replaced by hybrid mesoscopic circuits combining nanoconductors and metallic reservoirs. This mesoscopic QED provides a new experimental playground to study the light-matter interaction in electronic circuits. Here, we present the experimental state of the art of mesoscopic QED and its theoretical description. A first class of experiments focuses on the artificial atom limit, where some quasiparticles are trapped in nanocircuit bound states. In this limit, the circuit QED techniques can be used to manipulate and probe electronic degrees of freedom such as confined charges, spins, or Andreev pairs. A second class of experiments uses cavity photons to reveal the dynamics of electron tunneling between a nanoconductor and fermionic reservoirs. For instance, the Kondo effect, the charge relaxation caused by grounded metallic contacts, and the photo-emission caused by voltage-biased reservoirs have been studied. The tunnel coupling between nanoconductors and fermionic reservoirs also enable one to obtain split Cooper pairs, or Majorana bound states. Cavity photons represent a qualitatively new tool to study these exotic condensed matter states.

Ultrafast multi-pulse transient absorption spectroscopy of fucoxanthin chlorophyll a protein from Phaeodactylum tricornutum.

PubMed

West, Robert G; Bína, David; Fuciman, Marcel; Kuznetsova, Valentyna; Litvín, Radek; Polívka, Tomáš

2018-05-01

We have applied femtosecond transient absorption spectroscopy in pump-probe and pump-dump-probe regimes to study energy transfer between fucoxanthin and Chl a in fucoxanthin-Chl a complex from the pennate diatom Phaeodactylum tricornutum. Experiments were carried out at room temperature and 77 K to reveal temperature dependence of energy transfer. At both temperatures, the ultrafast (<100 fs) energy transfer channel from the fucoxanthin S 2 state is active and is complemented by the second pathway via the combined S 1 /ICT state. The S 1 /ICT-Chl a pathway has two channels, the fast one characterized by sub-picosecond energy transfer, and slow having time constants of 4.5 ps at room temperature and 6.6 ps at 77 K. The overall energy transfer via the S 1 /ICT is faster at 77 K, because the fast component gains amplitude upon lowering the temperature. The pump-dump-probe regime, with the dump pulse centered in the spectral region of ICT stimulated emission at 950 nm and applied at 2 ps after excitation, proved that the S 1 and ICT states of fucoxanthin in FCP are individual, yet coupled entities. Analysis of the pump-dump-probe data suggested that the main energy donor in the slow S 1 /ICT-Chl a route is the S 1 part of the S 1 /ICT potential surface. Copyright © 2018 Elsevier B.V. All rights reserved.

Micromanipulation and physiological monitoring of cells using two-photon excited fluorescence in cw laser tweezers

NASA Astrophysics Data System (ADS)

Sonek, Gregory J.; Liu, Yagang; Berns, Michael W.; Tromberg, Bruce J.

1996-05-01

We report the observation of two-photon fluorescence excitation and cell confinement, simultaneously, in a continuous-wave (cw) single-beam gradient force optical trap, and demonstrate its use as an in-situ probe to study the physiological state of an optically confined cell sample. At the wavelength of 1064 nm, a single focused gaussian laser beam is used to simultaneously confine, and excite visible fluorescence from, a human sperm cell that has been tagged with propidium iodide, a exogenous fluorescent dye that functions as a viability assay of cellular physiological state. The intensity at the dye peak emission wavelength of 620 nm exhibits a near-square-law dependence on incident trapping beam photon laser power, a behavior consistent with a two-photon absorption process. In addition, for a sperm cell held stationary in the optical tweezers for a period of several minutes at a constant trapping power, red fluorescence emission was observed to increase the time, indicating that the cell has gradually transitioned between a live and dead state. Two-photon excited fluorescence was also observed in chinese hamster ovary cells that were confined by cw laser tweezers and stained with either propidium iodide or Snarf, a pH-sensitive dye probe. These results suggest that, for samples suitably tagged with fluorescent probes and vital stains, optical tweezers can be used to generate their own in-situ diagnostic optical probes of cellular viability or induced photodamage, via two-photon processes.

Overtone spectroscopy of N2H+ molecular ions—application of cavity ring-down spectroscopy

NASA Astrophysics Data System (ADS)

Kálosi, Á.; Dohnal, P.; Shapko, D.; Roučka, Š.; Plašil, R.; Johnsen, R.; Glosík, J.

2017-10-01

A stationary afterglow apparatus in conjunction with a laser absorption cavity ring-down spectrometer has been employed to observe absorption lines in the P- and R-branches of the (200) <-- (000) and (2110) <-- (0110) vibrational bands of the N2H+ molecular ion as a part of an ongoing study of the electron-ion recombination of N2H+ in afterglow plasmas. The probed absorption lines lie in the near-infrared spectral region around 1580 nm. The observed transition wavenumbers were fitted to experimental accuracy and improved molecular constants for the (200) vibrational state were obtained. The employed experimental technique enables probing of the translational, rotational and vibrational temperature of the studied ions as well as the determination of the number densities of different quantum states of the ion in discharge and afterglow plasma.

Quantum Discord Determines the Interferometric Power of Quantum States

NASA Astrophysics Data System (ADS)

Girolami, Davide; Souza, Alexandre M.; Giovannetti, Vittorio; Tufarelli, Tommaso; Filgueiras, Jefferson G.; Sarthour, Roberto S.; Soares-Pinto, Diogo O.; Oliveira, Ivan S.; Adesso, Gerardo

2014-05-01

Quantum metrology exploits quantum mechanical laws to improve the precision in estimating technologically relevant parameters such as phase, frequency, or magnetic fields. Probe states are usually tailored to the particular dynamics whose parameters are being estimated. Here we consider a novel framework where quantum estimation is performed in an interferometric configuration, using bipartite probe states prepared when only the spectrum of the generating Hamiltonian is known. We introduce a figure of merit for the scheme, given by the worst-case precision over all suitable Hamiltonians, and prove that it amounts exactly to a computable measure of discord-type quantum correlations for the input probe. We complement our theoretical results with a metrology experiment, realized in a highly controllable room-temperature nuclear magnetic resonance setup, which provides a proof-of-concept demonstration for the usefulness of discord in sensing applications. Discordant probes are shown to guarantee a nonzero phase sensitivity for all the chosen generating Hamiltonians, while classically correlated probes are unable to accomplish the estimation in a worst-case setting. This work establishes a rigorous and direct operational interpretation for general quantum correlations, shedding light on their potential for quantum technology.

Quantum Nuclear Dynamics Pumped and Probed by Ultrafast Polarization Controlled Steering of a Coherent Electronic State in LiH.

PubMed

Nikodem, Astrid; Levine, R D; Remacle, F

2016-05-19

The quantum wave packet dynamics following a coherent electronic excitation of LiH by an ultrashort, polarized, strong one-cycle infrared optical pulse is computed on several electronic states using a grid method. The coupling to the strong field of the pump and the probe pulses is included in the Hamiltonian used to solve the time-dependent Schrodinger equation. The polarization of the pump pulse allows us to control the localization in time and in space of the nonequilibrium coherent electronic motion and the subsequent nuclear dynamics. We show that transient absorption, resulting from the interaction of the total molecular dipole with the electric fields of the pump and the probe, is a very versatile probe of the different time scales of the vibronic dynamics. It allows probing both the ultrashort, femtosecond time scale of the electronic coherences as well as the longer dozens of femtoseconds time scales of the nuclear motion on the excited electronic states. The ultrafast beatings of the electronic coherences in space and in time are shown to be modulated by the different periods of the nuclear motion.

Near infrared lasers in flow cytometry.

PubMed

Telford, William G

2015-07-01

Technology development in flow cytometry has closely tracked laser technology, the light source that flow cytometers almost exclusively use to excite fluorescent probes. The original flow cytometers from the 1970s and 1980s used large water-cooled lasers to produce only one or two laser lines at a time. Modern cytometers can take advantage of the revolution in solid state laser technology to use almost any laser wavelength ranging from the ultraviolet to the near infrared. Commercial cytometers can now be equipped with many small solid state lasers, providing almost any wavelength needed for cellular analysis. Flow cytometers are now equipped to analyze 20 or more fluorescent probes simultaneously, requiring multiple laser wavelengths. Instrument developers are now trying to increase this number by designing fluorescent probes that can be excited by laser wavelength at the "edges" of the visible light range, in the near ultraviolet and near-infrared region. A variety of fluorescent probes have been developed that excite with violet and long wavelength ultraviolet light; however, the near-infrared range (660-800 nm) has yet seen only exploitation in flow cytometry. Fortunately, near-infrared laser diodes and other solid state laser technologies appropriate for flow cytometry have been in existence for some time, and can be readily incorporated into flow cytometers to accelerate fluorescent probe development. The near infrared region represents one of the last "frontiers" to maximize the number of fluorescent probes that can be analyzed by flow cytometry. In addition, near infrared fluorescent probes used in biomedical tracking and imaging could also be employed for flow cytometry with the correct laser wavelengths. This review describes the available technology, including lasers, fluorescent probes and detector technology optimal for near infrared signal detection. Published by Elsevier Inc.

In vivo determination of steric and electrostatic exclusion of albumin in rat skin and skeletal muscle

PubMed Central

Gyenge, Christina C; Tenstad, Olav; Wiig, Helge

2003-01-01

In order to estimate the magnitude of electrostatic exclusion provided by the fixed negative charges of the skin and muscle interstitia of rat in vivo we measured the distribution volumes of two differently charged albumin probes within these tissues. An implanted osmotic pump was used to reach and maintain a steady-state extracellular concentration of a mixture containing two iodine-labelled probes: a charged-modified human serum albumin, cHSA (i.e. a positive probe, isoelectirc point (pI) = 7.6) and a native human serum albumin, HSA (i.e. a normally charged, negative probe, pI = 5.0). Steady-state tissue concentrations were achieved after intravenous infusion of probes for 5–7 days. At the end of this period the animals were nephrectomized and a bolus of 51Cr-EDTA was administered for estimating the extracellular volume. Plasma volumes were measured as 5-min distribution volume of 125I-HSA in separate experiments. The steady-state interstitial fluid concentrations of all probes were determined using nylon wicks implanted postmortem. Calculations of labelled probes were made for interstitial fluid volumes (Vi), extravascular albumin distribution volumes (Vav,a) and relative interstitial excluded volume fractions (Vex,a/Vi). We found that the positive probe is excluded from a significantly smaller fraction of the interstitium. Specifically, the average relative albumin exclusion fractions obtained were: 16% and 26% in skeletal muscle and 30% and 40% in skin, for cHSA and HSA, respectively. On average, the fixed negative charges of the interstitium are responsible for about 40% of the total albumin exclusion in skeletal muscle and 25% in the whole skin tissue and thus, contribute significantly to volume exclusion in these tissues. PMID:12937287

In vivo determination of steric and electrostatic exclusion of albumin in rat skin and skeletal muscle.

PubMed

Gyenge, Christina C; Tenstad, Olav; Wiig, Helge

2003-11-01

In order to estimate the magnitude of electrostatic exclusion provided by the fixed negative charges of the skin and muscle interstitia of rat in vivo we measured the distribution volumes of two differently charged albumin probes within these tissues. An implanted osmotic pump was used to reach and maintain a steady-state extracellular concentration of a mixture containing two iodine-labelled probes: a charged-modified human serum albumin, cHSA (i.e. a positive probe, isoelectirc point (pI) = 7.6) and a native human serum albumin, HSA (i.e. a normally charged, negative probe, pI = 5.0). Steady-state tissue concentrations were achieved after intravenous infusion of probes for 5-7 days. At the end of this period the animals were nephrectomized and a bolus of 51Cr-EDTA was administered for estimating the extracellular volume. Plasma volumes were measured as 5-min distribution volume of 125I-HSA in separate experiments. The steady-state interstitial fluid concentrations of all probes were determined using nylon wicks implanted postmortem. Calculations of labelled probes were made for interstitial fluid volumes (Vi), extravascular albumin distribution volumes (Vav,a) and relative interstitial excluded volume fractions (Vex,a/Vi). We found that the positive probe is excluded from a significantly smaller fraction of the interstitium. Specifically, the average relative albumin exclusion fractions obtained were: 16% and 26% in skeletal muscle and 30% and 40% in skin, for cHSA and HSA, respectively. On average, the fixed negative charges of the interstitium are responsible for about 40% of the total albumin exclusion in skeletal muscle and 25% in the whole skin tissue and thus, contribute significantly to volume exclusion in these tissues.

Study of Solid-State Diffusion of Bi in Polycrystalline Sn Using Electron Probe Microanalysis

NASA Astrophysics Data System (ADS)

Delhaise, André M.; Perovic, Doug D.

2018-03-01

Current lead-free solders such as SAC305 exhibit degradation in microstructure, properties, and reliability. Current third-generation alloys containing bismuth (Bi) demonstrate preservation of strength after aging; this is accompanied by homogenization of the Bi precipitates in the tin (Sn) matrix, driven via solid-state diffusion. This study quantifies the diffusion of Bi in Sn. Diffusion couples were prepared by mating together polished samples of pure Sn and Bi. Couples were annealed at one of three temperatures, viz. 85°C for 7 days, 100°C for 2 days, or 125°C for 1 day. After cross-sectioning the couples to examine the diffusion microstructure and grain size, elemental analysis was performed using electron probe microanalysis. For this study, it was assumed that the diffusivity of Bi in Sn is concentration dependent, therefore inverse methods were used to solve Fick's non-steady-state diffusion equation. In addition, Darken analysis was used to extract the impurity diffusivity of Bi in Sn at each temperature, allowing estimation of the Arrhenius parameters D 0 and k A.

Probing and Manipulating Ultracold Fermi Superfluids

NASA Astrophysics Data System (ADS)

Jiang, Lei

Ultracold Fermi gas is an exciting field benefiting from atomic physics, optical physics and condensed matter physics. It covers many aspects of quantum mechanics. Here I introduce some of my work during my graduate study. We proposed an optical spectroscopic method based on electromagnetically-induced transparency (EIT) as a generic probing tool that provides valuable insights into the nature of Fermi paring in ultracold Fermi gases of two hyperfine states. This technique has the capability of allowing spectroscopic response to be determined in a nearly non-destructive manner and the whole spectrum may be obtained by scanning the probe laser frequency faster than the lifetime of the sample without re-preparing the atomic sample repeatedly. Both quasiparticle picture and pseudogap picture are constructed to facilitate the physical explanation of the pairing signature in the EIT spectra. Motivated by the prospect of realizing a Fermi gas of 40K atoms with a synthetic non-Abelian gauge field, we investigated theoretically BEC-HCS crossover physics in the presence of a Rashba spin-orbit coupling in a system of two-component Fermi gas with and without a Zeeman field that breaks the population balance. A new bound state (Rashba pair) emerges because of the spin-orbit interaction. We studied the properties of Rashba pairs using a standard pair fluctuation theory. As the two-fold spin degeneracy is lifted by spin-orbit interaction, bound pairs with mixed singlet and triplet pairings (referred to as rashbons) emerge, leading to an anisotropic superfluid. We discussed in detail the experimental signatures for observing the condensation of Rashba pairs by calculating various physical observables which characterize the properties of the system and can be measured in experiment. The role of impurities as experimental probes in the detection of quantum material properties is well appreciated. Here we studied the effect of a single classical impurity in trapped ultracold Fermi superfluids. Although a non-magnetic impurity does not change macroscopic properties of s-wave Fermi superfluids, depending on its shape and strength, a magnetic impurity can induce single or multiple mid-gap bound states. The multiple mid-gap states could coincide with the development of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase within the superfluid. As an analog of the Scanning Tunneling Microscope, we proposed a modified radio frequency spectroscopic method to measure the focal density of states which can be employed to detect these states and other quantum phases of cold atoms. A key result of our self consistent Bogoliubov-de Gennes calculations is that a magnetic impurity can controllably induce an FFLO state at currently accessible experimental parameters.

Design, Validation, and Testing of a Hot-Film Anemometer for Hypersonic Flow

NASA Astrophysics Data System (ADS)

Sheplak, Mark

The application of constant-temperature hot-film anemometry to hypersonic flow has been reviewed and extended in this thesis. The objective of this investigation was to develop a measurement tool capable of yielding continuous, high-bandwidth, quantitative, normal mass-flux and total -temperature measurements in moderate-enthalpy environments. This research has produced a probe design that represents a significant advancement over existing designs, offering the following improvements: (1) a five-fold increase in bandwidth; (2) true stagnation-line sensor placement; (3) a two order-of-magnitude decrease in sensor volume; and (4) over a 70% increase in maximum film temperature. These improvements were achieved through substrate design, sensor placement, the use of high-temperature materials, and state -of-the-art microphotolithographic fabrication techniques. The experimental study to characterize the probe was performed in four different hypersonic wind tunnels at NASA-Langley Research Center. The initial test consisted of traversing the hot film through a Mach 6, flat-plate, turbulent boundary layer in air. The detailed static-calibration measurements that followed were performed in two different hypersonic flows: a Mach 11 helium flow and Mach 6 air flow. The final test of this thesis consisted of traversing the probe through the Mach 6 wake of a 70^ circ blunt body. The goal of this test was to determine the state (i.e., laminar or turbulent) of the wake. These studies indicate that substrate conduction effects result in instrumentation characteristics that prevent the hot-film anemometer from being used as a quantitative tool. The extension of this technique to providing quantitative information is dependent upon the development of lower thermal-conductivity substrate materials. However, the probe durability, absence of strain gauging, and high bandwidth represent significant improvements over the hot-wire technique for making qualitative measurements. Potential uses for this probe are: frequency identification for resonant flows, transition studies, turbulence detection for quiet-tunnel development and reattaching turbulent shear flows, and qualitative turbulence studies of shock-wave/turbulent boundary layer interactions.

Fluorescence molecular probes for sensitive point detection of amyloid fibrils and protofibrils

NASA Astrophysics Data System (ADS)

Lindgren, Mikael; Jonsson, Per; Sörgjerd, Karin; Hammarström, Per

2005-10-01

Protein based infections such as prion diseases have lately attracted a large amount of interest, primarily due to the Mad Cow Epidemic in Great Britain, and the increase of Alzheimer's disease and related diseases in the ageing Western society. Infective proteins are very stable and almost untraceable prior to infection making them ideal as biological weapons. Particularly if the used agent is of human origin, the immunoresponse can be avoided, leaving no trace of the infectious agent. The transient nature of infectious oligomeric intermediates of misfolded proteins or peptide fragments that later matures into fibrillar aggregates makes them hard to study, and methods to detect and study these species are sparse. There exist a number of fluorescent probes that bind specifically to protein amyloidic structures. Thioflavins (ThT, ThS), Congo and Nile red, 4-(dicyanovinyl)-julolidine (DCVJ), as well as derivatives amino-8-naphtalene sulphonate (ANS, Bis-ANS) which are known to bind to the fibrillar or pre-fibrillar states with dissociation constants of typically 1 - 20 μM. Here, transthyretin (TTR), insulin and lysozyme were used as model proteins to detect different amyloid precursor states for diseases such as senile systemic amyloidosis, familial amyloidotic polyneuropathy (FAP) and iatrogenic amyloidosis. Specifically, the probes were employed in static assays to characterize protofibrillar and mature amyloid fibrillar states using steady state and time-resolved fluorescence techniques. Particularly, we investigate and report on the possibility to detect protofibrillar states at low concentration levels using modern fluorescence array detector systems in conjunction with lasers operating in the blue or ultraviolett wavelengths as excitation source. Results of ANS, ThT and a ThT analogue (abbreviated ThC) are discussed.

Evolving optical second-harmonic anisotropy at the cleaved Bi2Se3 surface

NASA Astrophysics Data System (ADS)

An, Yong; Green, Avery; Diebold, Alain

Bismuth selenide (Bi2Se3) is a centrosymmetric topological insulator with conducting surface states. The surface states have been studied by various electrical and optical techniques in air, but ambience effects and surface aging have not been adequately addressed. Optical second-harmonic generation (SHG) is a suitable probe for the Bi2Se3 surface because SHG arises from symmetry breaking at the surface and thus should detect surface states preferentially over bulk states. However, a strong time dependence of SHG is often observed, hampering the detection and investigation of the surface states. Here we find a new phenomenon in which the major and minor intensity lobes of a measured rotational-anisotropy SHG pattern from a cleaved Bi2Se3 (111) surface can significantly change with time and eventually switch their amplitudes. This switching provides a means for tracking the progress of surface oxidation inside a quintuple layer of Bi2Se3. We also perform pump-probe SHG experiments, comparatively on freshly cleaved and oxidized Bi2Se3 surfaces, to study charge dynamics at the oxide/Bi2Se3 interface and to detect spin polarization of photoexcited surface states in the Bi2Se3 topological insulator. This work was supported by the SRC NRI Institute for Nanoelectronics Discovery and Exploration (INDEX).

Probing dark matter at the LHC using vector boson fusion processes.

PubMed

Delannoy, Andres G; Dutta, Bhaskar; Gurrola, Alfredo; Johns, Will; Kamon, Teruki; Luiggi, Eduardo; Melo, Andrew; Sheldon, Paul; Sinha, Kuver; Wang, Kechen; Wu, Sean

2013-08-09

Vector boson fusion processes at the Large Hadron Collider (LHC) provide a unique opportunity to search for new physics with electroweak couplings. A feasibility study for the search of supersymmetric dark matter in the final state of two vector boson fusion jets and large missing transverse energy is presented at 14 TeV. Prospects for determining the dark matter relic density are studied for the cases of wino and bino-Higgsino dark matter. The LHC could probe wino dark matter with mass up to approximately 600 GeV with a luminosity of 1000  fb(-1).

A Causal Contiguity Effect That Persists across Time Scales

ERIC Educational Resources Information Center

Kilic, Asli; Criss, Amy H.; Howard, Marc W.

2013-01-01

The contiguity effect refers to the tendency to recall an item from nearby study positions of the just recalled item. Causal models of contiguity suggest that recalled items are used as probes, causing a change in the memory state for subsequent recall attempts. Noncausal models of the contiguity effect assume the memory state is unaffected by…

A Solid-State Deuterium NMR and SFG Study of the Side Chain Dynamics of Peptides Adsorbed onto Surfaces

PubMed Central

Breen, Nicholas F.; Weidner, Tobias; Li, Kun; Castner, David G.; Drobny, Gary P.

2011-01-01

The artificial amphiphilic peptide LKα14 adopts a helical structure at interfaces, with opposite orientation of its leucine (L, hydrophobic) and lysine (K, hydrophilic) side chains. When adsorbed onto surfaces, different residue side chains necessarily have different proximities to the surface, depending on both their position in the helix and the composition of the surface itself. Deuterating the individual leucine residues (isopropyl-d7) permits the use of solid-state deuterium NMR as a site-specific probe of side chain dynamics. In conjunction with SFG as a probe of the peptide binding face, we demonstrate that the mobility of specific leucine side chains at the interface is quantifiable in terms of their surface proximity. PMID:19764755

Complex structural dynamics of nanocatalysts revealed in Operando conditions by correlated imaging and spectroscopy probes

DOE PAGES

Li, Y.; Zakharov, D.; Zhao, S.; ...

2015-06-29

Understanding how heterogeneous catalysts change size, shape and structure during chemical reactions is limited by the paucity of methods for studying catalytic ensembles in working state, that is, in operando conditions. Here by a correlated use of synchrotron X-ray absorption spectroscopy and scanning transmission electron microscopy in operando conditions, we quantitatively describe the complex structural dynamics of supported Pt catalysts exhibited during an exemplary catalytic reaction—ethylene hydrogenation. This work exploits a microfabricated catalytic reactor compatible with both probes. The results demonstrate dynamic transformations of the ensemble of Pt clusters that spans a broad size range throughout changing reaction conditions. Lastly,more » this method is generalizable to quantitative operando studies of complex systems using a wide variety of X-ray and electron-based experimental probes.« less

Hypochlorite-Mediated Modulation of Photoinduced Electron Transfer in a Phenothiazine-Boron dipyrromethene Electron Donor-Acceptor Dyad: A Highly Water Soluble "Turn-On" Fluorescent Probe for Hypochlorite.

PubMed

Soni, Disha; Duvva, Naresh; Badgurjar, Deepak; Roy, Tapta Kanchan; Nimesh, Surendra; Arya, Geeta; Giribabu, Lingamallu; Chitta, Raghu

2018-04-16

A highly water-soluble phenothiazine (PTZ)-boron dipyrromethene (BODIPY)-based electron donor-acceptor dyad (WS-Probe), which contains BODIPY as the signaling antennae and PTZ as the OCl - reactive group, was designed and used as a fluorescent chemosensor for the detection of OCl - . Upon addition of incremental amounts of NaOCl, the quenched fluorescence of WS-Probe was enhanced drastically, which indicated the inhibition of reductive photoinduced electron transfer (PET) from PTZ to 1 BODIPY*; the detection limit was calculated to be 26.7 nm. Selectivity studies with various reactive oxygen species, cations, and anions revealed that WS-Probe was able to detect OCl - selectively. Steady-state fluorescence studies performed at varied pH suggested that WS-Probe can detect NaOCl and exhibits maximum fluorescence in the pH range of 7 to 8, similar to physiological conditions. ESI-MS analysis and 1 H NMR spectroscopy titrations showed the formation of sulfoxide as the major oxidized product upon addition of hypochlorite. More interestingly, when WS-Probe was treated with real water samples, the fluorescence response was clearly visible with tap water and disinfectant, which indicated the presence of OCl - in these samples. The in vitro cell viability assay performed with human embryonic kidney 293 (HEK 293) cells suggested that WS-probe is non-toxic up to 10 μm and implicates the use of the probe for biological applications. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Spectroscopic and theoretical investigations on intramolecular charge transfer phenomenon in 1-3-dioxolane derivative

NASA Astrophysics Data System (ADS)

Zhang, Zhiyong; Zhang, Zhongzhi; Luo, Yijing; Sun, Shanshan; Zhang, Guangqing

2018-02-01

High fluorescence quantum yield (FQY) and large Stokes shift (SS) cannot be easily achieved simultaneously by traditional PICT or TICT fluorescent probe. However, an 1-3-dioxolane derivative named 5-methyl-8,9-dihydro-5H-[1,3]dioxolo[4,5-b]carbazol-6(7H)-one (MDDCO) features both high FQY and large SS. The purpose of this study is to search the mechanism behind this phenomenon by theoretical method. Simulated structure changes and charge transfer suggest ICT process in MDDCO is similar to PLICT (Planarized Intramolecular Charge Transfer) process. Calculated UV-Vis spectra and fluorescence spectra show that PLICT-like state (S1 state) of MDDCO leads to large SS. Computed transient-absorption spectra and radiative decay rates indicate that PLICT-like state is key factor for high FQY of MDDCO. These findings suggest that PLICT-like state in 1,3-dioxolane derivatives can achieve both large SS and high FQY, which presents a new method for high-performance fluorescent probe design.

Selective ultrafast probing of transient hot chemisorbed and precursor states of CO on Ru(0001).

PubMed

Beye, M; Anniyev, T; Coffee, R; Dell'Angela, M; Föhlisch, A; Gladh, J; Katayama, T; Kaya, S; Krupin, O; Møgelhøj, A; Nilsson, A; Nordlund, D; Nørskov, J K; Öberg, H; Ogasawara, H; Pettersson, L G M; Schlotter, W F; Sellberg, J A; Sorgenfrei, F; Turner, J J; Wolf, M; Wurth, W; Oström, H

2013-05-03

We have studied the femtosecond dynamics following optical laser excitation of CO adsorbed on a Ru surface by monitoring changes in the occupied and unoccupied electronic structure using ultrafast soft x-ray absorption and emission. We recently reported [M. Dell'Angela et al. Science 339, 1302 (2013)] a phonon-mediated transition into a weakly adsorbed precursor state occurring on a time scale of >2 ps prior to desorption. Here we focus on processes within the first picosecond after laser excitation and show that the metal-adsorbate coordination is initially increased due to hot-electron-driven vibrational excitations. This process is faster than, but occurs in parallel with, the transition into the precursor state. With resonant x-ray emission spectroscopy, we probe each of these states selectively and determine the respective transient populations depending on optical laser fluence. Ab initio molecular dynamics simulations of CO adsorbed on Ru(0001) were performed at 1500 and 3000 K providing insight into the desorption process.

Femtosecond pump-supercontinuum probe and transient lens spectroscopy of adonixanthin.

PubMed

Lenzer, Thomas; Schubert, Steffen; Ehlers, Florian; Lohse, Peter W; Scholz, Mirko; Oum, Kawon

2009-03-15

The ultrafast internal conversion (IC) dynamics of adonixanthin in organic solvents were studied by pump-supercontinuum probe (PSCP) and transient lens (TL) spectroscopy after photoexcitation to the S(2) state. Transient PSCP spectra in the range 344-768 nm provided the spectral evolution of the S(0)-->S(2) ground state bleach and S(1)-->S(n) excited state absorption. Time constants were tau(2) =115 and 111 fs for the S(2)-->S(1) IC and tau(1)=6.4 and 5.8 ps for the S(1)-->S(0) IC in acetone and methanol, respectively. There was only an insignificant polarity dependence of tau(1), underlining the negligible importance of intramolecular charge transfer (ICT) in the lowest-lying excited state of C(40) carotenoids with carbonyl substitution on the beta-ionone ring. A blueshift and a spectral narrowing of the S(1)-->S(n) ESA band, likely due to solvation dynamics, and formation of the adonixanthin radial cation at high pump energies via resonant two-photon ionization were found.

Indirect consequences of exciplex states on the phosphorescence lifetime of phenazine-based 1,2,3-triazole luminescent probes.

PubMed

Costa, Bárbara B A; Jardim, Guilherme A M; Santos, Paloma L; Calado, Hállen D R; Monkman, Andrew P; Dias, Fernando B; da Silva Júnior, Eufrânio N; Cury, Luiz A

2017-02-01

The optical properties of phenazine derivative probe solutions involving intersystem crossing from singlet to triplet states were investigated by time resolved spectroscopy. The room temperature phosphorescence emission presented different time responses when Cd 2+ ions were bound to the probe chemical structure. The complex exciplex formation observed to occur in this case was not directly responsible for the change in the phosphorescence lifetime. This was more influenced by the new molecular conformation and modified spin-orbit coupling imposed by the binding of the Cd 2+ ions to the phenazine molecules.

Vehicle Charging on the 29.036 and 29.037 Rockets of the EQUIS II Campaign.

NASA Astrophysics Data System (ADS)

Barjatya, A.; Swenson, C.; Fish, C.; Hummel, A.; Hysell, D.

2004-12-01

The rocket investigation "Scattering Layer in the Bottomside Equatorial F-region Ionosphere", was part of the NASA EQUIS II campaign. Two salvos of sounding rockets were launched from Roi Namur in Kwajalein on August 7th and 15th of 2004. The project's mission was to investigate the thin scattering layers in the post sunset equatorial F region ionosphere that act as precursors to a fully developed equatorial spread F. Each of the salvos consisted of one instrumented and two chemical release payloads. The instrumented rockets were launched westward into equatorial spread F precursor that was first observed from ground using the Altair radar. The instrumented rockets reached an apogee of ~450 km. The instruments consisted of a Sweeping Langmuir Probe (SLP), a fixed bias DC Probe (DCP), a Plasma Impedance Probe consisting of a Plasma Frequency Probe and a Plasma Sweeping Probe built at Utah State University. The instrument suite also included an Electric Field Probe built by Penn State University. This poster presents observations of vehicle charging and preliminary data from the SLP and DCP.

Cd in SnO: Probing structural effects on the electronic structure of doped oxide semiconductors through the electric field gradient at the Cd nucleus

NASA Astrophysics Data System (ADS)

Errico, Leonardo A.; Rentería, Mario; Petrilli, Helena M.

2007-04-01

We perform an ab initio study of the electric field gradient (EFG) at the nucleus of Cd impurities at substitutional Sn sites in crystalline SnO. The full-potential linearized-augmented plane wave and the projector augmented wave methods used here allow us to treat the electronic structure of the doped system and the atomic relaxations introduced by the impurities in the host in a fully self-consistent way using a supercell approach in a state-of-the-art way. Effects of the impurity charge state on the electronic and structural properties are also discussed. Since the EFG is a very subtle quantity, its determination is very useful to probe ground-state properties such as the charge density. We show that the EFG is very sensitive to structural relaxations induced by the impurity. Our theoretical predictions are compared with available experimental results.

Investigation of Systematic Effects in Atmospheric Microthermal Probe Data.

DTIC Science & Technology

1992-12-01

MICROTHERMAL PROBE DATA by Daniel S. Roper December, 1992 Thesis Advisor. Donald L. Walters Approved for public release; distribution is unlimited 93...EFFWS IN ATMOSP RIC MICROTHERMAL PROBE DATA 12. PERSONALAUTHOR(S) Da s. Roper 13s. TYPE OF REPORT 13b. TIME COVERED 14. DATE OF REPORT (year, moith, day...distribution is unlimited. Investigation of Systematic Effects in Atmospheric Microthermal Probe Data by Daniel S. Roper Captain, United States Army B.S

Energetics of subdomain movements and fluorescence probe solvation environment change in ATP-bound myosin.

PubMed

Harris, Michael J; Woo, Hyung-June

2008-11-01

Energetics of conformational changes experienced by an ATP-bound myosin head detached from actin was studied by all-atom explicit water umbrella sampling simulations. The statistics of coupling between large scale domain movements and smaller scale structural features were examined, including the closing of the ATP binding pocket, and a number of key hydrogen bond formations shown to play roles in structural and biochemical studies. The statistics for the ATP binding pocket open/close transition show an evolution of the relative stability from the open state in the early stages of the recovery stroke to the stable closed state after the stroke. The change in solvation environment of the fluorescence probe Trp507 (scallop numbering; 501 in Dictyostelium discoideum) indicates that the probe faithfully reflects the closing of the binding pocket as previously shown in experimental studies, while being directly coupled to roughly the early half of the overall large scale conformational change of the converter domain rotation. The free energy change of this solvation environment change, in particular, is -1.3 kcal/mol, in close agreement with experimental estimates. In addition, our results provide direct molecular level data allowing for interpretations of the fluorescence experiments of myosin conformational change in terms of the de-solvation of Trp side chain.

Electromagnetically induced transparency and Autler-Townes splitting in superconducting flux quantum circuits

NASA Astrophysics Data System (ADS)

Sun, Hui-Chen; Liu, Yu-xi; Ian, Hou; You, J. Q.; Il'ichev, E.; Nori, Franco

2014-06-01

We study the microwave absorption of a driven three-level quantum system, which is realized by a superconducting flux quantum circuit (SFQC), with a magnetic driving field applied to the two upper levels. The interaction between the three-level system and its environment is studied within the Born-Markov approximation, and we take into account the effects of the driving field on the damping rates of the three-level system. We study the linear response of the driven three-level SFQC to a weak probe field. The linear magnetic susceptibility of the SFQC can be changed by both the driving field and the bias magnetic flux. When the bias magnetic flux is at the optimal point, the transition from the ground state to the second-excited state is forbidden and the three-level SFQC has a ladder-type transition. Thus, the SFQC responds to the probe field like natural atoms with ladder-type transitions. However, when the bias magnetic flux deviates from the optimal point, the three-level SFQC has a cyclic transition, thus it responds to the probe field like a combination of natural atoms with ladder-type transitions and natural atoms with Λ-type transitions. In particular, we provide detailed discussions on the conditions for realizing electromagnetically induced transparency and Autler-Townes splitting in three-level SFQCs.

Preparation and Preliminary Characterization of Crystallizing Fluorescent Derivatives of Chicken Egg White Lysozyme

NASA Technical Reports Server (NTRS)

Sumida, John; Forsythe, Elizabeth L.; Pusey, Marc L.; Whitaker, Ann F. (Technical Monitor)

2001-01-01

Fluorescence is one of the most versatile and powerful tools for the study of macromolecules. While most proteins are intrinsically fluorescent, working at crystallization concentrations require the use of covalently prepared derivatives added as tracers. This approach requires derivatives that do not markedly affect the crystal packing. We have prepared fluorescent derivatives of chicken egg white lysozyme with probes bound to one of two different sites on the protein molecule. Lucifer yellow and 5-(2-aminoethyl)aminonapthalene-1-sulfonic acid (EDANS) have been attached to the side chain carboxyl of Asp(sup 101) using a carbodiimide coupling procedure. Asp(sup 101) lies within the active site cleft, and it is believed that the probes are "buried" within that cleft. Lucifer yellow and MANS probes with iodoacetamide reactive groups have been bound to His(sup 15), located on the "back side" of the molecule relative to the active site. All the derivatives fluoresce in the solution and the crystalline states. Fluorescence characterization has focused on determination of binding effects on the probe quantum yield, lifetime, absorption and emission spectra, and quenching by added solutes. Quenching studies show that, as postulated, the Asp(sup 101)-bound probes are partially sheltered from the bulk solution by their location within the active site cleft. Probes bound to His(sup 15) have quenching constants about equal to those for the free probes, indicating that this site is highly exposed to the bulk solution.

Preparation and Preliminary Characterization of Crystallizing Fluorescent Derivatives of Chicken Egg White Lysozyme

NASA Technical Reports Server (NTRS)

Sumida, John P.; Forsythe, Elizabeth L.; Pusey, Marc L.

2001-01-01

Fluorescence is one of the most versatile and powerful tools for the study of macromolecules. While most proteins are intrinsically fluorescent, working at crystallization concentrations require the use of covalently prepared derivatives added as tracers. This approach requires derivatives that do not markedly affect the crystal packing. We have prepared fluorescent derivatives of chicken egg white lysozyme with probes bound to one of two different sites on the protein molecule. Lucifer yellow and 5-(2-aminoethyl)aminonapthalene-i-sulfonic acid (EDANS) have been attached to the side chain carboxyl of Asp(sup 101) using a carbodiimide coupling procedure. Asp(sup 101) lies within the active site cleft, and it is believed that the probes are 'buried' within that cleft. Lucifer yellow and MANS probes with iodoacetamide reactive five groups have been bound to His(sup 15), located on the 'back side' of the molecule relative to the active site. All the derivatives fluoresce in the solution and the crystalline states. Fluorescence characterization has focused on determination of binding effects on the probe quantum yield, lifetime, absorption and emission spectra, and quenching by added solutes. Quenching studies show that, as postulated, the Asp(sup 101)-bound probes are partially sheltered from the bulk solution by their location within the active site cleft. Probes bound to His(sup 15) have quenching constants about equal to those for the free probes, indicating that this site is highly exposed to the bulk solution.

Pump-probe microscopy of respiratory chain pigments: towards non-fluorescent label-free metabolic imaging

NASA Astrophysics Data System (ADS)

Domingue, Scott R.; Chicco, Adam J.; Bartels, Randy A.; Wilson, Jesse W.

2017-02-01

Current label-free metabolic microscopy techniques are limited to obtaining contrast from fluorescent molecules NAD(P)H and FAD+, and are unable to determine redox state along the mitochondrial respiratory chain itself. The respiratory chain electron carriers do not fluoresce, but some are heme proteins that have redox-dependent absorption spectra. The most prominent of these, cytochrome c, has been extensively characterized by transient absorption spectroscopy, which suggests that pump-probe measurements in the vicinity of 450 - 600 nm can provide strong contrast between its redox states. Motivated by the success of pump-probe microscopy targeting another heme protein, hemoglobin, we seek to extend the technique to the cytochromes, with the ultimate goal of dissecting respiratory chain function of individual cells in live tissue. To that end, we have developed a new optical system producing ultrafast, visible, independently-tunable pulse pairs via sum-frequency generation of nonlinearly broadened pulses in periodically-poled lithium niobate. The system is pumped by a homebuilt fiber-based oscillator/amplifier emitting 1060 nm pulses at 1.3 W (63 MHz repetition rate), and produces tunable pulses in the vicinity of 488 and 532 nm. Pump-probe spectroscopy of cytochrome c with this source reveals differences in excited-state absorption relaxation times between redox states. Though redox contrast is weak with this setup, we argue that this can be improved with a resonant galvo-scanning microscope. Moreover, pump-probe images were acquired of brown adipose tissue (which contains dense mitochondria), demonstrating label-free contrast from excited-state absorption in respiratory chain hemes.

Analysis and Optimization of the Recovered ESA Huygens Mission

NASA Astrophysics Data System (ADS)

Kazeminejad, Bobby

2002-06-01

The Huygens Probe is the ESA-provided element of the joint NASA/ESA Cassini - Huygens mission to Saturn and Titan. A recently discovered design flaw in the Huygens radio receiver onboard Cassini led to a significantly different mission geometry, redesigned and implemented by both the ESA Huygens and NASA Cassini project teams. A numerical integration of the Orbiter trajectory and the Huygens descent profile with simplified assumptions for Probe attitude and correlated aerodynamic aspects offered the opportunity to re-calculate key mission parameters, which depend on the relative geometry and motion of the bodies. This was a crucial step to assess whether science-imposed constraints were not violated. A review of existing Titan wind and atmosphere models and their physical background led to a subsequent parametric study of their impact on the supersonic entry phase, the parachute descent and finally the bodyfixed landing coordinates of the Probe. In addition to the deterministic (nominal) Probe trajectory, it is important to quantify the influence of various uncertainties that enter into the equations of motion on the results (e.g., state vectors, physical parameters of the environment and the Probe itself). This was done by propagating the system covariance matrix together with the nominal state vectors. A sophisticated Monte Carlo technique developed to save up computation time was then used to determine statistical percentiles of the key parameters. The Probe Orbiter link geometry was characterized by evaluating the link budget and received frequency at receiver level. In this calculation the spin of the Probe and the asymmetric gain pattern of the transmitting antennas was taken into account. The results were then used in a mathematical model that describes the tracking capability of the receiver symbol synchronizer. This allowed the loss of data during the mission to be quantified. A subsequent parametric study of different sets of mission parameters with the goal of minimizing the data losses and maximizing the overall mission robustness resulted in the recommendation to change the flyby altitude of the Orbiter from 65,000 km down to 60,000 km.

Mode control using two electrodes on HBT-EP

NASA Astrophysics Data System (ADS)

Stewart, I. G.; Brooks, J. W.; Levesque, J. P.; Mauel, M. E.; Navratil, G. A.

2017-10-01

Understanding the effects of plasma rotation on magnetohydrodynamic (MHD) modes and tokamak plasma stability is important for performance enhancement of current magnetic confinement experiments and to future fusion devices such as ITER. In order to control plasma rotation, two molybdenum electrodes have been installed on HBT-EP toroidally separated by 144 degrees. This allows independent biasing of the two probes both spatially and temporally. When the bias probes are inserted into the edge of the plasma and a voltage is applied, the probes drive radial currents and produce plasma flow from the torque induced by the currents. If the bias probe voltage is sufficiently positive, the MHD mode rotation transitions into a state with a rapid mode rotation frequency (in excess of 25 kHz) in the direction opposite to mode rotation without bias. The transition into this reversed rotation state occurs when the torque exceeds a threshold, which can depend upon the phase of an applied n = 1 error field. We present recent studies of the two-electrode system on mode rotation, mode stability, and the toroidal symmetry of the radial current through the scrape-off-layer (SOL) during MHD activity and applied magnetic perturbations. Supported by U.S. DOE Grant DE-FG02-86ER53222.

Probing the geometry of the Laughlin state

DOE PAGES

Johri, Sonika; Papic, Z.; Schmitteckert, P.; ...

2016-02-05

It has recently been pointed out that phases of matter with intrinsic topological order, like the fractional quantum Hall states, have an extra dynamical degree of freedom that corresponds to quantum geometry. Here we perform extensive numerical studies of the geometric degree of freedom for the simplest example of fractional quantumHall states—the filling v = 1/3 Laughlin state.We perturb the system by a smooth, spatially dependent metric deformation and measure the response of the Hall fluid, finding it to be proportional to the Gaussian curvature of the metric. Further, we generalize the concept of coherent states to formulate the bulkmore » off-diagonal long range order for the Laughlin state, and compute the deformations of the metric in the vicinity of the edge of the system. We introduce a ‘pair amplitude’ operator and show that it can be used to numerically determine the intrinsic metric of the Laughlin state. Furthermore, these various probes are applied to several experimentally relevant settings that can expose the quantum geometry of the Laughlin state, in particular to systems with mass anisotropy and in the presence of an electric field gradient.« less

Exploring hydrophobic subdomain IIA of the protein bovine serum albumin in the native, intermediate, unfolded, and refolded states by a small fluorescence molecular reporter.

PubMed

Paul, Bijan Kumar; Samanta, Anuva; Guchhait, Nikhil

2010-05-13

A simple intramolecular charge transfer (ICT) compound, 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid methyl ester (DPDAME), has been documented to be a potential molecular reporter for probing microheterogeneous environments of a model transport protein bovine serum albumin (BSA) using spectroscopic techniques. Meteoric modifications to the emission profile of DPDAME upon addition of BSA come out to be a result of its binding to hydrophobic subdomain IIA. The highly polarity-sensitive ICT emission of DPDAME is found to be a proficient extrinsic molecular reporter for efficient mapping of native, intermediate, unfolded, and refolded states of the protein. Experimental data coupled with a reinforcing support from theoretical simulation using CHARMM22 software confirm the binding site of the probe to be the subdomain IIA of BSA, while FRET study reveals a remarkably close approach of our extrinsic molecular reporter to Trp-212 (in domain IIA): the distance between DPDAME and Trp-212 is 1.437 nm. The caliber of DPDAME as an external fluorescence marker also extends to the depiction of protein-surfactant (BSA-SDS) interaction to commendable fruition. Additionally, the protective action of small amounts of SDS on urea-denatured protein is documented by polarity-sensitive ICT emission of the probe. The present study also reflects the enhancement of the stability of BSA with respect to chemically induced denaturation by urea as a result of binding to the probe DPDAME.

Water as probe molecule for midgap states in nanocrystalline strontium titanate by conventional and synchronous luminescence spectroscopy under ambient conditions

NASA Astrophysics Data System (ADS)

Taylor, Sean; Samokhvalov, Alexander

2017-03-01

Alkaline earth metal titanates are broad bandgap semiconductors with applications in electronic devices, as catalysts, photocatalysts, sorbents, and sensors. Strontium titanate SrTiO3 is of interest in electronic devices, sensors, in the photocatalytic hydrogen generation, as catalyst and sorbent. Both photocatalysis and operation of electronic devices rely upon the pathways of relaxation of excited charge in the semiconductor, including relaxation through the midgap states. We report characterization of nanocrystalline SrTiO3 at room temperature by "conventional" vs. synchronous luminescence spectroscopy and complementary methods. We determined energies of radiative transitions in the visible range through the two midgap states in the nanocrystalline SrTiO3. Further, adsorption and desorption of vapor of water as "probe molecule" for midgap states in the nanocrystalline SrTiO3 was studied, for the first time, by luminescence spectroscopy under ambient conditions. Emission of visible light from the nanocrystalline SrTiO3 is significantly increased upon desorption of water and decreased (quenched) upon adsorption of water vapor, due to interactions with the surface midgap states.

Synthesis and evaluation of new NIR-fluorescent probes for cathepsin B: ICT versus FRET as a turn-ON mode-of-action.

PubMed

Kisin-Finfer, Einat; Ferber, Shiran; Blau, Rachel; Satchi-Fainaro, Ronit; Shabat, Doron

2014-06-01

Recent years have seen tremendous progress in the design and study of molecular imaging geared towards biological and biomedical applications. The expression or activity of specific enzymes including proteases can be monitored by cutting edge molecular imaging techniques. Cathepsin B plays key roles in tumor progression via controlled degradation of extracellular matrix. Consequently, this protease has been attracting significant attention in cancer research, and many imaging probes targeting its activity have been developed. Here, we describe the design, synthesis and evaluation of two novel near infrared (NIR) fluorescent probes for detection of cathepsin B activity with different turn-ON mechanisms. One probe is based on an ICT activation mechanism of a donor-two-acceptor π-electron dye system, while the other is based on the FRET mechanism obtained by a fluorescent dye and a quencher. The two probes exhibit significant fluorescent turn-ON response upon cleavage by cathepsin B. The NIR fluorescence of the ICT probe in its OFF state was significantly lower than that of the FRET-based probe. This effect results in a higher signal-to-noise ratio and consequently increased sensitivity and better image contrast. Copyright © 2014 Elsevier Ltd. All rights reserved.

Ultrafast electron-optical phonon scattering and quasiparticle lifetime in CVD-grown graphene.

PubMed

Shang, Jingzhi; Yu, Ting; Lin, Jianyi; Gurzadyan, Gagik G

2011-04-26

Ultrafast quasiparticle dynamics in graphene grown by chemical vapor deposition (CVD) has been studied by UV pump/white-light probe spectroscopy. Transient differential transmission spectra of monolayer graphene are observed in the visible probe range (400-650 nm). Kinetics of the quasiparticle (i.e., low-energy single-particle excitation with renormalized energy due to electron-electron Coulomb, electron-optical phonon (e-op), and optical phonon-acoustic phonon (op-ap) interactions) was monitored with 50 fs resolution. Extending the probe range to near-infrared, we find the evolution of quasiparticle relaxation channels from monoexponential e-op scattering to double exponential decay due to e-op and op-ap scattering. Moreover, quasiparticle lifetimes of mono- and randomly stacked graphene films are obtained for the probe photon energies continuously from 1.9 to 2.3 eV. Dependence of quasiparticle decay rate on the probe energy is linear for 10-layer stacked graphene films. This is due to the dominant e-op intervalley scattering and the linear density of states in the probed electronic band. A dimensionless coupling constant W is derived, which characterizes the scattering strength of quasiparticles by lattice points in graphene.

Excited state absorption spectra of dissolved and aggregated distyrylbenzene: A TD-DFT state and vibronic analysis

NASA Astrophysics Data System (ADS)

Oliveira, Eliezer Fernando; Shi, Junqing; Lavarda, Francisco Carlos; Lüer, Larry; Milián-Medina, Begoña; Gierschner, Johannes

2017-07-01

A time-dependent density functional theory study is performed to reveal the excited state absorption (ESA) features of distyrylbenzene (DSB), a prototype π-conjugated organic oligomer. Starting with a didactic insight to ESA based on simple molecular orbital and configuration considerations, the performance of various density functional theory functionals is tested to reveal the full vibronic ESA features of DSB at short and long probe delay times.

Measurement Of Molecular Mobilities Of Polymers

NASA Technical Reports Server (NTRS)

Kim, Soon Sam; Tsay, Fun-Dow

1989-01-01

New molecular-probe technique used to measure molecular mobility of polymer. Method based on use of time-resolved electron-spin resonance (ESR) spectroscopy to monitor decay of transient nutation amplitudes from photoexcited triplet states of probe molecules with which polymer is doped. The higher molecular mobility of polymer matrix, the faster nutation amplitudes of the probe molecules decay.

EXAFS: New tool for study of battery and fuel cell materials

NASA Technical Reports Server (NTRS)

Mcbreen, James; Ogrady, William E.; Pandya, Kaumudi I.

1987-01-01

Extended X ray absorption fine structure (EXAFS) is a powerful technique for probing the local atomic structure of battery and fuel cell materials. The major advantages of EXAFS are that both the probe and the signal are X rays and the technique is element selective and applicable to all states of matter. This permits in situ studies of electrodes and determination of the structure of single components in composite electrodes, or even complete cells. EXAFS specifically probes short range order and yields coordination numbers, bond distances, and chemical identity of nearest neighbors. Thus, it is ideal for structural studies of ions in solution and the poorly crystallized materials that are often the active materials or catalysts in batteries and fuel cells. Studies on typical battery and fuel cell components are used to describe the technique and the capability of EXAFS as a structural tool in these applications. Typical experimental and data analysis procedures are outlined. The advantages and limitations of the technique are also briefly discussed.

Dynamics of one-state downhill protein folding.

PubMed

Li, Peng; Oliva, Fabiana Y; Naganathan, Athi N; Muñoz, Victor

2009-01-06

The small helical protein BBL has been shown to fold and unfold in the absence of a free energy barrier according to a battery of quantitative criteria in equilibrium experiments, including probe-dependent equilibrium unfolding, complex coupling between denaturing agents, characteristic DSC thermogram, gradual melting of secondary structure, and heterogeneous atom-by-atom unfolding behaviors spanning the entire unfolding process. Here, we present the results of nanosecond T-jump experiments probing backbone structure by IR and end-to-end distance by FRET. The folding dynamics observed with these two probes are both exponential with common relaxation times but have large differences in amplitude following their probe-dependent equilibrium unfolding. The quantitative analysis of amplitude and relaxation time data for both probes shows that BBL folding dynamics are fully consistent with the one-state folding scenario and incompatible with alternative models involving one or several barrier crossing events. At 333 K, the relaxation time for BBL is 1.3 micros, in agreement with previous folding speed limit estimates. However, late folding events at room temperature are an order of magnitude slower (20 micros), indicating a relatively rough underlying energy landscape. Our results in BBL expose the dynamic features of one-state folding and chart the intrinsic time-scales for conformational motions along the folding process. Interestingly, the simple self-averaging folding dynamics of BBL are the exact dynamic properties required in molecular rheostats, thus supporting a biological role for one-state folding.

Dynamics of harpooning studied by transition state spectroscopy. II. LiṡṡFH

NASA Astrophysics Data System (ADS)

Hudson, A. J.; Oh, H. B.; Polanyi, J. C.; Piecuch, P.

2000-12-01

The van der Waals complex LiṡṡFH was formed in crossed beams and the transition state of the excited-state reaction, Li*(2p 2P)+HF→LiF+H, was accessed by photoexcitation of this complex. The dynamics of the excited-state reaction were probed by varying the excitation wavelength over the range 570-970 nm while recording the photodepletion of the complex. The findings were interpreted using high-level ab initio calculations of the ground and lowest excited-state potential-energy surfaces.

An excited-state intramolecular photon transfer fluorescence probe for localizable live cell imaging of cysteine

NASA Astrophysics Data System (ADS)

Liu, Wei; Chen, Wen; Liu, Si-Jia; Jiang, Jian-Hui

2017-03-01

Small molecule probes suitable for selective and specific fluorescence imaging of some important but low-concentration intracellular reactive sulfur species such as cysteine (Cys) pose a challenge in chemical biology. We present a readily available, fast-response fluorescence probe CHCQ-Ac, with 2-(5‧-chloro-2-hydroxyl-phenyl)-6-chloro-4(3 H)-quinazolinone (CHCQ) as the fluorophore and acrylate group as the functional moiety, that enables high-selectivity and high-sensitivity for detecting Cys in both solution and biological system. After specifically reacted with Cys, the probe undergoes a seven-membered intramolecular cyclization and released the fluorophore CHCQ with excited-state intramolecular photon transfer effect. A highly fluorescent, insoluble aggregate was then formed to facilitate high-sensitivity and high-resolution imaging. The results showed that probe CHCQ-Ac affords a remarkably large Stokes shift and can detect Cys under physiological pH condition with no interference from other analytes. Moreover, this probe was proved to have excellent chemical stability, low cytotoxicity and good cell permeability. Our design of this probe provides a novel potential tool to visualize and localize cysteine in bioimaging of live cells that would greatly help to explore various Cys-related physiological and pathological cellular processes in cell biology and diagnostics.

Fluorinated Paramagnetic Complexes: Sensitive and Responsive Probes for Magnetic Resonance Spectroscopy and Imaging

NASA Astrophysics Data System (ADS)

Peterson, Katie L.; Srivastava, Kriti; Pierre, Valérie C.

2018-05-01

Fluorine magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI) of chemical and physiological processes is becoming more widespread. The strength of this technique comes from the negligible background signal in in vivo 19F MRI and the large chemical shift window of 19F that enables it to image concomitantly more than one marker. These same advantages have also been successfully exploited in the design of responsive 19F probes. Part of the recent growth of this technique can be attributed to novel designs of 19F probes with improved imaging parameters due to the incorporation of paramagnetic metal ions. In this review, we provide a description of the theories and strategies that have been employed successfully to improve the sensitivity of 19F probes with paramagnetic metal ions. The Bloch-Wangsness-Redfield theory accurately predicts how molecular parameters such as distance, geometry, rotational correlation times, as well as the nature, oxidation state, and spin state of the metal ion affect the sensitivity of the fluorine-based probes. The principles governing the design of responsive 19F probes are subsequently described in a “how to” guide format. Examples of such probes and their advantages and disadvantages are highlighted through a synopsis of the literature.

Generalized Hofmann quantum process fidelity bounds for quantum filters

NASA Astrophysics Data System (ADS)

Sedlák, Michal; Fiurášek, Jaromír

2016-04-01

We propose and investigate bounds on the quantum process fidelity of quantum filters, i.e., probabilistic quantum operations represented by a single Kraus operator K . These bounds generalize the Hofmann bounds on the quantum process fidelity of unitary operations [H. F. Hofmann, Phys. Rev. Lett. 94, 160504 (2005), 10.1103/PhysRevLett.94.160504] and are based on probing the quantum filter with pure states forming two mutually unbiased bases. Determination of these bounds therefore requires far fewer measurements than full quantum process tomography. We find that it is particularly suitable to construct one of the probe bases from the right eigenstates of K , because in this case the bounds are tight in the sense that if the actual filter coincides with the ideal one, then both the lower and the upper bounds are equal to 1. We theoretically investigate the application of these bounds to a two-qubit optical quantum filter formed by the interference of two photons on a partially polarizing beam splitter. For an experimentally convenient choice of factorized input states and measurements we study the tightness of the bounds. We show that more stringent bounds can be obtained by more sophisticated processing of the data using convex optimization and we compare our methods for different choices of the input probe states.

Near-Infrared Excited State Dynamics of Melanins: The Effects of Iron Content, Photo-Damage, Chemical Oxidation, and Aggregate Size

PubMed Central

2015-01-01

Ultrafast pump–probe measurements can discriminate the two forms of melanin found in biological tissue (eumelanin and pheomelanin), which may be useful for diagnosing and grading melanoma. However, recent work has shown that bound iron content changes eumelanin’s pump–probe response, making it more similar to that of pheomelanin. Here we record the pump–probe response of these melanins at a wider range of wavelengths than previous work and show that with shorter pump wavelengths the response crosses over from being dominated by ground-state bleaching to being dominated by excited-state absorption. The crossover wavelength is different for each type of melanin. In our analysis, we found that the mechanism by which iron modifies eumelanin’s pump–probe response cannot be attributed to Raman resonances or differences in melanin aggregation and is more likely caused by iron acting to broaden the unit spectra of individual chromophores in the heterogeneous melanin aggregate. We analyze the dependence on optical intensity, finding that iron-loaded eumelanin undergoes irreversible changes to the pump–probe response after intense laser exposure. Simultaneously acquired fluorescence data suggest that the previously reported “activation” of eumelanin fluorescence may be caused in part by the dissociation of metal ions or the selective degradation of iron-containing melanin. PMID:24446774

Bias stress in PDI-CN2 and P3HT studied with Kelvin Probe Force Microscopy

NASA Astrophysics Data System (ADS)

Cao, Minxuan; Moscatello, Jason; Castaneda, Chloe; Xue, Binglan; Usluer, Ozlem; Briseno, Alejandro; Aidala, Katherine

We have developed a technique that uses scanning probe microscopy (SPM) to study the real-time injection and extraction of charge carriers in organic semiconductor devices. We investigate PDI-CN2 and P3HT in a back gate field effect transistor geometry with gold electrodes. By positioning the SPM tip at an individual location and using Kelvin probe microscopy to record the potential over time, we can record how the charge carriers respond to changing the gate voltage while the source and drain electrodes are grounded. We see relatively fast screening when carriers are injected into the film. The screening is slower when carriers must escape from traps to exit the film. By incrementally stepping the gate voltage, we can probe different trap depths. By repeating the measurement, we observe the development of longer lived trap states, shown by the longer time recorded to fully screen the gate voltage. This work is supported by NSF Grant DMR-0955348, and the Center for Heirarchical Manufacturing at the University of Massachusetts, Amherst (NSF CMMI-1025020).

Mid-infrared picosecond pump-dump-probe and pump-repump-probe experiments to resolve a ground-state intermediate in cyanobacterial phytochrome Cph1.

PubMed

van Wilderen, Luuk J G W; Clark, Ian P; Towrie, Michael; van Thor, Jasper J

2009-12-24

Multipulse picosecond mid-infrared spectroscopy has been used to study photochemical reactions of the cyanobacterial phytochrome photoreceptor Cph1. Different photophysical schemes have been discussed in the literature to describe the pathways after photoexcitation, particularly, to identify reaction phases that are linked to photoisomerisation and electronic decay in the 1566-1772 cm(-1) region that probes C=C and C=O stretching modes of the tetrapyrrole chromophore. Here, multipulse spectroscopy is employed, where, compared to conventional visible pump-mid-infrared probe spectroscopy, an additional visible pulse is incorporated that interacts with populations that are evolving on the excited- and ground-state potential energy surfaces. The time delays between the pump and the dump pulse are chosen such that the dump pulse interacts with different phases in the reaction process. The pump and dump pulses are at the same wavelength, 640 nm, and are resonant with the Pr ground state as well as with the excited state and intermediates. Because the dump pulse additionally pumps the remaining, partially recovered, and partially oriented ground-state population, theory is developed for estimating the fraction of excited-state molecules. The calculations take into account the model-dependent ground-state recovery fraction, the angular dependence of the population transfer resulting from the finite bleach that occurs with linearly polarized intense femtosecond optical excitation, and the partially oriented population for the dump field. Distinct differences between the results from the experiments that use a 1 or a 14 ps dump time favor a branching evolution from S1 to an excited state or reconfigured chromophore and to a newly identified ground-state intermediate (GSI). Optical dumping at 1 ps shows the instantaneous induced absorption of a delocalized C=C stretching mode at 1608 cm(-1), where the increased cross section is associated with the electronic ground-state structure of the ZZZ configuration of the linear tetrapyrrole chromophore. The dump-induced absorption decays with time constants of 5 and 19 ps to the Pr ground state. Employing a dump pulse at 14 ps results in an instantaneous decrease of the absorption of the 1608 cm(-1) band, indicating repumping of the GSI. The dump-induced absorption recovers back to the GSI with a 6 ps lifetime. A spectral similarity is observed between the 6 ps phase in the dump experiment and the 3 ps component found in the two-pulse pump-probe measurement. Combined with the dominance of ground-state absorption bands in the dump-induced spectrum, this indicates the presence of a GSI, which is additionally characterized by previously unidentified induced absorption at 1710 and 1570-80 cm(-1). The metastable photoproduct Lumi-R, which is in the electronic ground state and populated at 500 ps after excitation of Pr, is highly efficiently repumped into the Pr ground state with the power density used. After repumping, Lumi-R is not recovered on the 500 ps time scale of the experiment and is distinct from the GSI of Pr since it is not associated with its characteristic induced absorption at 1710 and 1570-80 cm(-1).

High Aspect-Ratio Neural Probes using Conventional Blade Dicing

NASA Astrophysics Data System (ADS)

Goncalves, S. B.; Ribeiro, J. F.; Silva, A. F.; Correia, J. H.

2016-10-01

Exploring deep neural circuits has triggered the development of long penetrating neural probes. Moreover, driven by brain displacement, the long neural probes require also a high aspect-ratio shafts design. In this paper, a simple and reproducible method of manufacturing long-shafts neural probes using blade dicing technology is presented. Results shows shafts up to 8 mm long and 200 µm wide, features competitive to the current state-of-art, being its outline simply accomplished by a single blade dicing program. Therefore, conventional blade dicing presents itself as a viable option to manufacture long neural probes.

Low energy positrons as probes of reconstructed semiconductor surfaces.

NASA Astrophysics Data System (ADS)

Fazleev, Nail G.; Weiss, Alex H.

2007-03-01

Positron probes of semiconductor surfaces that play a fundamental role in modern science and technology are capable to non-destructively provide information that is both unique to the probe and complimentary to that extracted using other more standard techniques. We discuss recent progress in studies of the reconstructed Si(100), Si(111), Ge(100), and Ge(111) surfaces, clean and exposed to hydrogen and oxygen, using a surface characterization technique, Positron-Annihilation-Induced Auger-Electron Spectroscopy (PAES). Experimental PAES results are analyzed by performing first-principles calculations of positron surface states and annihilation probabilities of surface-trapped positrons with relevant core electrons for the reconstructed surfaces, taking into account discrete lattice effects, the electronic reorganization due to bonding, and charge redistribution effects at the surface. Effects of the hydrogen and oxygen adsorption on semiconductor surfaces on localization of positron surface state wave functions and annihilation characteristics are also analyzed. Theoretical calculations confirm that PAES intensities, which are proportional to annihilation probabilities of the surface trapped positrons that results in a core hole, are sensitive to the crystal face, surface structure and elemental content of the semiconductors.

Live-Cell Imaging of DNA Methylation Based on Synthetic-Molecule/Protein Hybrid Probe.

PubMed

Kumar, Naresh; Hori, Yuichiro; Kikuchi, Kazuya

2018-06-04

The epigenetic modification of DNA involves the conversion of cytosine to 5-methylcytosine, also known as DNA methylation. DNA methylation is important in modulating gene expression and thus, regulating genome and cellular functions. Recent studies have shown that aberrations in DNA methylation are associated with various epigenetic disorders or diseases including cancer. This stimulates great interest in the development of methods that can detect and visualize DNA methylation. For instance, fluorescent proteins (FPs) in conjugation with methyl-CpG-binding domain (MBD) have been employed for live-cell imaging of DNA methylation. However, the FP-based approach showed fluorescence signals for both the DNA-bound and -unbound states and thus differentiation between these states is difficult. Synthetic-molecule/protein hybrid probes can provide an alternative to overcome this restriction. In this article, we discuss the synthetic-molecule/protein hybrid probe that we developed recently for live-cell imaging of DNA methylation, which exhibited fluorescence enhancement only after binding to methylated DNA. © 2018 The Chemical Society of Japan & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Location of fluorescent probes (2'-hydroxy derivatives of 2,5-diaryl-1,3-oxazole) in lipid membrane studied by fluorescence spectroscopy and molecular dynamics simulation.

PubMed

Posokhov, Yevgen; Kyrychenko, Alexander

2018-04-01

2'-Hydroxy derivatives of 2,5-diaryl-1,3-oxazole are known as environment-sensitive ratiometric excited-state intramolecular proton transfer (ESIPT) fluorescent probes, which are used to monitor physicochemical properties of lipid membranes. However, because of their heterogeneous membrane distribution, accurate experimental determination of the probe position is difficult. To estimate the location of the ESIPT probes in lipid membranes we have performed fluorescence measurements and molecular dynamics (MD) simulations. In the series composed of 2-(2'-hydroxy-phenyl)-5-phenyl-1,3-oxazole (1), 2-(2'-hydroxy-phenyl)-5-(4'-biphenyl)-1,3-oxazole (2), and 2-(2'-hydroxy-phenyl)-phenanthro[9,10-d]-1,3-oxazole (3), the structure of the ESIPT-moiety of 2-(2'-hydroxy-phenyl)-oxazole was varied by either aromatic ring substitution or annealing, leading to the systematical increase in the hydrophobic character of the probes. The comparison of the fluorescence behavior of probes 1-3 in a wide variety of solvents with those in phospholipid vesicles revealed that all three probes prefer to reside inside a membrane. Our MD results demonstrate that the probes locate from the glycerol residues and the polar carbonyl groups of phospholipids up to hydrophobic acyl chain units. It has been found that the probe location correlates well with the size of the aromatic moiety, being gradually shifted from 11.1 Å to 7.6 Å from the bilayer center for probes 1 to 3, respectively. Our results may be useful for the design of novel fluorescent probes for fluorescence sensing of specific regions within a lipid membrane. Copyright © 2018 Elsevier B.V. All rights reserved.

Determination of cell metabolite VEGF₁₆₅ and dynamic analysis of protein-DNA interactions by combination of microfluidic technique and luminescent switch-on probe.

PubMed

Lin, Xuexia; Leung, Ka-Ho; Lin, Ling; Lin, Luyao; Lin, Sheng; Leung, Chung-Hang; Ma, Dik-Lung; Lin, Jin-Ming

2016-05-15

In this paper, we rationally design a novel G-quadruplex-selective luminescent iridium (III) complex for rapid detection of oligonucleotide and VEGF165 in microfluidics. This new probe is applied as a convenient biosensor for label-free quantitative analysis of VEGF165 protein from cell metabolism, as well as for studying the kinetics of the aptamer-protein interaction combination with a microfluidic platform. As a result, we have successfully established a quantitative analysis of VEGF165 from cell metabolism. Furthermore, based on the principles of hydrodynamic focusing and diffusive mixing, different transient states during kinetics process were monitored and recorded. Thus, the combination of microfluidic technique and G-quadruplex luminescent probe will be potentially applied in the studies of intramolecular interactions and molecule recognition in the future. Copyright © 2015 Elsevier B.V. All rights reserved.

Application of activity-based protein profiling to study enzyme function in adipocytes.

PubMed

Galmozzi, Andrea; Dominguez, Eduardo; Cravatt, Benjamin F; Saez, Enrique

2014-01-01

Activity-based protein profiling (ABPP) is a chemical proteomics approach that utilizes small-molecule probes to determine the functional state of enzymes directly in native systems. ABPP probes selectively label active enzymes, but not their inactive forms, facilitating the characterization of changes in enzyme activity that occur without alterations in protein levels. ABPP can be a tool superior to conventional gene expression and proteomic profiling methods to discover new enzymes active in adipocytes and to detect differences in the activity of characterized enzymes that may be associated with disorders of adipose tissue function. ABPP probes have been developed that react selectively with most members of specific enzyme classes. Here, using as an example the serine hydrolase family that includes many enzymes with critical roles in adipocyte physiology, we describe methods to apply ABPP analysis to the study of adipocyte enzymatic pathways. © 2014 Elsevier Inc. All rights reserved.

Probe activities. Annual report, July 1, 1975--June 30, 1976. [Veterinary medicine

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sanders, W.M.; Saunders, G.C.; Bartlett, M.L.

1976-12-01

Small-scale experiments and feasibility studies were performed for the Animal and Plant Health Inspection Service (APHIS) of the United States Department of Agriculture (USDA). Included were computer support for the payment of indemnity for brucellosis in Texas; the measurement of cattle ear canal temperatures and its automation was continued at the Veterinary Services Laboratory (VSL), Ames, IA; and two short serological probes experiments were supported. Also funds were transferred to support the Electronic Identification Project to enable this work to continue without interruption.

The First Interlaced Continuum Robot, Devised to Intrinsically Follow the Leader

PubMed Central

Kang, Byungjeon; Kojcev, Risto; Sinibaldi, Edoardo

2016-01-01

Flexible probes that are safely deployed to hard-to-reach targets while avoiding critical structures are strategic in several high-impact application fields, including the biomedical sector and the sector of inspections at large. A critical problem for these tools is the best approach for deploying an entire tool body, not only its tip, on a sought trajectory. A probe that achieves this deployment is considered to follow the leader (or to achieve follow-the-leader deployment) because its body sections follow the track traced by its tip. Follow-the-leader deployment through cavities is complicated due to a lack of external supports. Currently, no definitive implementation for a probe that is intrinsically able to follow the leader, i.e., without relying on external supports, has been achieved. In this paper, we present a completely new device, namely the first interlaced continuum robot, devised to intrinsically follow the leader. We developed the interlaced configuration by pursuing a conceptual approach irrespective of application-specific constraints and assuming two flexible tools with controllable stiffness. We questioned the possibility of solving the previously mentioned deployment problem by harnessing probe symmetry during the design process. This study examines the entire development of the novel interlaced probe: model-based conceptual design, detailed design and prototyping, and preliminary experimental assessment. Our probe can build a track with a radius of curvature that is as small as twice the probe diameter, which enables it to outperform state-of-the-art tools that are aimed at follow-the-leader deployment. Despite the limitations that are inherently associated with its original character, this study provides a prototypical approach to the design of interlaced continuum systems and demonstrates the first interlaced continuum probe, which is intrinsically able to follow the leader. PMID:26914328

The First Interlaced Continuum Robot, Devised to Intrinsically Follow the Leader.

PubMed

Kang, Byungjeon; Kojcev, Risto; Sinibaldi, Edoardo

2016-01-01

Flexible probes that are safely deployed to hard-to-reach targets while avoiding critical structures are strategic in several high-impact application fields, including the biomedical sector and the sector of inspections at large. A critical problem for these tools is the best approach for deploying an entire tool body, not only its tip, on a sought trajectory. A probe that achieves this deployment is considered to follow the leader (or to achieve follow-the-leader deployment) because its body sections follow the track traced by its tip. Follow-the-leader deployment through cavities is complicated due to a lack of external supports. Currently, no definitive implementation for a probe that is intrinsically able to follow the leader, i.e., without relying on external supports, has been achieved. In this paper, we present a completely new device, namely the first interlaced continuum robot, devised to intrinsically follow the leader. We developed the interlaced configuration by pursuing a conceptual approach irrespective of application-specific constraints and assuming two flexible tools with controllable stiffness. We questioned the possibility of solving the previously mentioned deployment problem by harnessing probe symmetry during the design process. This study examines the entire development of the novel interlaced probe: model-based conceptual design, detailed design and prototyping, and preliminary experimental assessment. Our probe can build a track with a radius of curvature that is as small as twice the probe diameter, which enables it to outperform state-of-the-art tools that are aimed at follow-the-leader deployment. Despite the limitations that are inherently associated with its original character, this study provides a prototypical approach to the design of interlaced continuum systems and demonstrates the first interlaced continuum probe, which is intrinsically able to follow the leader.

Near Infrared Emission of Highly Electronically Excited CO: A Sensitive Probe to Study the Interstellar Medium??

NASA Technical Reports Server (NTRS)

Gudipati, Murthy S.

2002-01-01

Among the various spectroscopic features of the second most abundant molecule in the space, CO, "the triplet - triplet transitions involving the lowest triplet state a(sup 3)II and the higher-lying a(sup 1)3 SIGMA (sup +), d(sup 3) (DELTA), e (sup 3) SIGMA (sup -) states spanning near-UV to mid-IR spectral range" have so far not been explored in astrophysical observations. The energies of these transitions are highly sensitive to the surroundings in which CO exists, i.e. gas-phase, polar or non-polar condensed phase. It is proposed here that these triplet-triplet emission/absorption bands can be used as a sensitive probe to investigate the local environments of CO, whether in the planetary atmosphere, stellar atmosphere or interstellar medium.

Kinetics of exchange between zero-, one-, and two-hydrogen-bonded states of methyl and ethyl acetate in methanol.

PubMed

Chuntonov, Lev; Pazos, Ileana M; Ma, Jianqiang; Gai, Feng

2015-03-26

It has recently been shown that the ester carbonyl stretching vibration can be used as a sensitive probe of local electrostatic field in molecular systems. To further characterize this vibrational probe and extend its potential applications, we studied the kinetics of chemical exchange between differently hydrogen-bonded (H-bonded) ester carbonyl groups of methyl acetate (MA) and ethyl acetate (EA) in methanol. We found that, while both MA and EA can form zero, one, or two H-bonds with the solvent, the population of the 2hb state in MA is significantly smaller than that in EA. Using a combination of linear and nonlinear infrared measurements and numerical simulations, we further determined the rate constants for the exchange between these differently H-bonded states. We found that for MA the chemical exchange reaction between the two dominant states (i.e., 0hb and 1hb states) has a relaxation rate constant of 0.14 ps(-1), whereas for EA the three-state chemical exchange reaction occurs in a predominantly sequential manner with the following relaxation rate constants: 0.11 ps(-1) for exchange between 0hb and 1hb states and 0.12 ps(-1) for exchange between 1hb and 2hb states.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Holdaway, David I. H., E-mail: d.holdaway@ucl.ac.uk; Olaya-Castro, Alexandra, E-mail: a.olaya@ucl.ac.uk; Collini, Elisabetta, E-mail: elisabetta.collini@unipd.it

We examine transient circular dichroism (TRCD) spectroscopy as a technique to investigate signatures of exciton coherence dynamics under the influence of structured vibrational environments. We consider a pump-probe configuration with a linearly polarized pump and a circularly polarized probe, with a variable angle θ between the two directions of propagation. In our theoretical formalism the signal is decomposed in chiral and achiral doorway and window functions. Using this formalism, we show that the chiral doorway component, which beats during the population time, can be isolated by comparing signals with different values of θ. As in the majority of time-resolved pump-probemore » spectroscopy, the overall TRCD response shows signatures of both excited and ground state dynamics. However, we demonstrate that the chiral doorway function has only a weak ground state contribution, which can generally be neglected if an impulsive pump pulse is used. These findings suggest that the pump-probe configuration of optical TRCD in the impulsive limit has the potential to unambiguously probe quantum coherence beating in the excited state. We present numerical results for theoretical signals in an example dimer system.« less

Using a biased qubit to probe complex systems

NASA Astrophysics Data System (ADS)

Pollock, Felix A.; Checińska, Agata; Pascazio, Saverio; Modi, Kavan

2016-09-01

Complex mesoscopic systems play increasingly important roles in modern science, from understanding biological functions at the molecular level to designing solid-state information processing devices. The operation of these systems typically depends on their energetic structure, yet probing their energy landscape can be extremely challenging; they have many degrees of freedom, which may be hard to isolate and measure independently. Here, we show that a qubit (a two-level quantum system) with a biased energy splitting can directly probe the spectral properties of a complex system, without knowledge of how they couple. Our work is based on the completely positive and trace-preserving map formalism, which treats any unknown dynamics as a "black-box" process. This black box contains information about the system with which the probe interacts, which we access by measuring the survival probability of the initial state of the probe as function of the energy splitting and the process time. Fourier transforming the results yields the energy spectrum of the complex system. Without making assumptions about the strength or form of its coupling, our probe could determine aspects of a complex molecule's energy landscape as well as, in many cases, test for coherent superposition of its energy eigenstates.

The von Neumann model of measurement in quantum mechanics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mello, Pier A.

2014-01-08

We describe how to obtain information on a quantum-mechanical system by coupling it to a probe and detecting some property of the latter, using a model introduced by von Neumann, which describes the interaction of the system proper with the probe in a dynamical way. We first discuss single measurements, where the system proper is coupled to one probe with arbitrary coupling strength. The goal is to obtain information on the system detecting the probe position. We find the reduced density operator of the system, and show how Lüders rule emerges as the limiting case of strong coupling. The vonmore » Neumann model is then generalized to two probes that interact successively with the system proper. Now we find information on the system by detecting the position-position and momentum-position correlations of the two probes. The so-called 'Wigner's formula' emerges in the strong-coupling limit, while 'Kirkwood's quasi-probability distribution' is found as the weak-coupling limit of the above formalism. We show that successive measurements can be used to develop a state-reconstruction scheme. Finally, we find a generalized transform of the state and the observables based on the notion of successive measurements.« less

Designing Flavoprotein-GFP Fusion Probes for Analyte-Specific Ratiometric Fluorescence Imaging.

PubMed

Hudson, Devin A; Caplan, Jeffrey L; Thorpe, Colin

2018-02-20

The development of genetically encoded fluorescent probes for analyte-specific imaging has revolutionized our understanding of intracellular processes. Current classes of intracellular probes depend on the selection of binding domains that either undergo conformational changes on analyte binding or can be linked to thiol redox chemistry. Here we have designed novel probes by fusing a flavoenzyme, whose fluorescence is quenched on reduction by the analyte of interest, with a GFP domain to allow for rapid and specific ratiometric sensing. Two flavoproteins, Escherichia coli thioredoxin reductase and Saccharomyces cerevisiae lipoamide dehydrogenase, were successfully developed into thioredoxin and NAD + /NADH specific probes, respectively, and their performance was evaluated in vitro and in vivo. A flow cell format, which allowed dynamic measurements, was utilized in both bacterial and mammalian systems. In E. coli the first reported intracellular steady-state of the cytoplasmic thioredoxin pool was measured. In HEK293T mammalian cells, the steady-state cytosolic ratio of NAD + /NADH induced by glucose was determined. These genetically encoded fluorescent constructs represent a modular approach to intracellular probe design that should extend the range of metabolites that can be quantitated in live cells.

Experimental aspect of solid-state nuclear magnetic resonance studies of biomaterials such as bones.

PubMed

Singh, Chandan; Rai, Ratan Kumar; Sinha, Neeraj

2013-01-01

Solid-state nuclear magnetic resonance (SSNMR) spectroscopy is increasingly becoming a popular technique to probe micro-structural details of biomaterial such as bone with pico-meter resolution. Due to high-resolution structural details probed by SSNMR methods, handling of bone samples and experimental protocol are very crucial aspects of study. We present here first report of the effect of various experimental protocols and handling methods of bone samples on measured SSNMR parameters. Various popular SSNMR experiments were performed on intact cortical bone sample collected from fresh animal, immediately after removal from animal systems, and results were compared with bone samples preserved in different conditions. We find that the best experimental conditions for SSNMR parameters of bones correspond to preservation at -20 °C and in 70% ethanol solution. Various other SSNMR parameters were compared corresponding to different experimental conditions. Our study has helped in finding best experimental protocol for SSNMR studies of bone. This study will be of further help in the application of SSNMR studies on large bone disease related animal model systems for statistically significant results. © 2013 Elsevier Inc. All rights reserved.

Comprehensive multiphase NMR spectroscopy: Basic experimental approaches to differentiate phases in heterogeneous samples

NASA Astrophysics Data System (ADS)

Courtier-Murias, Denis; Farooq, Hashim; Masoom, Hussain; Botana, Adolfo; Soong, Ronald; Longstaffe, James G.; Simpson, Myrna J.; Maas, Werner E.; Fey, Michael; Andrew, Brian; Struppe, Jochem; Hutchins, Howard; Krishnamurthy, Sridevi; Kumar, Rajeev; Monette, Martine; Stronks, Henry J.; Hume, Alan; Simpson, André J.

2012-04-01

Heterogeneous samples, such as soils, sediments, plants, tissues, foods and organisms, often contain liquid-, gel- and solid-like phases and it is the synergism between these phases that determine their environmental and biological properties. Studying each phase separately can perturb the sample, removing important structural information such as chemical interactions at the gel-solid interface, kinetics across boundaries and conformation in the natural state. In order to overcome these limitations a Comprehensive Multiphase-Nuclear Magnetic Resonance (CMP-NMR) probe has been developed, and is introduced here, that permits all bonds in all phases to be studied and differentiated in whole unaltered natural samples. The CMP-NMR probe is built with high power circuitry, Magic Angle Spinning (MAS), is fitted with a lock channel, pulse field gradients, and is fully susceptibility matched. Consequently, this novel NMR probe has to cover all HR-MAS aspects without compromising power handling to permit the full range of solution-, gel- and solid-state experiments available today. Using this technology, both structures and interactions can be studied independently in each phase as well as transfer/interactions between phases within a heterogeneous sample. This paper outlines some basic experimental approaches using a model heterogeneous multiphase sample containing liquid-, gel- and solid-like components in water, yielding separate 1H and 13C spectra for the different phases. In addition, 19F performance is also addressed. To illustrate the capability of 19F NMR soil samples, containing two different contaminants, are used, demonstrating a preliminary, but real-world application of this technology. This novel NMR approach possesses a great potential for the in situ study of natural samples in their native state.

Comprehensive multiphase NMR spectroscopy: basic experimental approaches to differentiate phases in heterogeneous samples.

PubMed

Courtier-Murias, Denis; Farooq, Hashim; Masoom, Hussain; Botana, Adolfo; Soong, Ronald; Longstaffe, James G; Simpson, Myrna J; Maas, Werner E; Fey, Michael; Andrew, Brian; Struppe, Jochem; Hutchins, Howard; Krishnamurthy, Sridevi; Kumar, Rajeev; Monette, Martine; Stronks, Henry J; Hume, Alan; Simpson, André J

2012-04-01

Heterogeneous samples, such as soils, sediments, plants, tissues, foods and organisms, often contain liquid-, gel- and solid-like phases and it is the synergism between these phases that determine their environmental and biological properties. Studying each phase separately can perturb the sample, removing important structural information such as chemical interactions at the gel-solid interface, kinetics across boundaries and conformation in the natural state. In order to overcome these limitations a Comprehensive Multiphase-Nuclear Magnetic Resonance (CMP-NMR) probe has been developed, and is introduced here, that permits all bonds in all phases to be studied and differentiated in whole unaltered natural samples. The CMP-NMR probe is built with high power circuitry, Magic Angle Spinning (MAS), is fitted with a lock channel, pulse field gradients, and is fully susceptibility matched. Consequently, this novel NMR probe has to cover all HR-MAS aspects without compromising power handling to permit the full range of solution-, gel- and solid-state experiments available today. Using this technology, both structures and interactions can be studied independently in each phase as well as transfer/interactions between phases within a heterogeneous sample. This paper outlines some basic experimental approaches using a model heterogeneous multiphase sample containing liquid-, gel- and solid-like components in water, yielding separate (1)H and (13)C spectra for the different phases. In addition, (19)F performance is also addressed. To illustrate the capability of (19)F NMR soil samples, containing two different contaminants, are used, demonstrating a preliminary, but real-world application of this technology. This novel NMR approach possesses a great potential for the in situ study of natural samples in their native state. Copyright © 2012 Elsevier Inc. All rights reserved.

Vibrational wave packets in the B 1Πu and D 1Σu+ states of Cs2: Determination of improved Cs2+(X) and Cs2(B) spectroscopic constants

NASA Astrophysics Data System (ADS)

Oldenburg, A. L.; John, P. C.; Eden, J. G.

2000-12-01

Vibrational wave packets in the B 1Πu and D 1Σu+ excited states of Cs2 have been studied on the ˜100 fs time scale by pump-probe laser spectroscopy. The temporal behavior of the wave packets was monitored by photoionizing the electronically excited molecule with a time-delayed probe pulse and recording the time and energy-integrated photoelectron signal as a function of time delay between the pump and probe pulses. For the B 1Σu+ experiments, wave packets were produced by exciting the B 1Σu+←X 1Σg+ transition in the ˜740-790 nm region and subsequently detected by photoionizing the molecule at wavelengths between 565 nm and 600 nm. By simulating the experimentally observed transients with the density matrix formalism (and explicitly accounting for laser chirp and |Δv|>1 coherences), improved values for the equilibrium internuclear separation for the Cs2(B1Πu) state and Te for the Cs2+(X) state were determined to be Re(B 1Πu)=4.93±0.03 Å and Te[Cs2+(X)]=29 930±100 cm-1, respectively. Similar experiments were conducted for the D 1Σu+ state. Wave packets composed of vibrational levels (v'≈40-50) perturbed by the bound 2 3Πou state were produced on the D 1Σu+ potential surface by driving the D 1Σu+←X 1Σg+ transition in the 575-610 nm spectral interval.

VUV spectroscopic study of the ? state of H2

NASA Astrophysics Data System (ADS)

Dickenson, G. D.; Ubachs, W.

2014-04-01

Spectral lines, probing rotational quantum states J‧ = 0, 1, 2 of the inner well vibrations (υ‧ ≤ 8) in the ? state of molecular hydrogen, were recorded in high resolution using a vacuum ultraviolet Fourier transform absorption spectrometer in the wavelength range 73-86 nm. Accurate line positions and predissociation widths are determined from a fit to the absorption spectra. Improved values for the line positions are obtained, while the predissociation widths agree well with previous investigations.

Analysis of femtosecond pump-probe photoelectron-photoion coincidence measurements applying Bayesian probability theory

NASA Astrophysics Data System (ADS)

Rumetshofer, M.; Heim, P.; Thaler, B.; Ernst, W. E.; Koch, M.; von der Linden, W.

2018-06-01

Ultrafast dynamical processes in photoexcited molecules can be observed with pump-probe measurements, in which information about the dynamics is obtained from the transient signal associated with the excited state. Background signals provoked by pump and/or probe pulses alone often obscure these excited-state signals. Simple subtraction of pump-only and/or probe-only measurements from the pump-probe measurement, as commonly applied, results in a degradation of the signal-to-noise ratio and, in the case of coincidence detection, the danger of overrated background subtraction. Coincidence measurements additionally suffer from false coincidences, requiring long data-acquisition times to keep erroneous signals at an acceptable level. Here we present a probabilistic approach based on Bayesian probability theory that overcomes these problems. For a pump-probe experiment with photoelectron-photoion coincidence detection, we reconstruct the interesting excited-state spectrum from pump-probe and pump-only measurements. This approach allows us to treat background and false coincidences consistently and on the same footing. We demonstrate that the Bayesian formalism has the following advantages over simple signal subtraction: (i) the signal-to-noise ratio is significantly increased, (ii) the pump-only contribution is not overestimated, (iii) false coincidences are excluded, (iv) prior knowledge, such as positivity, is consistently incorporated, (v) confidence intervals are provided for the reconstructed spectrum, and (vi) it is applicable to any experimental situation and noise statistics. Most importantly, by accounting for false coincidences, the Bayesian approach allows us to run experiments at higher ionization rates, resulting in a significant reduction of data acquisition times. The probabilistic approach is thoroughly scrutinized by challenging mock data. The application to pump-probe coincidence measurements on acetone molecules enables quantitative interpretations about the molecular decay dynamics and fragmentation behavior. All results underline the superiority of a consistent probabilistic approach over ad hoc estimations.

Differentiation of surface and bulk conductivities in topological insulator via four-probe spectroscopy

DOE PAGES

Zhang, Xiaoguang; McGuire, Michael A.; Chen, Yong P.; ...

2016-03-08

Topological insulators, with characteristic topological surface states, have emerged as a new state of matter with rich potentials for both fundamental physics and device applications. However, the experimental detection of the surface transport has been hampered by the unavoidable extrinsic conductivity associated with the bulk crystals. Here we show that a four-probe transport spectroscopy in a multi-probe scanning tunneling microscopy system can be used to differentiate conductivities from the surface states and the coexisting bulk states in topological insulators. We derive a scaling relation of measured resistance with respect to varying inter-probe spacing for two interconnected conduction channels, which allowsmore » quantitative determination of conductivities from both channels. Using this method, we demonstrate the separation of 2D and 3D conduction in topological insulators by comparing the conductance scaling of Bi 2Se 3, Bi 2Te 2Se, and Sb-doped Bi 2Se 3 with that of a pure 2D conductance of graphene on SiC substrate. We also report the 2D conductance enhancement due to the surface doping effect in topological insulators. This technique can be applied to reveal 2D to 3D crossover of conductance in other complex systems.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jana, Dipankar, E-mail: dip2602@gmail.com; Porwal, S.; Sharma, T. K., E-mail: tarun@rrcat.gov.in

Pump-probe Surface Photovoltage Spectroscopy (SPS) measurements are performed on semiconductor epitaxial layers. Here, an additional sub-bandgap cw pump laser beam is used in a conventional chopped light geometry SPS setup under the pump-probe configuration. The main role of pump laser beam is to saturate the sub-bandgap localized states whose contribution otherwise swamp the information related to the bandgap of material. It also affects the magnitude of Dember voltage in case of semi-insulating (SI) semiconductor substrates. Pump-probe SPS technique enables an accurate determination of the bandgap of semiconductor epitaxial layers even under the strong influence of localized sub-bandgap states. The pumpmore » beam is found to be very effective in suppressing the effect of surface/interface and bulk trap states. The overall magnitude of SPV signal is decided by the dependence of charge separation mechanisms on the intensity of the pump beam. On the contrary, an above bandgap cw pump laser can be used to distinguish the signatures of sub-bandgap states by suppressing the band edge related feature. Usefulness of the pump-probe SPS technique is established by unambiguously determining the bandgap of p-GaAs epitaxial layers grown on SI-GaAs substrates, SI-InP wafers, and p-GaN epilayers grown on Sapphire substrates.« less

Proton transfer mediated by the vibronic coupling in oxygen core ionized states of glyoxalmonoxime studied by infrared-X-ray pump-probe spectroscopy.

PubMed

Felicíssimo, V C; Guimarães, F F; Cesar, A; Gel'mukhanov, F; Agren, H

2006-11-30

The theory of IR-X-ray pump-probe spectroscopy beyond the Born-Oppenheimer approximation is developed and applied to the study of the dynamics of intramolecular proton transfer in glyoxalmonoxime leading to the formation of the tautomer 2-nitrosoethenol. Due to the IR pump pulses the molecule gains sufficient energy to promote a proton to a weakly bound well. A femtosecond X-ray pulse snapshots the wave packet route and, hence, the dynamics of the proton transfer. The glyoxalmonoxime molecule contains two chemically nonequivalent oxygen atoms that possess distinct roles in the hydrogen bond, a hydrogen donor and an acceptor. Core ionizations of these form two intersecting core-ionized states, the vibronic coupling between which along the OH stretching mode partially delocalizes the core hole, resulting in a hopping of the core hole from one site to another. This, in turn, affects the dynamics of the proton transfer in the core-ionized state. The quantum dynamical simulations of X-ray photoelectron spectra of glyoxalmonoxime driven by strong IR pulses demonstrate the general applicability of the technique for studies of intramolecular proton transfer in systems with vibronic coupling.

Probing Trapped Ion Energies Via Ion-Molecule Reaction Kinetics: Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

DTIC Science & Technology

1992-05-28

ORGANIZATION (if applicable) Office of Naval Research N00014-87- j - 1248 Bc. ADDRESS (City, State, and ZIP Code) 10. SOURCE OF FUNDING NUMBERS 800 N. Quincy St...RESEARCH Grant NOOO14-87- J -1248 R & T Code 4134052 TECHNICAL REPORT NO. 36 Probing Trapped Ion Energies Via Ion-Molecule Reaction Kinetics: Fourier...reactivity (for charge transfer with N2) of the higher energy J =1/2 state is approximately three times that of the J =3/2 state at collision energies

Conformation-Specific Infrared and Ultraviolet Spectroscopy of α-METHYLBENZYL Radical: Probing the State-Dependent Effects of Methyl Rocking against a Radical Site

NASA Astrophysics Data System (ADS)

Kidwell, Nathanael M.; Mehta, Deepali N.; Zwier, Timothy S.; Reilly, Neil J.; Kokkin, Damian L.; McCarthy, Michael C.

2012-06-01

Combustion processes involve a myriad of complex reaction pathways which connect smaller precursors to larger polyaromatic hydrocarbons, many of which are still unknown. In particular, benzyl-type radicals play an important role in combustible fuels due to their intrinsic resonance stabilization and consequent increase in relative concentration. Here, we present a study of the vibronic spectroscopy of α-Methylbenzyl radical (α-MeBz), in which the orientation of the methyl group adjacent to the radical site responds to the electronic interaction extending from the conjugated π-system. Probing the isolated radical, produced in an electrical discharge under jet-cooled conditions, the two-color resonant two-photon ionization, fluorescence excitation, and dispersed fluorescence spectra were obtained in order to determine the ground and excited state barriers to internal rotation and the angular change associated with electronic excitation. Resonant ion-dip infrared spectroscopy (RIDIRS) has also been implemented to elucidate the infrared signatures in the alkyl and aromatic CH stretch regions in order to probe in a complementary way the state-dependent conformational preferences of α-MeBz. We will show that the D0- and D1-RIDIR spectra report sensitively on the strong coupling between the CH stretch vibrations and the C_α-C_β torsional geometry. Furthermore, photoionization efficiency scans were carried out to reveal the adiabatic ionization threshold of α-MeBz and the quantized levels present in the radical cation state.

Formation of relief on Europa's surface and analysis of a melting probe movement through the ice

NASA Astrophysics Data System (ADS)

Erokhina, O. S.; Chumachenko, E. N.; Dunham, D. W.; Aksenov, S. A.; Logashina, I. V.

2013-12-01

These days, studies of planetary bodies' are of great interest. And of special interest are the icy moons of the giant planets like Jupiter and Saturn. Analysis of 'Voyager 1', 'Voyager 2', 'Galileo' and 'Cassini' spacecraft data showed that icy covers were observed on Jupiter's moons Ganymede, Europa and Calisto, and Saturn's moons Titan and Enceladus. Of particular interest is the relatively smooth surface of Europa. The entire surface is covered by a system of bands, valleys, and ridges. These structures are explained by the mobility of surface ice, and the impact of stress and large-scale tectonic processes. Also conditions on these moons allow speculation about possible life, considering these moons from an astrobiological point of view. To study the planetary icy body in future space missions, one of the problems to solve is the problem of design of a special device capable of penetrating through the ice, as well as the choice of the landing site of this probe. To select a possible landing site, analysis of Europa's surface relief formation is studied. This analysis showed that compression, extention, shearing, and bending can influence some arbitrarily separated section of Europe's icy surface. The computer simulation with the finite element method (FEM) was performed to see what types of defects could arise from such effects. The analysis showed that fractures and cracks could have various forms depending on the stress-strained state arising in their vicinity. Also the problem of a melting probe's movement through the ice is considered: How the probe will move in low gravity and low atmospheric pressure; whether the hole formed in the ice will be closed when the probe penetrates far enough or not; what is the influence of the probe's characteristics on the melting process; what would be the order of magnitude of the penetration velocity. This study explores the technique based on elasto-plastic theory and so-called 'solid water' theory to estimate the melting velocity and to study the melting process. Based on this technique, several cases of melting probe motion are considered, the velocity of the melting probe is estimated, the influence of different factors are studied and discussed, and an easy way to optimize the parameters of the probe is proposed.

Ionizable Nitroxides for Studying Local Electrostatic Properties of Lipid Bilayers and Protein Systems by EPR.

PubMed

Voinov, Maxim A; Smirnov, Alex I

2015-01-01

Electrostatic interactions are known to play a major role in the myriad of biochemical and biophysical processes. Here, we describe biophysical methods to probe local electrostatic potentials of proteins and lipid bilayer systems that are based on an observation of reversible protonation of nitroxides by electron paramagnetic resonance (EPR). Two types of probes are described: (1) methanethiosulfonate derivatives of protonatable nitroxides for highly specific covalent modification of the cysteine's sulfhydryl groups and (2) spin-labeled phospholipids with a protonatable nitroxide tethered to the polar head group. The probes of both types report on their ionization state through changes in magnetic parameters and degree of rotational averaging, thus, allowing the electrostatic contribution to the interfacial pKa of the nitroxide, and, therefore, the local electrostatic potential to be determined. Due to their small molecular volume, these probes cause a minimal perturbation to the protein or lipid system. Covalent attachment secures the position of the reporter nitroxides. Experimental procedures to characterize and calibrate these probes by EPR, and also the methods to analyze the EPR spectra by simulations are outlined. The ionizable nitroxide labels and the nitroxide-labeled phospholipids described so far cover an exceptionally wide range of ca. 2.5-7.0 pH units, making them suitable to study a broad range of biophysical phenomena, especially at the negatively charged lipid bilayer surfaces. The rationale for selecting proper electrostatically neutral interface for probe calibration, and examples of lipid bilayer surface potential studies, are also described. © 2015 Elsevier Inc. All rights reserved.

Scalar one-point functions and matrix product states of AdS/dCFT

NASA Astrophysics Data System (ADS)

de Leeuw, Marius; Kristjansen, Charlotte; Linardopoulos, Georgios

2018-06-01

We determine in a closed form all scalar one-point functions of the defect CFT dual to the D3-D5 probe brane system with k units of flux which amounts to calculating the overlap between a Bethe eigenstate of the integrable SO(6) spin chain and a certain matrix product state of bond dimension k. In particular, we show that the matrix product state is annihilated by all the parity odd charges of the spin chain which has recently been suggested as the criterion for such a state to correspond to an integrable initial state. Finally, we discuss the properties of the analogous matrix product state for the SO(5) symmetric D3-D7 probe brane set-up.

Tunneling spectroscopy of Majorana-Kondo devices

NASA Astrophysics Data System (ADS)

Eriksson, Erik; Nava, Andrea; Mora, Christophe; Egger, Reinhold

2014-12-01

We study the local density of states (LDOS) in systems of Luttinger-liquid nanowires connected to a common mesoscopic superconducting island, in which Majorana bound states give rise to different types of topological Kondo effects. We show that electron interactions enhance the low-energy LDOS in the leads close to the island, with unusual exponents due to Kondo physics that can be probed in tunneling experiments.

Low-control and robust quantum refrigerator and applications with electronic spins in diamond

NASA Astrophysics Data System (ADS)

Mohammady, M. Hamed; Choi, Hyeongrak; Trusheim, Matthew E.; Bayat, Abolfazl; Englund, Dirk; Omar, Yasser

2018-04-01

We propose a general protocol for low-control refrigeration and thermometry of thermal qubits, which can be implemented using electronic spins in diamond. The refrigeration is implemented by a probe, consisting of a network of interacting spins. The protocol involves two operations: (i) free evolution of the probe; and (ii) a swap gate between one spin in the probe and the thermal qubit we wish to cool. We show that if the initial state of the probe falls within a suitable range, and the free evolution of the probe is both unital and conserves the excitation in the z direction, then the cooling protocol will always succeed, with an efficiency that depends on the rate of spin dephasing and the swap-gate fidelity. Furthermore, measuring the probe after it has cooled many qubits provides an estimate of their temperature. We provide a specific example where the probe is a Heisenberg spin chain, and suggest a physical implementation using electronic spins in diamond. Here, the probe is constituted of nitrogen vacancy (NV) centers, while the thermal qubits are dark spins. By using a novel pulse sequence, a chain of NV centers can be made to evolve according to a Heisenberg Hamiltonian. This proposal allows for a range of applications, such as NV-based nuclear magnetic resonance of photosensitive molecules kept in a dark spot on a sample, and it opens up possibilities for the study of quantum thermodynamics, environment-assisted sensing, and many-body physics.

Time-resolved double resonance study of J- and K-changing rotational collisional processes in CH3Cl

NASA Astrophysics Data System (ADS)

Pape, Travis W.; De Lucia, Frank C.; Skatrud, David D.

1994-04-01

Time-resolved double resonance spectroscopy using infrared pump radiation and millimeter-wave and submillimeter-wave probe radiation (IRMMDR) has been used to study rotational energy transfer (RET) in CH3Cl. A collisional energy transfer model using only five parameters for RET plus those needed for vibrational processes is shown to accurately model 350 IRMMDR time responses for two different pump states and 43 probe transitions covering a wide range of rotational states. Previous studies in this laboratory have revealed that J- and K-changing RET have vastly different characters in CH3F [J. Chem. Phys. 92, 6480 (1990)]. Both J- and K-changing RET were accurately modeled with four parameters—one for dipole-dipole collisions, two for the ΔJ scaling law, and one for the cumulative rate of K-changing collisions. As was found for CH3F, J-changing rotational collision rates in CH3Cl are modeled accurately by both the statistical power gap (SPG) law and the infinite order sudden approximation using a power law expression for the basis rates (IOS-P). However, in contrast to CH3F, where all IRMMDR time responses for K-changing collisions have the same shape, many time responses of CH3Cl states populated by K-changing collisions contain an additional early time feature (ETF) that varies with pump and probe states. Nonetheless, a simple generalization of the previously reported model for K-changing collisions is shown to account for all of the additional features observed in CH3Cl. Rather than observing a fixed temperature for K-changing collisions as was the case for CH3F, the temperature is found to be a function of time for CH3Cl. Moreover, the two new parameters this adds to the RET model are related to known physical quantities. A qualitative argument of K-changing collisions based on a classical picture is offered to explain the difference between the measured J- and K-changing state-to-state rates in CH3Cl.

Confocal ultrafast pump-probe spectroscopy: a new technique to explore nanoscale composites.

PubMed

Virgili, Tersilla; Grancini, Giulia; Molotokaite, Egle; Suarez-Lopez, Inma; Rajendran, Sai Kiran; Liscio, Andrea; Palermo, Vincenzo; Lanzani, Guglielmo; Polli, Dario; Cerullo, Giulio

2012-04-07

This article is devoted to the exploration of the benefits of a new ultrafast confocal pump-probe technique, able to study the photophysics of different structured materials with nanoscale resolution. This tool offers many advantages over standard stationary microscopy techniques because it directly interrogates excited state dynamics in molecules, providing access to both radiative and non-radiative deactivation processes at a local scale. In this paper we present a few different examples of its application to organic semiconductor systems. The first two are focussed on the study of the photophysics of phase-separated polymer blends: (i) a blue-emitting polyfluorene (PFO) in an inert matrix of PMMA and (ii) an electron donor polythiophene (P3HT) mixed with an electron acceptor fullerene derivative (PCBM). The experimental results on these samples demonstrate the capability of the technique to unveil peculiar interfacial dynamics at the border region between phase-segregated domains, which would be otherwise averaged out using conventional pump-probe spectroscopy. The third example is the study of the photophysics of isolated mesoscopic crystals of the PCBM molecule. Our ultrafast microscope could evidence the presence of two distinctive regions within the crystals. In particular, we could pinpoint for the first time areas within the crystals showing photobleaching/stimulated emission signals from a charge-transfer state. This journal is © The Royal Society of Chemistry 2012

Investigation of space shuttle vehicle 140C configuration orbiter (model 16-0) wheel well pressure loads in the Rockwell International 7.75 x 11 foot wind tunnel (OA143)

NASA Technical Reports Server (NTRS)

Mennell, R. C.

1975-01-01

Experimental aerodynamic investigations were conducted on a sting mounted .0405-scale representation of the 140C outer mold line space shuttle orbiter configuration in the Rockwell International 7.75 x 11.00 foot low speed wind tunnel. The primary test objectives were to define the orbiter wheel well pressure loading and its effects on landing gear thermal insulation and to investigate the pressure environment experienced by both the horizontal flight nose probe and air vent door probes. Steady state and dynamic pressure values were recorded in the orbiter nose gear well, left main landing gear well, horizontal flight nose probe, and both left and right air vent door probe. All steady state pressure levels were measured by Statham differential pressure transducers while dynamic pressure levels were recorded by Kulite high frequency response pressure sensors.

Photoisomerization and photoionization of the photoactive yellow protein chromophore in solution.

PubMed

Larsen, Delmar S; Vengris, Mikas; van Stokkum, Ivo H M; van der Horst, Michael A; de Weerd, Frank L; Hellingwerf, Klaas J; van Grondelle, Rienk

2004-04-01

Dispersed pump-dump-probe spectroscopy has the ability to characterize and identify the underlying ultrafast dynamical processes in complicated chemical and biological systems. This technique builds on traditional pump-probe techniques by exploring both ground- and excited-state dynamics and characterizing the connectivity between constituent transient states. We have used the dispersed pump-dump-probe technique to investigate the ground-state dynamics and competing excited-state processes in the excitation-induced ultrafast dynamics of thiomethyl p-coumaric acid, a model chromophore for the photoreceptor photoactive yellow protein. Our results demonstrate the parallel formation of two relaxation pathways (with multiple transient states) that jointly lead to two different types of photochemistry: cis-trans isomerization and detachment of a hydrated electron. The relative transition rates and quantum yields of both pathways have been determined. We find that the relaxation of the photoexcited chromophores involves multiple, transient ground-state intermediates and the chromophore in solution does not generate persistent photoisomerized products, but instead undergoes photoionization resulting in the generation of detached electrons and radicals. These results are of great value in interpreting the more complex dynamical changes in the optical properties of the photoactive yellow protein.

Photoisomerization and Photoionization of the Photoactive Yellow Protein Chromophore in Solution

PubMed Central

Larsen, Delmar S.; Vengris, Mikas; van Stokkum, Ivo H. M.; van der Horst, Michael A.; de Weerd, Frank L.; Hellingwerf, Klaas J.; van Grondelle, Rienk

2004-01-01

Dispersed pump-dump-probe spectroscopy has the ability to characterize and identify the underlying ultrafast dynamical processes in complicated chemical and biological systems. This technique builds on traditional pump-probe techniques by exploring both ground- and excited-state dynamics and characterizing the connectivity between constituent transient states. We have used the dispersed pump-dump-probe technique to investigate the ground-state dynamics and competing excited-state processes in the excitation-induced ultrafast dynamics of thiomethyl p-coumaric acid, a model chromophore for the photoreceptor photoactive yellow protein. Our results demonstrate the parallel formation of two relaxation pathways (with multiple transient states) that jointly lead to two different types of photochemistry: cis-trans isomerization and detachment of a hydrated electron. The relative transition rates and quantum yields of both pathways have been determined. We find that the relaxation of the photoexcited chromophores involves multiple, transient ground-state intermediates and the chromophore in solution does not generate persistent photoisomerized products, but instead undergoes photoionization resulting in the generation of detached electrons and radicals. These results are of great value in interpreting the more complex dynamical changes in the optical properties of the photoactive yellow protein. PMID:15041690

Electromagnetic radiation as a probe of the initial state and of viscous dynamics in relativistic nuclear collisions

NASA Astrophysics Data System (ADS)

Vujanovic, Gojko; Paquet, Jean-François; Denicol, Gabriel S.; Luzum, Matthew; Jeon, Sangyong; Gale, Charles

2016-07-01

The penetrating nature of electromagnetic signals makes them suitable probes to explore the properties of the strongly interacting medium created in relativistic nuclear collisions. We examine the effects of the initial conditions and shear relaxation time on the spectra and flow coefficients of electromagnetic probes, using an event-by-event 3+1-dimensional viscous hydrodynamic simulation (music).

Radiopharmaceuticals in PET, Progress and Promise

DOE R&D Accomplishments Database

Wolf, A. P.; Fowler, J. S.

1988-11-01

It is the intention of this presentation to focus on the current state of radiopharmaceuticals for PET and where this is leading us. PET radiopharmaceuticals can be broken down into perhaps seven categories at present with each being applicable to a different aspect of human biochemistry. These are: metabolic probes, neurochemical probes, enzyme probes, ion channel blockers, blood flow agents, ethical drugs and other positron emitters.

A nonimaging scintillation probe to measure penile hemodynamics.

PubMed

Zuckier, L S; Korupolu, G R; Gladshteyn, M; Sattenberg, R; Goldstein, R; Ricciardi, R; Goodwin, P; Melman, A; Blaufox, M D

1995-12-01

We have developed a penile nonimaging scintillation (PNIS) probe consisting of a plastic well-type scintillation crystal interfaced to a portable computer and acquisition board. This report describes the design of the PNIS probe, performance characteristics, mode of usage and illustrative results which demonstrate its capabilities. With the PNIS probe, penile blood-pool studies were performed in nine patients utilizing 3.7 MBq (100 microCi) autologous 99mTc-labeled red blood cells (RBCs). Venous blood standards were assayed to enable conversion of the count rate to volummetric measurements. Washin of peripherally administered 99mTc-RBCs was mathematically analyzed to estimate penile blood volume and cavernosal flow rate in the flaccid state. The rate of change of penile blood volume after intracavernosal vasodilators was used to generate measures of stimulated flow. A major advantage of this device over the gamma-camera is a 3300-fold increase in count rate sensitivity, which allows for markedly improved temporal resolution while significantly reducing the radiopharmaceutical dosage. Additionally, the PNIS probe is portable, economical and is not dependent on operator-defined regions of interest. Count rate sensitivity is relatively constant within the bore, with the exception of the proximal region adjacent to the opening, where geometric efficiency is reduced. The PNIS probe is an effective device for measuring penile activity in radionuclide studies, allowing for acquisition of time-activity curves of the penis during flaccid washin of peripherally labeled red blood cells and after pharmacologic stimulation to induce erection.

Fast Open-World Person Re-Identification.

PubMed

Zhu, Xiatian; Wu, Botong; Huang, Dongcheng; Zheng, Wei-Shi

2018-05-01

Existing person re-identification (re-id) methods typically assume that: 1) any probe person is guaranteed to appear in the gallery target population during deployment (i.e., closed-world) and 2) the probe set contains only a limited number of people (i.e., small search scale). Both assumptions are artificial and breached in real-world applications, since the probe population in target people search can be extremely vast in practice due to the ambiguity of probe search space boundary. Therefore, it is unrealistic that any probe person is assumed as one target people, and a large-scale search in person images is inherently demanded. In this paper, we introduce a new person re-id search setting, called large scale open-world (LSOW) re-id, characterized by huge size probe images and open person population in search thus more close to practical deployments. Under LSOW, the under-studied problem of person re-id efficiency is essential in addition to that of commonly studied re-id accuracy. We, therefore, develop a novel fast person re-id method, called Cross-view Identity Correlation and vErification (X-ICE) hashing, for joint learning of cross-view identity representation binarisation and discrimination in a unified manner. Extensive comparative experiments on three large-scale benchmarks have been conducted to validate the superiority and advantages of the proposed X-ICE method over a wide range of the state-of-the-art hashing models, person re-id methods, and their combinations.

Photoionisation of molecular wavepackets - the NaK( C1Σ +) case

NASA Astrophysics Data System (ADS)

Andersson, Renée; Kadi, Malin; Davidsson, Jan; Hansson, Tony

2002-01-01

The ultrafast photoionisation dynamics of NaK molecules in the C(3) 1Σ + state is investigated by pump-probe spectroscopy. The results are consistent with decreasing electronic transition dipole moment for photoionisation of the C state with increasing internuclear separation, due to increasing Na +K - ion pair character of the C state at the outer turning point of the wavepacket trajectory. Effects of a possible low-lying superexcited state cannot be ruled out, though, and in general future studies on ultrafast photoionisation processes need to address in more detail such effects.

Quantum state-resolved probing of strong-field-ionized xenon atoms using femtosecond high-order harmonic transient absorption spectroscopy.

PubMed

Loh, Zhi-Heng; Khalil, Munira; Correa, Raoul E; Santra, Robin; Buth, Christian; Leone, Stephen R

2007-04-06

Femtosecond high-order harmonic transient absorption spectroscopy is used to resolve the complete |j,m quantum state distribution of Xe+ produced by optical strong-field ionization of Xe atoms at 800 nm. Probing at the Xe N4/5 edge yields a population distribution rhoj,|m| of rho3/2,1/2ratiorho1/2,1/2ratiorho3/2,3/2=75+/-6 :12+/-3 :13+/-6%. The result is compared to a tunnel ionization calculation with the inclusion of spin-orbit coupling, revealing nonadiabatic ionization behavior. The sub-50-fs time resolution paves the way for tabletop extreme ultraviolet absorption probing of ultrafast dynamics.

Study of clustering structures through breakup reactions

NASA Astrophysics Data System (ADS)

Capel, Pierre

2014-12-01

Models for the description of breakup reactions used to study the structure of exotic cluster structures like halos are reviewed. The sensitivity of these models to the projectile description is presented. Calculations are sensitive to the projectile ground state mostly through its asymptotic normalisation coefficient (ANC). They also probe the continuum of the projectile. This enables studying not only resonant states of the projectile but also its non-resonant continuum both resonant and non-resonant. This opens the possibility to study correlations between both halo neutrons in two-neutron halo nuclei.

Transient birefringence effects in electromagnetically induced transparency

NASA Astrophysics Data System (ADS)

Parshkov, O. M.

2015-11-01

We report the results of numerical modelling of transient birefringence that arises as a result of electromagnetically induced transparency on degenerate quantum transitions between the states with J = 0, 1 and 2 in the presence of the Doppler broadening of spectral lines. It is shown that in the case of a linearly polarised control field, the effect of transient birefringence leads to a decay of the input circularly polarised probe pulse into separate linearly polarised pulses inside a medium. In the case of a circularly polarised control field, the effect of transient birefringence manifests itself in a decay of the input linearly polarised probe pulse into separate circularly polarised pulses. It is shown that the distance that a probe pulse has to pass in a medium before decaying into subpulses is considerably greater in the first case than in the second. The influence of the input probe pulse power and duration on the process of spatial separation into individual pulses inside a medium is studied. A qualitative analysis of the obtained results is presented.

Perforated cenosphere-supported pH-sensitive spin probes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fomenko, E.V.; Bobko, A.A.; Salanov, A.N.

2008-03-15

Porous supports with an accessible internal volume and a shell providing the diffusive migration of pH-sensitive spin probes were obtained for the first time from hollow aluminosilicate cenospheres isolated from the coal fly ash. Using the methods of scanning electron microscopy and electron spin resonance, the morphology of different porous cenosphere modifications and its influence on the diffusion of spin probes from the internal volume were studied. When supporting aqueous solutions of a radical, the characteristic diffusion time for the mesoporous structure of the support is longer by a factor of 3-5 than that for the macroporous structure. Ferrospinel inmore » a content of 6 wt.% do not virtually affect the diffusion rate of spin probes. A constant rate of radical migration of similar to 1 {mu} mol min{sup -1}, determined by radical solubility in water, is achieved when a radical in the solid aggregate state is supported on the magnetic cenospheres.« less

Nanometer scale composition study of MBE grown BGaN performed by atom probe tomography

NASA Astrophysics Data System (ADS)

Bonef, Bastien; Cramer, Richard; Speck, James S.

2017-06-01

Laser assisted atom probe tomography is used to characterize the alloy distribution in BGaN. The effect of the evaporation conditions applied on the atom probe specimens on the mass spectrum and the quantification of the III site atoms is first evaluated. The evolution of the Ga++/Ga+ charge state ratio is used to monitor the strength of the applied field. Experiments revealed that applying high electric fields on the specimen results in the loss of gallium atoms, leading to the over-estimation of boron concentration. Moreover, spatial analysis of the surface field revealed a significant loss of atoms at the center of the specimen where high fields are applied. A good agreement between X-ray diffraction and atom probe tomography concentration measurements is obtained when low fields are applied on the tip. A random distribution of boron in the BGaN layer grown by molecular beam epitaxy is obtained by performing accurate and site specific statistical distribution analysis.

Population trapping in the excited states using vacuum-induced coherence and adiabatic process

NASA Astrophysics Data System (ADS)

Lal Kumawat, Babu; Kumar, Pardeep; Dasgupta, Shubhrangshu

2018-02-01

We theoretically investigate how population can be trapped in the closely spaced excited levels in presence of vacuum-induced coherence (VIC). We employ delayed pulses to transfer population from a meta-stable state to the excited states. Subsequently, spontaneous emission from these excited states builds coherence between them. This coherence can be probed by using chirping, which leads to the decoupling of the excited states from the ground state thereby ensuring population transfer via delayed pulses. Our results indicate that the existence of VIC leads to the generation of a mixed state in the excited state manifold, where trapping of the population occurs even in the presence of large decay. This trapping may be realized in molecular systems and can be interpreted as a sensitive probe of VIC. We present suitable numerical analysis to support our results.

Quantitative dual-probe microdialysis: mathematical model and analysis.

PubMed

Chen, Kevin C; Höistad, Malin; Kehr, Jan; Fuxe, Kjell; Nicholson, Charles

2002-04-01

Steady-state microdialysis is a widely used technique to monitor the concentration changes and distributions of substances in tissues. To obtain more information about brain tissue properties from microdialysis, a dual-probe approach was applied to infuse and sample the radiotracer, [3H]mannitol, simultaneously both in agar gel and in the rat striatum. Because the molecules released by one probe and collected by the other must diffuse through the interstitial space, the concentration profile exhibits dynamic behavior that permits the assessment of the diffusion characteristics in the brain extracellular space and the clearance characteristics. In this paper a mathematical model for dual-probe microdialysis was developed to study brain interstitial diffusion and clearance processes. Theoretical expressions for the spatial distribution of the infused tracer in the brain extracellular space and the temporal concentration at the probe outlet were derived. A fitting program was developed using the simplex algorithm, which finds local minima of the standard deviations between experiments and theory by adjusting the relevant parameters. The theoretical curves accurately fitted the experimental data and generated realistic diffusion parameters, implying that the mathematical model is capable of predicting the interstitial diffusion behavior of [3H]mannitol and that it will be a valuable quantitative tool in dual-probe microdialysis.

Ionizable Nitroxides for Studying Local Electrostatic Properties of Lipid Bilayers and Protein Systems by EPR

PubMed Central

Voinov, Maxim A.; Smirnov, Alex I.

2016-01-01

Electrostatic interactions are known to play one of the major roles in the myriad of biochemical and biophysical processes. In this Chapter we describe biophysical methods to probe local electrostatic potentials of proteins and lipid bilayer systems that is based on an observation of reversible protonation of nitroxides by EPR. Two types of the electrostatic probes are discussed. The first one includes methanethiosulfonate derivatives of protonatable nitroxides that could be used for highly specific covalent modification of the cysteine’s sulfhydryl groups. Such spin labels are very similar in magnetic parameters and chemical properties to conventional MTSL making them suitable for studying local electrostatic properties of protein-lipid interfaces. The second type of EPR probes is designed as spin-labeled phospholipids having a protonatable nitroxide tethered to the polar head group. The probes of both types report on their ionization state through changes in magnetic parameters and a degree of rotational averaging, thus, allowing one to determine the electrostatic contribution to the interfacial pKa of the nitroxide, and, therefore, determining the local electrostatic potential. Due to their small molecular volume these probes cause a minimal perturbation to the protein or lipid system while covalent attachment secure the position of the reporter nitroxides. Experimental procedures to characterize and calibrate these probes by EPR and also the methods to analyze the EPR spectra by least-squares simulations are also outlined. The ionizable nitroxide labels and the nitroxide-labeled phospholipids described so far cover an exceptionally wide pH range from ca. 2.5 to 7.0 pH units making them suitable to study a broad range of biophysical phenomena especially at the negatively charged lipid bilayer surfaces. The rationale for selecting proper electrostatically neutral interface for calibrating such probes and example of studying surface potential of lipid bilayer is also described. PMID:26477252

Thermoelectric properties of the unfilled skutterudite FeSb 3 from first principles and Seebeck local probes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lemal, Sébastien; Nguyen, Ngoc; de Boor, Johannes

2015-11-16

In this paper, using a combination of first-principles calculations and experimental transport measurements, we study the electronic and magnetic structure of the unfilled skutterudite FeSb 3. We employ the hybrid functional approach for exchange correlation. The ground state is determined to be antiferromagnetic with an atomic magnetic moment of 1.6μ B/Fe. The Néel temperature T N is estimated at 6 K, in agreement with experiments which found a paramagnetic state down to 10 K. The ground state is semiconducting, with a small electronic gap of 33meV, also consistent with previous experiments on films. Charge carrier concentrations are estimated from Hallmore » resistance measurements. The Seebeck coefficient is measured and mapped using a scanning probe at room temperature that yields an average value of 38.6μVK -1, slightly lower than the theoretical result. Finally, the theoretical conductivity is analyzed as a function of temperature and concentration of charge carriers.« less

Scanning tunneling spectroscopy of molecular thin films and semiconductor nanostructures

NASA Astrophysics Data System (ADS)

Gaan, Sandeep

Work presented in this thesis mostly deals with nano-scale study of electronic properties of organic semiconducting molecules using pentacene (Pn) as a model system and compared with various SiC surfaces to gain more insight into physical processes at nano-scale. In addition, InAs quantum dots (QDs) in a GaAs matrix are studied to probe electronic states of individual QDs. Scanning tunneling microscopy (STM) and spectroscopy (STS) are the primary experimental techniques used to probe local electronic properties on the nano-scale. Vacuum sublimated Pn thin films were deposited onto SiC substrates for STM/STS experiments. STM studies show high quality ordered Pn films. Atomic force microscopy (AFM) images reveal dendritic growth pattern of these films. Local density of states (LDOS) measurements using STS reveals a HOMO-LUMO bandgap. In order to study charge transport properties of Pn films, different amount of charge were injected into the sample by systematically changing the tip-sample separation. Saturation of the tunnel current was observed at positive sample voltages (LUMO states). This effect was attributed to a transport/space charge limitation in tunnel current by treating it as a situation analogous to charge injection into insulators which gives rise to space charge limited current (also previously observed in the case of organic semiconductors). Using a simple model we were able to derive a hopping rate that characterizes nano-scale transport in Pn films at least in the vicinity of the STM probe-tip. We have studied effect of transport limitation in the tunnel current for various semiconductor surfaces. In order to probe surfaces of varying conductivities, we have used Si-rich SiC surfaces such as 3x3 and 3x3 -R30° (both Mott-Hubbard insulators) as well as a highly conducting C-rich graphene surface, and compared those results with the data obtained from Pn. We observe variation of the decay constant kappa (which characterizes the tunneling process) on these surfaces of varying conductivities. The graphene surface shows no transport limitation in the tunnel current, as evidenced by only small changes in kappa as a function of tunnel current for these surfaces. This result is in sharp contrast to the case of Pn where kappa rapidly decays to zero with increasing tunnel current due to transport/space charge limited effects in the semiconductor. Thus, the change is kappa value in STM experiments is reflective of non-ideal behavior of the tunneling. As a specific case of transport limitation on the nano-scale we have also studied InAs QDs grown in a GaAs matrix. We observe that the occupation of discrete quantized states in the dots with electrons has a significant effect on tunneling spectra. When the QD state is occupied by an electron the potential in the dot is modified such that this state does not contribute to the tunnel current. The state then remains "invisible" in the tunneling spectra. Only in presence of transport channels in the vicinity of the dots can the electron localized in the QD state leak out to the substrate, and only then does the state appears in the spectrum. In our experiments these transport channels arise from steps which form as a result of in situ cleaving process for cross-sectional STM (XSTM) measurements.

Ionosphere Plasma State Determination in Low Earth Orbit from International Space Station Plasma Monitor

NASA Technical Reports Server (NTRS)

Kramer, Leonard

2014-01-01

A plasma diagnostic package is deployed on the International Space Station (ISS). The system - a Floating Potential Measurement Unit (FPMU) - is used by NASA to monitor the electrical floating potential of the vehicle to assure astronaut safety during extravehicular activity. However, data from the unit also reflects the ionosphere state and seems to represent an unutilized scientific resource in the form of an archive of scientific plasma state data. The unit comprises a Floating Potential probe and two Langmuir probes. There is also an unused but active plasma impedance probe. The data, at one second cadence, are collected, typically for a two week period surrounding extravehicular activity events. Data is also collected any time a visiting vehicle docks with ISS and also when any large solar events occur. The telemetry system is unusual because the package is mounted on a television camera stanchion and its data is impressed on a video signal that is transmitted to the ground and streamed by internet to two off center laboratory locations. The data quality has in the past been challenged by weaknesses in the integrated ground station and distribution systems. These issues, since mid-2010, have been largely resolved and the ground stations have been upgraded. Downstream data reduction has been developed using physics based modeling of the electron and ion collecting character in the plasma. Recursive algorithms determine plasma density and temperature from the raw Langmuir probe current voltage sweeps and this is made available in real time for situational awareness. The purpose of this paper is to describe and record the algorithm for data reduction and to show that the Floating probe and Langmuir probes are capable of providing long term plasma state measurement in the ionosphere. Geophysical features such as the Appleton anomaly and high latitude modulation at the edge of the Auroral zones are regularly observed in the nearly circular, 51 deg inclined, 400 km altitude ISS orbit. Evidence of waves in the ion collection current data is seen in geographic zones known to exhibit the spread-F phenomenon. An anomaly in the current collection characteristic of the cylindrical probe appears also too be organized by the geomagnetic field.

Real-time detection of S(1D2) photofragments produced from the 1B2(1Σu+) state of CS2 by vacuum ultraviolet photoelectron imaging using 133 nm probe pulses

NASA Astrophysics Data System (ADS)

Horio, Takuya; Spesyvtsev, Roman; Furumido, Yu; Suzuki, Toshinori

2017-07-01

Ultrafast photodissociation dynamics from the 1B2(1Σu+) state of CS2 are studied by time-resolved photoelectron imaging using the fourth (4ω, 198 nm) and sixth (6ω, 133 nm) harmonics of a femtosecond Ti:sapphire laser. The 1B2 state of CS2 was prepared with the 4ω pulses, and subsequent dynamics were probed using the 6ω vacuum ultraviolet (VUV) pulses. The VUV pulses enabled real-time detection of S(1D2) photofragments, produced via CS2*(1B2(1Σu+)) → CS(X 1Σ+) + S(1D2). The photoionization signal of dissociating CS2*(1B2(1Σu+)) molecules starts to decrease at about 100 fs, while the S(1D2) fragments appear with a finite (ca. 400 fs) delay time after the pump pulse. Also discussed is the configuration interaction of the 1B2(1Σu+) state based on relative photoionization cross-sections to different cationic states.

Creating Rydberg electron wave packets using terahertz pulses

NASA Astrophysics Data System (ADS)

Bromage, Jake

1999-10-01

In this thesis I present experiments in which we excited classical-limit states of an atom using terahertz pulses. In a classical-limit state, an atom's outer electron is confined to a wave packet that orbits the core along a classical trajectory. Researchers have excited states with classical traits, but wave packets localized in all three dimensions have proved elusive. Theoretical studies have shown such states can be created using terahertz pulses. Using these techniques, we created a linear-orbit wave packet (LOWP), that is three-dimensionally localized and orbits along a line on one side of the atom's core. Terahertz pulses are sub-picosecond bursts of far- infrared radiation. Unlike ultrashort optical pulses, the electric field of terahertz pulses barely completes a single cycle. Our simulations of the atom-pulse interaction show that this electric field profile is critical in determining the quality of the wave packet. To characterize our terahertz pulses, we invented dithered-edge sampling which time- resolves the electric field using a photoconductive receiver and a triggered attenuator. We also studied how pulses are distorted after propagating through metallic structures, and used our findings to design our atomic experiments. We excited wave packets in atomic sodium using a two-step process. First, we used tunable, nanosecond dye lasers to excite an extreme Stark state. Next, we used a terahertz pump pulse to coherently redistribute population among extreme Stark states in neighboring manifolds. Interference between the final states produces a localized, dynamic LOWP. To analyze the LOWP, we ionized it with a stronger terahertz probe pulse, varying the pump-probe delay to map out its motion. We observed two strong LOWP signatures. Changing the static electric field produced small changes (2%) in the orbital period that agreed with our theoretical predictions. Secondly, because the LOWP scatters off the core, the pump-probe signal depended on the direction of the kick the LOWP received from the robe pulse. These observations, combined with our detailed simulations that used sodium parameters and the actual shape of the terahertz pulse, lead us to conclude that we excited a LOWP.

Observation of Topological Links Associated with Hopf Insulators in a Solid-State Quantum Simulator

NASA Astrophysics Data System (ADS)

Yuan, X.-X.; He, L.; Wang, S.-T.; Deng, D.-L.; Wang, F.; Lian, W.-Q.; Wang, X.; Zhang, C.-H.; Zhang, H.-L.; Chang, X.-Y.; Duan, L.-M.

2017-06-01

Hopf insulators are intriguing three-dimensional topological insulators characterized by an integer topological invariant. They originate from the mathematical theory of Hopf fibration and epitomize the deep connection between knot theory and topological phases of matter, which distinguishes them from other classes of topological insulators. Here, we implement a model Hamiltonian for Hopf insulators in a solid-state quantum simulator and report the first experimental observation of their topological properties, including fascinating topological links associated with the Hopf fibration and the integer-valued topological invariant obtained from a direct tomographic measurement. Our observation of topological links and Hopf fibration in a quantum simulator opens the door to probe rich topological properties of Hopf insulators in experiments. The quantum simulation and probing methods are also applicable to the study of other intricate three-dimensional topological model Hamiltonians.

The methyl- and aza-substituent effects on nonradiative decay mechanisms of uracil in water: a transient absorption study in the UV region.

PubMed

Hua, XinZhong; Hua, LinQiang; Liu, XiaoJun

2016-05-18

The nonradiative decay dynamics of photo-excited uracil (Ura) and its derivatives, i.e., thymine (5-methyluracil, Thy), 6-methyluracil (6-MU) and 6-azauracil (6-AU) in water, has been studied using a femtosecond transient absorption method. The molecules are populated in the lowest (1)ππ* state by a pump pulse at 266 nm, and a broadband continuum in the deep UV region is then employed as the probe. The extension of the continuous UV probe down to 250 nm enables us to investigate comprehensively the population dynamics of the ground states for those molecules and to uncover the substituent effects on nonradiative decay dynamics of uracil. Vibrational cooling in the ground states of Ura, Thy and 6-MU has been directly observed for the first time, providing solid evidence of the ultrafast (1)ππ* → S0 decay. In combination with the ground state bleaching signals, it is consolidated that their lowest (1)ππ* state decays via two parallel pathways, i.e., (1)ππ* → S0 and (1)ππ* → (1)nπ*. Moreover, the contribution of the (1)ππ* → (1)nπ* channel is found to be much smaller for Thy or 6-MU than for Ura. Different from methyl-substitution, the initial (1)ππ* state of the aza-substituent 6-AU decays primarily to the (1)nπ* state, while the (1)ππ* → S0 channel can be negligible. Our study provides a comprehensive understanding of the substituent effects on the excited-state dynamics of uracil in water.

High-pressure studies with x-rays using diamond anvil cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shen, Guoyin; Mao, Ho Kwang

2016-11-22

Pressure profoundly alters all states of matter. The symbiotic development of ultrahigh-pressure diamond anvil cells, to compress samples to sustainable multi-megabar pressures; and synchrotron x-ray techniques, to probe materials' properties in situ, has enabled the exploration of rich high-pressure (HP) science. In this article, we first introduce the essential concept of diamond anvil cell technology, together with recent developments and its integration with other extreme environments. We then provide an overview of the latest developments in HP synchrotron techniques, their applications, and current problems, followed by a discussion of HP scientific studies using x-rays in the key multidisciplinary fields. Thesemore » HP studies include: HP x-ray emission spectroscopy, which provides information on the filled electronic states of HP samples; HP x-ray Raman spectroscopy, which probes the HP chemical bonding changes of light elements; HP electronic inelastic x-ray scattering spectroscopy, which accesses high energy electronic phenomena, including electronic band structure, Fermi surface, excitons, plasmons, and their dispersions; HP resonant inelastic x-ray scattering spectroscopy, which probes shallow core excitations, multiplet structures, and spin-resolved electronic structure; HP nuclear resonant x-ray spectroscopy, which provides phonon densities of state and time-resolved Mössbauer information; HP x-ray imaging, which provides information on hierarchical structures, dynamic processes, and internal strains; HP x-ray diffraction, which determines the fundamental structures and densities of single-crystal, polycrystalline, nanocrystalline, and non-crystalline materials; and HP radial x-ray diffraction, which yields deviatoric, elastic and rheological information. Integrating these tools with hydrostatic or uniaxial pressure media, laser and resistive heating, and cryogenic cooling, has enabled investigations of the structural, vibrational, electronic, and magnetic properties of materials over a wide range of pressure-temperature conditions.« less

High-pressure studies with x-rays using diamond anvil cells

NASA Astrophysics Data System (ADS)

Shen, Guoyin; Mao, Ho Kwang

2017-01-01

Pressure profoundly alters all states of matter. The symbiotic development of ultrahigh-pressure diamond anvil cells, to compress samples to sustainable multi-megabar pressures; and synchrotron x-ray techniques, to probe materials’ properties in situ, has enabled the exploration of rich high-pressure (HP) science. In this article, we first introduce the essential concept of diamond anvil cell technology, together with recent developments and its integration with other extreme environments. We then provide an overview of the latest developments in HP synchrotron techniques, their applications, and current problems, followed by a discussion of HP scientific studies using x-rays in the key multidisciplinary fields. These HP studies include: HP x-ray emission spectroscopy, which provides information on the filled electronic states of HP samples; HP x-ray Raman spectroscopy, which probes the HP chemical bonding changes of light elements; HP electronic inelastic x-ray scattering spectroscopy, which accesses high energy electronic phenomena, including electronic band structure, Fermi surface, excitons, plasmons, and their dispersions; HP resonant inelastic x-ray scattering spectroscopy, which probes shallow core excitations, multiplet structures, and spin-resolved electronic structure; HP nuclear resonant x-ray spectroscopy, which provides phonon densities of state and time-resolved Mössbauer information; HP x-ray imaging, which provides information on hierarchical structures, dynamic processes, and internal strains; HP x-ray diffraction, which determines the fundamental structures and densities of single-crystal, polycrystalline, nanocrystalline, and non-crystalline materials; and HP radial x-ray diffraction, which yields deviatoric, elastic and rheological information. Integrating these tools with hydrostatic or uniaxial pressure media, laser and resistive heating, and cryogenic cooling, has enabled investigations of the structural, vibrational, electronic, and magnetic properties of materials over a wide range of pressure-temperature conditions.

Model-independent analysis of the orientation of fluorescent probes with restricted mobility in muscle fibers.

PubMed Central

Dale, R E; Hopkins, S C; an der Heide, U A; Marszałek, T; Irving, M; Goldman, Y E

1999-01-01

The orientation of proteins in ordered biological samples can be investigated using steady-state polarized fluorescence from probes conjugated to the protein. A general limitation of this approach is that the probes typically exhibit rapid orientational motion ("wobble") with respect to the protein backbone. Here we present a method for characterizing the extent of this wobble and for removing its effects from the available information about the static orientational distribution of the probes. The analysis depends on four assumptions: 1) the probe wobble is fast compared with the nanosecond time scale of its excited-state decay; 2) the orientational distributions of the absorption and emission transition dipole moments are cylindrically symmetrical about a common axis c fixed in the protein; 3) protein motions are negligible during the excited-state decay; 4) the distribution of c is cylindrically symmetrical about the director of the experimental sample. In a muscle fiber, the director is the fiber axis, F. All of the information on the orientational order of the probe that is available from measurements of linearly polarized fluorescence is contained in five independent polarized fluorescence intensities measured with excitation and emission polarizers parallel or perpendicular to F and with the propagation axis of the detected fluorescence parallel or perpendicular to that of the excitation. The analysis then yields the average second-rank and fourth-rank order parameters ( and ) of the angular distribution of c relative to F, and and , the average second-rank order parameters of the angular distribution for wobble of the absorption and emission transition dipole moments relative to c. The method can also be applied to other cylindrically ordered systems such as oriented lipid bilayer membranes and to processes slower than fluorescence that may be observed using longer-lived optically excited states. PMID:10049341

Proceedings: Outer Planet Probe Technology Workshop, summary volume

NASA Technical Reports Server (NTRS)

1974-01-01

A summary report and overview of the Outer Planet Probe Technology Conference are given. Summary data cover: (1) state of the art concerning mission definitions, probe requirements, systems, subsystems, and mission peculiar hardware, (2) mission and equipment trade-offs associated with Saturn/Uranus baseline configuration and the influence of Titan and Jupiter options on mission performance and costs, and (3) identification of critically required future R and D activities.

Phase-dependent above-barrier ionization of excited-state electrons.

PubMed

Yang, Weifeng; Song, Xiaohong; Chen, Zhangjin

2012-05-21

The carrier-envelope phase (CEP)-dependent above-barrier ionization (ABI) has been investigated in order to probe the bound-state electron dynamics. It is found that when the system is initially prepared in the excited state, the ionization yield asymmetry between left and right sides can occur both in low-energy and high-energy parts of the photoelectron spectra. Moreover, in electron momentum map, a new interference effect along the direction perpendicular to the laser polarization is found. We show that this interference is related to the competition among different excited states. The interference effect is dependent on CEPs of few-cycle probe pulses, which can be used to trace the superposition information and control the electron wave packet of low excited states.

Spin liquid state in the 3D frustrated antiferromagnet PbCuTe 2 O 6 : NMR and muon spin relaxation studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khuntia, P.; Bert, F.; Mendels, P.

In this study, PbCuTe 2O 6 is a rare example of a spin liquid candidate featuring a three-dimensional magnetic lattice. Strong geometric frustration arises from the dominant antiferromagnetic interaction that generates a hyperkagome network of Cu 2+ ions although additional interactions enhance the magnetic lattice connectivity. Through a combination of magnetization measurements and local probe investigations by NMR and muon spin relaxation down to 20 mK, we provide robust evidence for the absence of magnetic freezing in the ground state. The local spin susceptibility probed by the NMR shift hardly deviates from the macroscopic one down to 1 K pointingmore » to a homogeneous magnetic system with a low defect concentration. The saturation of the NMR shift and the sublinear power law temperature (T) evolution of the 1/T 1 NMR relaxation rate at low T point to a nonsinglet ground state favoring a gapless fermionic description of the magnetic excitations. Below 1 K a pronounced slowing down of the spin dynamics is witnessed, which may signal a reconstruction of spinon Fermi surface. Nonetheless, the compound remains in a fluctuating spin liquid state down to the lowest temperature of the present investigation.« less

Spin liquid state in the 3D frustrated antiferromagnet PbCuTe 2 O 6 : NMR and muon spin relaxation studies

DOE PAGES

Khuntia, P.; Bert, F.; Mendels, P.; ...

2016-03-11

In this study, PbCuTe 2O 6 is a rare example of a spin liquid candidate featuring a three-dimensional magnetic lattice. Strong geometric frustration arises from the dominant antiferromagnetic interaction that generates a hyperkagome network of Cu 2+ ions although additional interactions enhance the magnetic lattice connectivity. Through a combination of magnetization measurements and local probe investigations by NMR and muon spin relaxation down to 20 mK, we provide robust evidence for the absence of magnetic freezing in the ground state. The local spin susceptibility probed by the NMR shift hardly deviates from the macroscopic one down to 1 K pointingmore » to a homogeneous magnetic system with a low defect concentration. The saturation of the NMR shift and the sublinear power law temperature (T) evolution of the 1/T 1 NMR relaxation rate at low T point to a nonsinglet ground state favoring a gapless fermionic description of the magnetic excitations. Below 1 K a pronounced slowing down of the spin dynamics is witnessed, which may signal a reconstruction of spinon Fermi surface. Nonetheless, the compound remains in a fluctuating spin liquid state down to the lowest temperature of the present investigation.« less

Studies of rotationally inelastic collisions of NaK and NaCs with Ar and He perturbers

NASA Astrophysics Data System (ADS)

Jones, J.; Faust, C.; Richter, K.; Wolfe, C. M.; Ashman, S.; Malenda, R. F.; Weiser, P.; Carlus, S.; Fragale, A.; Hickman, A. P.; Huennekens, J.

2013-05-01

We report studies of rotationally inelastic collisions of Ar and He atoms with the molecules NaK and NaCs prepared in various ro-vibrational levels of the A1Σ+ electronic state. We use laser induced fluorescence (LIF) and polarization labeling (PL) spectroscopy in a pump-probe, two step excitation process. The pump excites the molecule to a ro-vibrational level (v , J) in the A state. The probe laser is scanned over transitions to the 31 Π state in NaK or the 53 Π state in NaCs. In addition to strong direct lines, we observe weak satellite lines that arise from collision-induced transitions of the A state level (v , J) to (v , J + ΔJ) . The ratio of intensities of the satellite line to the direct line in LIF and PL yields information about population and orientation transfer. Preliminary results show a strong propensity for collisions with ΔJ =even for NaK; the propensity is larger for He than for Ar. Collisions of NaCs with He show a similar propensity, but collisions of NaCs with Ar do not. Theoretical calculations are also underway. For He-NaK, we have completed potential surface calculations using GAMESS and coupled channel scattering calculations of rotational energy transfer and transfer of orientation. Work supported by NSF and XSEDE.

Simultaneous observations of electromagnetically induced transparency (EIT) and absorption (EIA) in a multi-level V-type system of 87Rb and theoretical simulation of the observed spectra using a multi-mode approach

NASA Astrophysics Data System (ADS)

Das, Bankim Chandra; Bhattacharyya, Dipankar; Das, Arpita; Chakrabarti, Shrabana; De, Sankar

2016-12-01

We report here simultaneous experimental observation of Electromagnetically Induced Transparency (EIT) and Electromagnetically Induced Absorption (EIA) in a multi-level V-type system in D2 transition of 87Rb, i.e., F =2 →F' with a strong pump and a weak probe beam. We studied the probe spectrum by locking the probe beam to the transition F =2 →F'=2 while the pump is scanned from F =2 →F' . EIA is observed for the open transition (F =2 →F'=2 ) whereas EIT is observed in the closed transition (F =2 →F'=3 ). Sub natural line-width is observed for the EIA. To simulate the observed spectra theoretically, Liouville equation for the three-level V-type system is solved analytically with a multi-mode approach for the density matrix elements. We assumed both the pump and the probe beams can couple the excited states. A multi-mode approach for the coherence terms facilitates the study of all the frequency contributions due to the pump and the probe fields. Since the terms contain higher harmonics of the pump and the probe frequencies, we expressed them in Fourier transformed forms. To simulate the probe spectrum, we have solved inhomogeneous difference equations for the coherence terms using the Green's function technique and continued fraction theory. The experimental line-widths of the EIT and the EIA are compared with our theoretical model. Our system can be useful in optical switching applications as it can be precisely tuned to render the medium opaque and transparent simultaneously.

Simultaneous observations of electromagnetically induced transparency (EIT) and absorption (EIA) in a multi-level V-type system of 87Rb and theoretical simulation of the observed spectra using a multi-mode approach.

PubMed

Das, Bankim Chandra; Bhattacharyya, Dipankar; Das, Arpita; Chakrabarti, Shrabana; De, Sankar

2016-12-14

We report here simultaneous experimental observation of Electromagnetically Induced Transparency (EIT) and Electromagnetically Induced Absorption (EIA) in a multi-level V-type system in D 2 transition of Rb87, i.e., F=2→F ' with a strong pump and a weak probe beam. We studied the probe spectrum by locking the probe beam to the transition F=2→F ' =2 while the pump is scanned from F=2→F ' . EIA is observed for the open transition (F=2→F ' =2) whereas EIT is observed in the closed transition (F=2→F ' =3). Sub natural line-width is observed for the EIA. To simulate the observed spectra theoretically, Liouville equation for the three-level V-type system is solved analytically with a multi-mode approach for the density matrix elements. We assumed both the pump and the probe beams can couple the excited states. A multi-mode approach for the coherence terms facilitates the study of all the frequency contributions due to the pump and the probe fields. Since the terms contain higher harmonics of the pump and the probe frequencies, we expressed them in Fourier transformed forms. To simulate the probe spectrum, we have solved inhomogeneous difference equations for the coherence terms using the Green's function technique and continued fraction theory. The experimental line-widths of the EIT and the EIA are compared with our theoretical model. Our system can be useful in optical switching applications as it can be precisely tuned to render the medium opaque and transparent simultaneously.

Vertical wind velocity measurements using a five-hole probe with remotely piloted aircraft to study aerosol-cloud interactions

NASA Astrophysics Data System (ADS)

Calmer, Radiance; Roberts, Gregory C.; Preissler, Jana; Sanchez, Kevin J.; Derrien, Solène; O'Dowd, Colin

2018-05-01

The importance of vertical wind velocities (in particular positive vertical wind velocities or updrafts) in atmospheric science has motivated the need to deploy multi-hole probes developed for manned aircraft in small remotely piloted aircraft (RPA). In atmospheric research, lightweight RPAs ( < 2.5 kg) are now able to accurately measure atmospheric wind vectors, even in a cloud, which provides essential observing tools for understanding aerosol-cloud interactions. The European project BACCHUS (impact of Biogenic versus Anthropogenic emissions on Clouds and Climate: towards a Holistic UnderStanding) focuses on these specific interactions. In particular, vertical wind velocity at cloud base is a key parameter for studying aerosol-cloud interactions. To measure the three components of wind, a RPA is equipped with a five-hole probe, pressure sensors, and an inertial navigation system (INS). The five-hole probe is calibrated on a multi-axis platform, and the probe-INS system is validated in a wind tunnel. Once mounted on a RPA, power spectral density (PSD) functions and turbulent kinetic energy (TKE) derived from the five-hole probe are compared with sonic anemometers on a meteorological mast. During a BACCHUS field campaign at Mace Head Atmospheric Research Station (Ireland), a fleet of RPAs was deployed to profile the atmosphere and complement ground-based and satellite observations of physical and chemical properties of aerosols, clouds, and meteorological state parameters. The five-hole probe was flown on straight-and-level legs to measure vertical wind velocities within clouds. The vertical velocity measurements from the RPA are validated with vertical velocities derived from a ground-based cloud radar by showing that both measurements yield model-simulated cloud droplet number concentrations within 10 %. The updraft velocity distributions illustrate distinct relationships between vertical cloud fields in different meteorological conditions.

Reward Devaluation: Dot-Probe Meta-Analytic Evidence of Avoidance of Positive Information in Depressed Persons

PubMed Central

Winer, E. Samuel; Salem, Taban

2015-01-01

Cognitive theories of depression and anxiety have traditionally emphasized the role of attentional biases in the processing of negative information. The dot-probe task has been widely used to study this phenomenon. Recent findings suggest that biased processing of positive information might also be an important aspect of developing psychopathological symptoms. However, despite some evidence suggesting persons with symptoms of depression and anxiety may avoid positive information, many dot-probe studies have produced null findings. The present review used conventional and novel meta-analytic methods to evaluate dot-probe attentional biases away from positive information and, for comparison, toward negative information, in depressed and anxious individuals. Results indicated that avoidance of positive information is a real effect exhibiting substantial evidential value among persons experiencing psychopathology, with individuals evidencing primary symptoms of depression clearly demonstrating this effect. Different theoretical explanations for these findings are evaluated, including those positing threat-processing structures, even-handedness, self-regulation, and reward devaluation, with the novel theory of reward devaluation emphasized and expanded. These novel findings and theory suggest that avoidance of prospective reward helps to explain the cause and sustainability of depressed states. Suggestions for future research and methodological advances are discussed. PMID:26619211

Theoretical simulation of the dual-heat-flux method in deep body temperature measurements.

PubMed

Huang, Ming; Chen, Wenxi

2010-01-01

Deep body temperature reveals individual physiological states, and is important in patient monitoring and chronobiological studies. An innovative dual-heat-flux method has been shown experimentally to be competitive with the conventional zero-heat-flow method in its performance, in terms of measurement accuracy and step response to changes in the deep temperature. We have utilized a finite element method to model and simulate the dynamic process of a dual-heat-flux probe in deep body temperature measurements to validate the fundamental principles of the dual-heat-flux method theoretically, and to acquire a detailed quantitative description of the thermal profile of the dual-heat-flux probe. The simulation results show that the estimated deep body temperature is influenced by the ambient temperature (linearly, at a maximum rate of 0.03 °C/°C) and the blood perfusion rate. The corresponding depth of the estimated temperature in the skin and subcutaneous tissue layer is consistent when using the dual-heat-flux probe. Insights in improving the performance of the dual-heat-flux method were discussed for further studies of dual-heat-flux probes, taking into account structural and geometric considerations.

Low-temperature electron-spin relaxation in the crystalline and glassy states of solid ethanol

NASA Astrophysics Data System (ADS)

Kveder, Marina; Merunka, Dalibor; Jokić, Milan; Rakvin, Boris

2008-03-01

X -band electron paramagnetic resonance spectroscopy was used to study the spectral properties of a nitroxide spin probe in ethanol glass and crystalline ethanol, at 5-11.5K . The different anisotropy of molecular packing in the two host matrices was evidenced by different rigid limit values for maximal hyperfine splitting in the signal of the spin probe. The significantly shorter phase memory time Tm for the spin probe dissolved in crystalline ethanol, as compared to ethanol glass, was discussed in terms of contribution from spectral diffusion. The effect of low-frequency dynamics was manifested in the temperature dependence of Tm and in the difference between the data measured at different spectral positions. This phenomenon was addressed within the framework of the slow-motional isotropic diffusion model [S. Lee and S. Z. Tang, Phys. Rev. B 31, 1308 (1985)] predicting the spin probe dynamics within the millisecond range, at very low temperatures. The shorter spin-lattice relaxation time of the spin probe in ethanol glass was interpreted in terms of enhanced energy exchange between the spin system and the lattice in the glass matrix due to boson peak excitations.

Final report: Mapping Interactions in Hybrid Systems with Active Scanning Probes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Berezovsky, Jesse

2017-09-29

This project aimed to study and map interactions between components of hybrid nanodevices using a novel scanning probe approach. To enable this work, we initially constructed a flexible experimental apparatus allowing for simultaneous scanning probe and confocal optical microscopy measurements. This setup was first used for all-optical measurements of nanostructures, with the focus then shifting to hybrid devices in which single coherent electron spins are coupled to micron-scale ferromagnetic elements, which may prove useful for addressing single spins, enhanced sensing, or spin-wave-mediated coupling of spins for quantum information applications. A significant breakthrough was the realization that it is not necessarymore » to fabricate a magnetic structure on a scanning probe – instead a ferromagnetic vortex core can act as an integrated, solid state, scanning probe. The core of the vortex produces a very strong, localized fringe field which can be used analogously to an MFM tip. Unlike a traditional MFM tip, however, the vortex core is scanned within an integrated device (eliminating drift), and can be moved on vastly faster timescales. This approach allows the detailed investigation of interactions between single spins and complex driven ferromagnetic dynamics.« less

Probing the energy levels of perovskite solar cells via Kelvin probe and UV ambient pressure photoemission spectroscopy.

PubMed

Harwell, J R; Baikie, T K; Baikie, I D; Payne, J L; Ni, C; Irvine, J T S; Turnbull, G A; Samuel, I D W

2016-07-20

The field of organo-lead halide perovskite solar cells has been rapidly growing since their discovery in 2009. State of the art devices are now achieving efficiencies comparable to much older technologies like silicon, while utilising simple manufacturing processes and starting materials. A key parameter to consider when optimising solar cell devices or when designing new materials is the position and effects of the energy levels in the materials. We present here a comprehensive study of the energy levels present in a common structure of perovskite solar cell using an advanced macroscopic Kelvin probe and UV air photoemission setup. By constructing a detailed map of the energy levels in the system we are able to predict the importance of each layer to the open circuit voltage of the solar cell, which we then back up through measurements of the surface photovoltage of the cell under white illumination. Our results demonstrate the effectiveness of air photoemission and Kelvin probe contact potential difference measurements as a method of identifying the factors contributing to the open circuit voltage in a solar cell, as well as being an excellent way of probing the physics of new materials.

Pump-Flow-Probe X-Ray Absorption Spectroscopy as a Tool for Studying Intermediate States of Photocatalytic Systems.

PubMed

Smolentsev, Grigory; Guda, Alexander; Zhang, Xiaoyi; Haldrup, Kristoffer; Andreiadis, Eugen; Chavarot-Kerlidou, Murielle; Canton, Sophie E; Nachtegaal, Maarten; Artero, Vincent; Sundstrom, Villy

2013-08-29

A new setup for pump-flow-probe X-ray absorption spectroscopy has been implemented at the SuperXAS beamline of the Swiss Light Source. It allows recording X-ray absorption spectra with a time resolution of tens of microseconds and high detection efficiency for samples with sub-mM concentrations. A continuous wave laser is used for the photoexcitation, with the distance between laser and X-ray beams and velocity of liquid flow determining the time delay, while the focusing of both beams and the flow speed define the time resolution. This method is compared with the alternative measurement technique that utilizes a 1 kHz repetition rate laser and multiple X-ray probe pulses. Such an experiment was performed at beamline 11ID-D of the Advanced Photon Source. Advantages, limitations and potential for improvement of the pump-flow-probe setup are discussed by analyzing the photon statistics. Both methods, with Co K-edge probing were applied to the investigation of a cobaloxime-based photo-catalytic reaction. The interplay between optimizing for efficient photoexcitation and time resolution as well as the effect of sample degradation for these two setups are discussed.

Pump-Flow-Probe X-Ray Absorption Spectroscopy as a Tool for Studying Intermediate States of Photocatalytic Systems

PubMed Central

Smolentsev, Grigory; Guda, Alexander; Zhang, XIaoyi; Haldrup, Kristoffer; Andreiadis, Eugen; Chavarot-Kerlidou, Murielle; Canton, Sophie E.; Nachtegaal, Maarten; Artero, Vincent; Sundstrom, Villy

2014-01-01

A new setup for pump-flow-probe X-ray absorption spectroscopy has been implemented at the SuperXAS beamline of the Swiss Light Source. It allows recording X-ray absorption spectra with a time resolution of tens of microseconds and high detection efficiency for samples with sub-mM concentrations. A continuous wave laser is used for the photoexcitation, with the distance between laser and X-ray beams and velocity of liquid flow determining the time delay, while the focusing of both beams and the flow speed define the time resolution. This method is compared with the alternative measurement technique that utilizes a 1 kHz repetition rate laser and multiple X-ray probe pulses. Such an experiment was performed at beamline 11ID-D of the Advanced Photon Source. Advantages, limitations and potential for improvement of the pump-flow-probe setup are discussed by analyzing the photon statistics. Both methods, with Co K-edge probing were applied to the investigation of a cobaloxime-based photo-catalytic reaction. The interplay between optimizing for efficient photoexcitation and time resolution as well as the effect of sample degradation for these two setups are discussed. PMID:24443663

Probing the solvation structure and dynamics in ionic liquids by time-resolved infrared spectroscopy of 4-(dimethylamino)benzonitrile.

PubMed

Ando, Rômulo A; Brown-Xu, Samantha E; Nguyen, Lisa N Q; Gustafson, Terry L

2017-09-20

In this work we demonstrate the use of the push-pull model system 4-(dimethylamino)benzonitrile (DMABN) as a convenient molecular probe to investigate the local solvation structure and dynamics by means of time-resolved infrared spectroscopy (TRIR). The photochemical features associated with this system provide several advantages due to the high charge separation between the ground and charge transfer states involving the characteristic nitrile bond, and an excited state lifetime that is long enough to observe the slow solvation dynamics in organic solvents and ionic liquids. The conversion from a locally excited state to an intramolecular charge transfer state (LE-ICT) in ionic liquids shows similar kinetic lifetimes in comparison to organic solvents. This similarity confirms that such conversion depends solely on the intramolecular reorganization of DMABN in the excited state, and not by the dynamics of solvation. In contrast, the relative shift of the ν(CN) vibration during the relaxation of the ICT state reveals two distinct lifetimes that are sensitive to the solvent environment. This study reveals a fast time component which is attributed to the dipolar relaxation of the solvent and a slower time component related to the rotation of the dimethylamino group of DMABN.

Structural and rheological relaxation upon flow cessation in colloidal dispersions: Transient, nonlinear microrheology

NASA Astrophysics Data System (ADS)

Mohanty, Ritesh P.; Zia, Roseanna N.

2017-11-01

We theoretically study the impact of particle roughness, Brownian motion, and hydrodynamic interactions on the relaxation of colloidal dispersions by examining the structural and rheological relaxation after microrheological flow cessation. In particular, we focus on the disparity in timescales over which hydrodynamic and entropic forces act and influence colloidal relaxation. To do this, we employ the active microrheology framework, in which a colloidal probe, driven by an arbitrarily strong external force, interacts with many surrounding particle configurations before reaching steady-state motion. We utilize the steady-state structure around the probe as the initial condition in a Smoluchowski equation that we solve to obtain the structural evolution upon flow cessation. We systematically tune the strength of hydrodynamic and entropic forces, and study their influence on structural and rheological relaxation. Upon cessation, the non-Newtonian behavior arising directly from hydrodynamic forces dissipates instantaneously, while the entropic contributions decay over longer times. We find that increasing pre-cessation external flow strength enhances the relaxation rate, while hydrodynamic interactions slow down the relaxation.

Probing Ultrafast Electron Dynamics at Surfaces Using Soft X-Ray Transient Reflectivity Spectroscopy

NASA Astrophysics Data System (ADS)

Baker, L. Robert; Husek, Jakub; Biswas, Somnath; Cirri, Anthony

The ability to probe electron dynamics with surface sensitivity on the ultrafast time scale is critical for understanding processes such as charge separation, injection, and surface trapping that mediate efficiency in catalytic and energy conversion materials. Toward this goal, we have developed a high harmonic generation (HHG) light source for femtosecond soft x-ray reflectivity. Using this light source we investigated the ultrafast carrier dynamics at the surface of single crystalline α-Fe2O3, polycrystalline α-Fe2O3, and the mixed metal oxide, CuFeO2. We have recently demonstrated that CuFeO2 in particular is a selective catalyst for photo-electrochemical CO2 reduction to acetate; however, the role of electronic structure and charge carrier dynamics in mediating catalytic selectivity has not been well understood. Soft x-ray reflectivity measurements probe the M2,3, edges of the 3d transition metals, which provide oxidation and spin state resolution with element specificity. In addition to chemical state specificity, these measurements are also surface sensitive, and by independently simulating the contributions of the real and imaginary components of the complex refractive index, we can differentiate between surface and sub-surface contributions to the excited state spectrum. Accordingly, this work demonstrates the ability to probe ultrafast carrier dynamics in catalytic materials with element and chemical state specificity and with surface sensitivity.

Mode pumping experiments on biomolecules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Austin, R.H.; Erramilli, S.; Xie, A.

1995-12-31

We will explore several aspects of protein dynamics and energy transfer that can be explored by using the intense, picosecond, tunable mid-IR output of the FEL. In order of appearance they are: (1) Saturation recovery and inter-level coupling of the low temperature amide-I band in acetanilide. This is a continuation of earlier experiments to test soliton models in crystalline hydrogen bonded solids. In this experiment we utilize the sub-picosecond time resolution and low repetition rate of the Stanford SCLA FEL to do both T{sub 1} and T{sub 2} relaxation measurements at 1650 cm{sup -1}. (2) Probing the influence of collectivemore » dynamics in sensory rhodopsin. In this experiment we use the FIR output of the Stanford FIREFLY FEL to determine the lifetime of collective modes in the photo-active protein sensory rhodopsin, and begin experiments on the influence of collective modes on retinal reaction dynamics. (3) Probing the transition states of enzymes. This experiment, in the initial stages, attempts to use the intense IR output of the FEL to probe and influence the reaction path of a transition state analog for the protein nucleoside hydrolase. The transition state of the inosine substrate is believed to have critical modes softened by the protein so that bond-breaking paths show absorption at approximately 800 cm{sup -1}. A form of action spectrum using FEL excitation will be used to probe this state.« less

Exciton-controlled fluorescence: application to hybridization-sensitive fluorescent DNA probe.

PubMed

Okamoto, Akimitsu; Ikeda, Shuji; Kubota, Takeshi; Yuki, Mizue; Yanagisawa, Hiroyuki

2009-01-01

A hybridization-sensitive fluorescent probe has been designed for nucleic acid detection, using the concept of fluorescence quenching caused by the intramolecular excitonic interaction of fluorescence dyes. We synthesized a doubly thiazole orange-labeled nucleotide showing high fluorescence intensity for a hybrid with the target nucleic acid and effective quenching for the single-stranded state. This exciton-controlled fluorescent probe was applied to living HeLa cells using microinjection to visualize intracellular mRNA localization. Immediately after injection of the probe into the cell, fluorescence was observed from the probe hybridizing with the target RNA. This fluorescence rapidly decreased upon addition of a competitor DNA. Multicoloring of this probe resulted in the simple simultaneous detection of plural target nucleic acid sequences. This probe realized a large, rapid, reversible change in fluorescence intensity in sensitive response to the amount of target nucleic acid, and facilitated spatiotemporal monitoring of the behavior of intracellular RNA.

Power Balance Analysis of the Prototype-Material Plasma Exposure eXperiment

NASA Astrophysics Data System (ADS)

Showers, M. A.; Biewer, T. M.; Caneses, J. F.; Caughman, J. B. O.; Lumsdaine, A.; Owen, L.; Rapp, J.; Youchison, D.; Beers, C. J.; Donovan, D. C.; Kafle, N.; Ray, H. B.

2017-10-01

The Prototype-Material Plasma Exposure eXperiment (Proto-MPEX) is a test bed for the plasma source concept for the planned Material Plasma Exposure eXperiment (MPEX), a steady-state linear device studying plasma material interactions for fusion reactors. A power balance of Proto-MPEX attempts to identify machine operating parameters that will improve Proto-MPEX's performance, potentially impacting the MPEX design concept. A power balance has been performed utilizing an extensive diagnostic suite to identify mechanisms and locations of power loss from the main plasma. The diagnostic package includes infrared cameras, double Langmuir probes, fluoroptic probes, Mach probes, a Thomson scattering diagnostic, a McPherson spectrometer and in-vessel thermocouples. Radiation losses are estimated with absolute calibrated spectroscopic signals. This work was supported by the U.S. D.O.E. contract DE-AC05-00OR22725.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Godfrey, T. J.; Yu, Hui; Ullrich, Susanne, E-mail: ullrich@physast.uga.edu

The studies herein investigate the involvement of the low-lying {sup 1}L{sub a} and {sup 1}L{sub b} states with {sup 1}ππ{sup *} character and the {sup 1}πσ{sup *} state in the deactivation process of indole following photoexcitation at 201 nm. Three gas-phase, pump-probe spectroscopic techniques are employed: (1) Time-resolved photoelectron spectroscopy (TR-PES), (2) hydrogen atom (H-atom) time-resolved kinetic energy release (TR-KER), and (3) time-resolved ion yield (TR-IY). Each technique provides complementary information specific to the photophysical processes in the indole molecule. In conjunction, a thorough examination of the electronically excited states in the relaxation process, with particular focus on the involvement ofmore » the {sup 1}πσ{sup *} state, is afforded. Through an extensive analysis of the TR-PES data presented here, it is deduced that the initial excitation of the {sup 1}B{sub b} state decays to the {sup 1}L{sub a} state on a timescale beyond the resolution of the current experimental setup. Relaxation proceeds on the {sup 1}L{sub a} state with an ultrafast decay constant (<100 femtoseconds (fs)) to the lower-lying {sup 1}L{sub b} state, which is found to possess a relatively long lifetime of 23 ± 5 picoseconds (ps) before regressing to the ground state. These studies also manifest an additional component with a relaxation time of 405 ± 76 fs, which is correlated with activity along the {sup 1}πσ{sup *} state. TR-KER and TR-IY experiments, both specifically probing {sup 1}πσ{sup *} dynamics, exhibit similar decay constants, further validating these observations.« less

Vibronic singlet and triplet steady-state interplay emissions in phenazine-based 1,2,3-triazole films

NASA Astrophysics Data System (ADS)

Costa, Bárbara B. A.; Souza, Paula D. C.; Gontijo, Rafael N.; Jardim, Guilherme A. M.; Moreira, Roberto L.; da Silva, Eufrânio N.; Cury, Luiz A.

2018-03-01

Photoluminescence and phosphorescence emissions of solid-state phenazine films were investigated in steady-state experimental conditions. Important discrepancies were observed for blended films where a host optically inert matrix was introduced to disperse the probe molecules. A vibronic spin-orbit phosphorescent emission clearly appeared, while for the films solely composed by the probe molecules, the phosphorescence broadened and presented a structureless shape, shifted to longer wavelengths. Further Arrhenius behavior analysis on the photoluminescent and phosphorescent emissions on temperature, corroborated the direct and reverse intersystem crossing interplay between singlet and triplet states. Molecular aggregation is responsible for the deterioration of non-blended triazole films phosphorescence.

Polyethylene glycol versus dual sugar assay for gastrointestinal permeability analysis: is it time to choose?

PubMed

van Wijck, Kim; Bessems, Babs Afm; van Eijk, Hans Mh; Buurman, Wim A; Dejong, Cornelis Hc; Lenaerts, Kaatje

2012-01-01

Increased intestinal permeability is an important measure of disease activity and prognosis. Currently, many permeability tests are available and no consensus has been reached as to which test is most suitable. The aim of this study was to compare urinary probe excretion and accuracy of a polyethylene glycol (PEG) assay and dual sugar assay in a double-blinded crossover study to evaluate probe excretion and the accuracy of both tests. Gastrointestinal permeability was measured in nine volunteers using PEG 400, PEG 1500, and PEG 3350 or lactulose-rhamnose. On 4 separate days, permeability was analyzed after oral intake of placebo or indomethacin, a drug known to increase intestinal permeability. Plasma intestinal fatty acid binding protein and calprotectin levels were determined to verify compromised intestinal integrity after indomethacin consumption. Urinary samples were collected at baseline, hourly up to 5 hours after probe intake, and between 5 and 24 hours. Urinary excretion of PEG and sugars was determined using high-pressure liquid chromatography-evaporative light scattering detection and liquid chromatography-mass spectrometry, respectively. Intake of indomethacin increased plasma intestinal fatty acid-binding protein and calprotectin levels, reflecting loss of intestinal integrity and inflammation. In this state of indomethacin-induced gastrointestinal compromise, urinary excretion of the three PEG probes and lactulose increased compared with placebo. Urinary PEG 400 excretion, the PEG 3350/PEG 400 ratio, and the lactulose/rhamnose ratio could accurately detect indomethacin-induced increases in gastrointestinal permeability, especially within 2 hours of probe intake. Hourly urinary excretion and diagnostic accuracy of PEG and sugar probes show high concordance for detection of indomethacin-induced increases in gastrointestinal permeability. This comparative study improves our knowledge of permeability analysis in man by providing a clear overview of both tests and demonstrates equivalent performance in the current setting.

Ultrafast electron microscopy in materials science, biology, and chemistry

NASA Astrophysics Data System (ADS)

King, Wayne E.; Campbell, Geoffrey H.; Frank, Alan; Reed, Bryan; Schmerge, John F.; Siwick, Bradley J.; Stuart, Brent C.; Weber, Peter M.

2005-06-01

The use of pump-probe experiments to study complex transient events has been an area of significant interest in materials science, biology, and chemistry. While the emphasis has been on laser pump with laser probe and laser pump with x-ray probe experiments, there is a significant and growing interest in using electrons as probes. Early experiments used electrons for gas-phase diffraction of photostimulated chemical reactions. More recently, scientists are beginning to explore phenomena in the solid state such as phase transformations, twinning, solid-state chemical reactions, radiation damage, and shock propagation. This review focuses on the emerging area of ultrafast electron microscopy (UEM), which comprises ultrafast electron diffraction (UED) and dynamic transmission electron microscopy (DTEM). The topics that are treated include the following: (1) The physics of electrons as an ultrafast probe. This encompasses the propagation dynamics of the electrons (space-charge effect, Child's law, Boersch effect) and extends to relativistic effects. (2) The anatomy of UED and DTEM instruments. This includes discussions of the photoactivated electron gun (also known as photogun or photoelectron gun) at conventional energies (60-200 keV) and extends to MeV beams generated by rf guns. Another critical aspect of the systems is the electron detector. Charge-coupled device cameras and microchannel-plate-based cameras are compared and contrasted. The effect of various physical phenomena on detective quantum efficiency is discussed. (3) Practical aspects of operation. This includes determination of time zero, measurement of pulse-length, and strategies for pulse compression. (4) Current and potential applications in materials science, biology, and chemistry. UEM has the potential to make a significant impact in future science and technology. Understanding of reaction pathways of complex transient phenomena in materials science, biology, and chemistry will provide fundamental knowledge for discovery-class science.

Real-Time Hand-Held Magnetometer Array

DTIC Science & Technology

2016-04-01

54 7.2.4 Detection : Probe Laser...oscillations in the F=4 hyperfine ground state and the probe beam is used to detect the oscillations. ............ 50 Figure 52. Sensor Larmor signal...level detectable by the magnetometer with a signal to noise ratio of 1:1

Assessment Report of US-Japan-Europe Collaborative Research on Probe Data International Probe Data Work Group Phase 2.

DOT National Transportation Integrated Search

2016-01-01

The United States Department of Transportation (USDOT), the Road Bureau of Ministry of Land, Infrastructure, Transport, and Tourism (MLIT) of Japan, and the European Unions European Commission Directorate General for Communications Networks, Conte...

Femtosecond optical reflectivity measurements of lattice-mediated spin repulsions in photoexcited LaCoO3 thin films

NASA Astrophysics Data System (ADS)

Bielecki, J.; Rata, A. D.; Börjesson, L.

2014-01-01

We present results on the temperature dependence of ultrafast electron and lattice dynamics, measured with pump-probe transient reflectivity experiments, of an epitaxially grown LaCoO3 thin film under tensile strain. Probing spin-polarized transitions into the antibonding eg band provides a measure of the low-spin fraction, both as a function of temperature and time after photoexcitation. It is observed that femtosecond laser pulses destabilize the constant low-spin fraction (˜63%-64%) in equilibrium into a thermally activated state, driven by a subpicosecond change in spin gap Δ. From the time evolution of the low-spin fraction, it is possible to disentangle the thermal and lattice contributions to the spin state. A lattice mediated spin repulsion, identified as the governing factor determining the equilibrium spin state in thin-film LaCoO3, is observed. These results suggests that time-resolved spectroscopy is a sensitive probe of the spin state in LaCoO3 thin films, with the potential to bring forward quantitative insight into the complicated interplay between structure and spin state in LaCoO3.

Optimizing the choice of spin-squeezed states for detecting and characterizing quantum processes

DOE PAGES

Rozema, Lee A.; Mahler, Dylan H.; Blume-Kohout, Robin; ...

2014-11-07

Quantum metrology uses quantum states with no classical counterpart to measure a physical quantity with extraordinary sensitivity or precision. Most such schemes characterize a dynamical process by probing it with a specially designed quantum state. The success of such a scheme usually relies on the process belonging to a particular one-parameter family. If this assumption is violated, or if the goal is to measure more than one parameter, a different quantum state may perform better. In the most extreme case, we know nothing about the process and wish to learn everything. This requires quantum process tomography, which demands an informationallymore » complete set of probe states. It is very convenient if this set is group covariant—i.e., each element is generated by applying an element of the quantum system’s natural symmetry group to a single fixed fiducial state. In this paper, we consider metrology with 2-photon (“biphoton”) states and report experimental studies of different states’ sensitivity to small, unknown collective SU( 2) rotations [“ SU( 2) jitter”]. Maximally entangled N00 N states are the most sensitive detectors of such a rotation, yet they are also among the worst at fully characterizing an a priori unknown process. We identify (and confirm experimentally) the best SU( 2)-covariant set for process tomography; these states are all less entangled than the N00 N state, and are characterized by the fact that they form a 2-design.« less

Charge Transfer Processes in OPV Materials as Revealed by EPR Spectroscopy

DOE PAGES

Niklas, Jens; Poluektov, Oleg

2017-03-03

Understanding charge separation and charge transport at a molecular level is crucial for improving the efficiency of organic photovoltaic (OPV) cells. Under illumination of Bulk Heterojunction (BHJ) blends of polymers and fullerenes, various paramagnetic species are formed including polymer and fullerene radicals, radical pairs, and photoexcited triplet states. Light-induced Electron Paramagnetic Resonance (EPR) spectroscopy is ideally suited to study these states in BHJ due to its selectivity in probing the paramagnetic intermediates. Some advanced EPR techniques like light-induced ENDOR spectroscopy and pulsed techniques allow the determination of hyperfine coupling tensors, while high-frequency EPR allows the EPR signals of the individualmore » species to be resolved and their g-tensors to be determined. In these magnetic resonance parameters reveal details about the delocalization of the positive polaron on the various polymer donors which is important for the efficient charge separation in BHJ systems. Time-resolved EPR can contribute to the study of the dynamics of charge separation, charge transfer and recombination in BHJ by probing the unique spectral signatures of charge transfer and triplet states. Furthermore, the potential of the EPR also allows characterization of the intermediates and products of BHJ degradation.« less

High-order multipole radiation from quantum Hall states in Dirac materials

NASA Astrophysics Data System (ADS)

Gullans, Michael J.; Taylor, Jacob M.; Imamoǧlu, Ataç; Ghaemi, Pouyan; Hafezi, Mohammad

2017-06-01

We investigate the optical response of strongly disordered quantum Hall states in two-dimensional Dirac materials and find qualitatively different effects in the radiation properties of the bulk versus the edge. We show that the far-field radiation from the edge is characterized by large multipole moments (>50 ) due to the efficient transfer of angular momentum from the electrons into the scattered light. The maximum multipole transition moment is a direct measure of the coherence length of the edge states. Accessing these multipole transitions would provide new tools for optical spectroscopy and control of quantum Hall edge states. On the other hand, the far-field radiation from the bulk appears as random dipole emission with spectral properties that vary with the local disorder potential. We determine the conditions under which this bulk radiation can be used to image the disorder landscape. Such optical measurements can probe submicron-length scales over large areas and provide complementary information to scanning probe techniques. Spatially resolving this bulk radiation would serve as a novel probe of the percolation transition near half filling.

Dynamics of molecules in extreme rotational states

PubMed Central

Yuan, Liwei; Teitelbaum, Samuel W.; Robinson, Allison; Mullin, Amy S.

2011-01-01

We have constructed an optical centrifuge with a pulse energy that is more than 2 orders of magnitude larger than previously reported instruments. This high pulse energy enables us to create large enough number densities of molecules in extreme rotational states to perform high-resolution state-resolved transient IR absorption measurements. Here we report the first studies of energy transfer dynamics involving molecules in extreme rotational states. In these studies, the optical centrifuge drives CO2 molecules into states with J ∼ 220 and we use transient IR probing to monitor the subsequent rotational, translational, and vibrational energy flow dynamics. The results reported here provide the first molecular insights into the relaxation of molecules with rotational energy that is comparable to that of a chemical bond.

A hot-spot-active magnetic graphene oxide substrate for microRNA detection based on cascaded chemiluminescence resonance energy transfer

NASA Astrophysics Data System (ADS)

Bi, Sai; Chen, Min; Jia, Xiaoqiang; Dong, Ying

2015-02-01

Herein, a cascaded chemiluminescence resonance energy transfer (C-CRET) process was demonstrated from horseradish peroxidase (HRP)-mimicking DNAzyme-catalyzed luminol-H2O2 to fluorescein and further to graphene oxide (GO) when HRP-mimicking DNAzyme/fluorescein was in close proximity to the GO surface. The proposed C-CRET system was successfully implemented to construct three modes of C-CRET hot-spot-active substrates (modes I, II and III) by covalently immobilizing HRP-mimicking DNAzyme/fluorescein-labeled hairpin DNAs (hot-spot-generation probes) on magnetic GO (MGO), resulting in a signal ``off'' state due to the quenching of the luminol/H2O2/HRP-mimicking DNAzyme/fluorescein CRET system by GO. Upon the introduction of microRNA-122 (miRNA-122), the targets (mode I) or the new triggers that were generated through a strand displacement reaction (SDR) initiated by miRNA-122 (modes II and III) hybridized with the loop domains of hairpin probes on MGO to form double-stranded (modes I and II) or triplex-stem structures (mode III), causing an ``open'' configuration of the hairpin probe and a CRET signal ``on'' state, thus achieving sensitive and selective detection of miRNA-122. More importantly, the substrate exhibited excellent controllability, reversibility and reproducibility through SDR and magnetic separation (modes II and III), especially sequence-independence for hairpin probes in mode III, holding great potential for the development of a versatile platform for optical biosensing.Herein, a cascaded chemiluminescence resonance energy transfer (C-CRET) process was demonstrated from horseradish peroxidase (HRP)-mimicking DNAzyme-catalyzed luminol-H2O2 to fluorescein and further to graphene oxide (GO) when HRP-mimicking DNAzyme/fluorescein was in close proximity to the GO surface. The proposed C-CRET system was successfully implemented to construct three modes of C-CRET hot-spot-active substrates (modes I, II and III) by covalently immobilizing HRP-mimicking DNAzyme/fluorescein-labeled hairpin DNAs (hot-spot-generation probes) on magnetic GO (MGO), resulting in a signal ``off'' state due to the quenching of the luminol/H2O2/HRP-mimicking DNAzyme/fluorescein CRET system by GO. Upon the introduction of microRNA-122 (miRNA-122), the targets (mode I) or the new triggers that were generated through a strand displacement reaction (SDR) initiated by miRNA-122 (modes II and III) hybridized with the loop domains of hairpin probes on MGO to form double-stranded (modes I and II) or triplex-stem structures (mode III), causing an ``open'' configuration of the hairpin probe and a CRET signal ``on'' state, thus achieving sensitive and selective detection of miRNA-122. More importantly, the substrate exhibited excellent controllability, reversibility and reproducibility through SDR and magnetic separation (modes II and III), especially sequence-independence for hairpin probes in mode III, holding great potential for the development of a versatile platform for optical biosensing. Electronic supplementary information (ESI) available: Sequences of RNA and DNA used in this study, relationship of the proposed three modes, CRET mechanism of the luminol/H2O2/HRP-mimicking DNAzyme/fluorescein system, calculation of the surface coverage of hairpin probe I-1 on MGO, control experiment, comparison between different modes for microRNA detection, and advantages of the proposed strategy. See DOI: 10.1039/c4nr06603k

Time-resolved coherent Raman spectroscopy by high-speed pump-probe delay scanning.

PubMed

Domingue, S R; Winters, D G; Bartels, R A

2014-07-15

Using a spinning window pump-probe delay scanner, we demonstrate a means of acquiring time-resolved vibrational spectra at rates up to 700 Hz. The time-dependent phase shift accumulated by the probe pulse in the presence of a coherently vibrating sample gives rise to a Raman-induced frequency shifting readily detectable in a balanced detector. This rapid delay scanning system represents a 23-fold increase in averaging speed and is >10× faster than state-of-the-art voice coil delay lines. These advancements make pump-probe spectroscopy a more practical means of imaging complex media.

Ultrafast Optical Microscopy of Single Monolayer Molybdenum Disulfide Flakes

DOE PAGES

Seo, Minah; Yamaguchi, Hisato; Mohite, Aditya D.; ...

2016-02-15

We performed ultrafast optical microscopy on single flakes of atomically thin CVD-grown molybdenum disulfide, using non-degenerate femtosecond pump-probe spectroscopy to excite and probe carriers above and below the indirect and direct band gaps. These measurements reveal the influence of layer thickness on carrier dynamics when probing near the band gap. Furthermore, fluence-dependent measurements indicate that carrier relaxation is primarily influenced by surface-related defect and trap states after above-bandgap photoexcitation. Furthermore, the ability to probe femtosecond carrier dynamics in individual flakes can thus give much insight into light-matter interactions in these two-dimensional nanosystems.

Exploring 12'-apo-beta-carotenoic-12'-acid as an ultrafast polarity probe for ionic liquids.

PubMed

Lohse, Peter W; Bürsing, Reinhard; Lenzer, Thomas; Oum, Kawon

2008-03-13

The ultrafast excited-state dynamics of the carbonyl-containing carotenoid 12'-apo-beta-carotenoic-12'-acid (12'CA) have been used for probing the microscopic environment in various ionic liquids (ILs). The following IL cations were investigated: 1,3-di-n-alkyl-imidazolium featuring different n-alkyl chain lengths and also additional methylation at the C2 position, triethylsulfonium, as well as two tetraalkylammonium ions. These were combined with different anions: [BF4]-, [PF6]-, ethyl sulfate ([EtOSO3]-), and bis(trifluoromethylsulfonyl)amide ([Tf2N]-). The probe molecule was excited via the S0 --> S2 transition at 425 or 430 nm, and the characteristic stimulated emission decay of the low-lying excited electronic S1/ICT (intramolecular charge transfer) state of 12'CA was monitored in the near IR (850 or 860 nm). Its lifetime tau1 is sensitive to the micropolarity-induced stabilization of S1/ICT relative to S0. The lifetime tau1 of the S1/ICT state varies only moderately in all ionic liquids studied here ( approximately 40-110 ps), which lies in the range between ethanol (109 ps) and methanol (49 ps). While organic solvents show an excellent correlation of tau1 with the solvent polarity function Deltaf = (epsilon - 1)/(epsilon + 2) - (n2 - 1)/(n2 + 2), where epsilon and n are the static dielectric constant and the refractive index of the solvent, respectively, this is not the case for ILs. This is due to dominant local electrostatic probe-cation interactions which cannot be easily quantified by macroscopic quantities. Methylation at the C2 position of 1,3-di-n-alkyl-imidazolium reduces the accessibility of the cation and therefore the electrostatic stabilization of the probe, resulting in an increase of tau1. A similar increase is observed upon extension of one of the n-alkyl chains from ethyl to n-decyl. Tetraalkylammonium ILs show an increased tau1 probably due to their more delocalized positive charge which cannot interact so favorably with the probe, in contrast to trialkylsulfonium ILs where the charge is more localized on the sulfur atom. The dependence of tau1 on the IL anion is much weaker, the only notable exception being [EtOSO3]-, where 12'CA experiences a less polar local environment than expected on the basis of extrapolated static dielectric constants. This is possibly due to the competition of the anion and probe for the cation interaction sites. Considerable electrostatic probe-cation interactions can be also introduced by addition of large amounts of LiClO4 salt to ethanol and diethyl ether. In this case, tau1 also strongly decreases, indicating an efficient coordination of Li+ cation(s) with the carbonyl oxygen at the negative end of the probe molecule. The S1/ICT --> S0 internal conversion of the 12'CA probe in ILs accelerates with increasing temperature, which can be characterized by an apparent activation energy of a few kJ mol-1, which is expected for energy-dependent nonradiative processes.

A Modified Alderman-Grant Coil makes possible an efficient cross-coil probe for high field solid-state NMR of lossy biological samples

NASA Astrophysics Data System (ADS)

Grant, Christopher V.; Yang, Yuan; Glibowicka, Mira; Wu, Chin H.; Park, Sang Ho; Deber, Charles M.; Opella, Stanley J.

2009-11-01

The design, construction, and performance of a cross-coil double-resonance probe for solid-state NMR experiments on lossy biological samples at high magnetic fields are described. The outer coil is a Modified Alderman-Grant Coil (MAGC) tuned to the 1H frequency. The inner coil consists of a multi-turn solenoid coil that produces a B 1 field orthogonal to that of the outer coil. This results in a compact nested cross-coil pair with the inner solenoid coil tuned to the low frequency detection channel. This design has several advantages over multiple-tuned solenoid coil probes, since RF heating from the 1H channel is substantially reduced, it can be tuned for samples with a wide range of dielectric constants, and the simplified circuit design and high inductance inner coil provides excellent sensitivity. The utility of this probe is demonstrated on two electrically lossy samples of membrane proteins in phospholipid bilayers (bicelles) that are particularly difficult for conventional NMR probes. The 72-residue polypeptide embedding the transmembrane helices 3 and 4 of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) (residues 194-241) requires a high salt concentration in order to be successfully reconstituted in phospholipid bicelles. A second application is to paramagnetic relaxation enhancement applied to the membrane-bound form of Pf1 coat protein in phospholipid bicelles where the resistance to sample heating enables high duty cycle solid-state NMR experiments to be performed.

Compact endocavity diagnostic probes for nuclear radiation detection

DOEpatents

Cui, Yonggang; James, Ralph; Bolotnikov, Aleksey

2014-08-26

This invention relates to the field of radiation imaging. In particular, the invention relates to an apparatus and a method for imaging tissue or an inanimate object using a novel probe that has an integrated solid-state semiconductor detector and complete readout electronics circuitry.

Performance measures to characterize directional corridor travel time delay based on probe vehicle data : final report.

DOT National Transportation Integrated Search

2015-10-01

Anonymous probe vehicle data are currently being collected on roadways throughout the United States. These data are being incorporated into local and statewide mobility reports to measure the performance of freeways and arterial systems. Predefined s...

Improving Middle School Parental Engagement in Transition to Common Core State Standards: An Action Research Study

ERIC Educational Resources Information Center

Harla, Donna K.

2014-01-01

Parental involvement in schools is an important potential contributor to improving American education and making the U.S. more globally competitive. This qualitative and quantitative mixed-methodology action research study probed the viability of engaging parents around issues of educational improvement by inviting them to participate in training…

Bilingual Education in English-Only: A Qualitative Case Study of Language Policy in Practice at Lincoln Elementary School

ERIC Educational Resources Information Center

Colón, Ingrid; Heineke, Amy J.

2015-01-01

In this qualitative case study, we investigate teachers' appropriation of language policy at one urban elementary school in Illinois. Recognizing classroom teachers' central role in the education of English learners, we probe teachers' policy appropriation, or how bilingual educators take state-, district-, and school-level policies and…

Quantifying Nucleic Acid Ensembles with X-ray Scattering Interferometry.

PubMed

Shi, Xuesong; Bonilla, Steve; Herschlag, Daniel; Harbury, Pehr

2015-01-01

The conformational ensemble of a macromolecule is the complete description of the macromolecule's solution structures and can reveal important aspects of macromolecular folding, recognition, and function. However, most experimental approaches determine an average or predominant structure, or follow transitions between states that each can only be described by an average structure. Ensembles have been extremely difficult to experimentally characterize. We present the unique advantages and capabilities of a new biophysical technique, X-ray scattering interferometry (XSI), for probing and quantifying structural ensembles. XSI measures the interference of scattered waves from two heavy metal probes attached site specifically to a macromolecule. A Fourier transform of the interference pattern gives the fractional abundance of different probe separations directly representing the multiple conformation states populated by the macromolecule. These probe-probe distance distributions can then be used to define the structural ensemble of the macromolecule. XSI provides accurate, calibrated distance in a model-independent fashion with angstrom scale sensitivity in distances. XSI data can be compared in a straightforward manner to atomic coordinates determined experimentally or predicted by molecular dynamics simulations. We describe the conceptual framework for XSI and provide a detailed protocol for carrying out an XSI experiment. © 2015 Elsevier Inc. All rights reserved.

The polarization anisotropy of vibrational quantum beats in resonant pump-probe experiments: Diagrammatic calculations for square symmetric molecules.

PubMed

Farrow, Darcie A; Smith, Eric R; Qian, Wei; Jonas, David M

2008-11-07

By analogy to the Raman depolarization ratio, vibrational quantum beats in pump-probe experiments depend on the relative pump and probe laser beam polarizations in a way that reflects vibrational symmetry. The polarization signatures differ from those in spontaneous Raman scattering because the order of field-matter interactions is different. Since pump-probe experiments are sensitive to vibrations on excited electronic states, the polarization anisotropy of vibrational quantum beats can also reflect electronic relaxation processes. Diagrammatic treatments, which expand use of the symmetry of the two-photon tensor to treat signal pathways with vibrational and vibronic coherences, are applied to find the polarization anisotropy of vibrational and vibronic quantum beats in pump-probe experiments for different stages of electronic relaxation in square symmetric molecules. Asymmetric vibrational quantum beats can be distinguished from asymmetric vibronic quantum beats by a pi phase jump near the center of the electronic spectrum and their disappearance in the impulsive limit. Beyond identification of vibrational symmetry, the vibrational quantum beat anisotropy can be used to determine if components of a doubly degenerate electronic state are unrelaxed, dephased, population exchanged, or completely equilibrated.

Probing nuclear effects using single-transverse kinematic imbalance with MINERvA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, X. -G.; Betancourt, M.

2016-08-15

Kinematic imbalance of the final-state particles in the plane transverse to the neutrino direction provides a sensitive probe of nuclear effects. In this contribution, we report the MINERvA measurement of the single-transverse kinematic imbalance in neutrino charged-current quasielastic-like events on CH targets. To improve the momentum measurements of the final-state particles, we develop a method to select elastically scattering contained (ESC) protons and a general procedure to correct the transverse momentum scales.

Quantum metrology and estimation of Unruh effect

PubMed Central

Wang, Jieci; Tian, Zehua; Jing, Jiliang; Fan, Heng

2014-01-01

We study the quantum metrology for a pair of entangled Unruh-Dewitt detectors when one of them is accelerated and coupled to a massless scalar field. Comparing with previous schemes, our model requires only local interaction and avoids the use of cavities in the probe state preparation process. We show that the probe state preparation and the interaction between the accelerated detector and the external field have significant effects on the value of quantum Fisher information, correspondingly pose variable ultimate limit of precision in the estimation of Unruh effect. We find that the precision of the estimation can be improved by a larger effective coupling strength and a longer interaction time. Alternatively, the energy gap of the detector has a range that can provide us a better precision. Thus we may adjust those parameters and attain a higher precision in the estimation. We also find that an extremely high acceleration is not required in the quantum metrology process. PMID:25424772

Constrained independent component analysis approach to nonobtrusive pulse rate measurements

NASA Astrophysics Data System (ADS)

Tsouri, Gill R.; Kyal, Survi; Dianat, Sohail; Mestha, Lalit K.

2012-07-01

Nonobtrusive pulse rate measurement using a webcam is considered. We demonstrate how state-of-the-art algorithms based on independent component analysis suffer from a sorting problem which hinders their performance, and propose a novel algorithm based on constrained independent component analysis to improve performance. We present how the proposed algorithm extracts a photoplethysmography signal and resolves the sorting problem. In addition, we perform a comparative study between the proposed algorithm and state-of-the-art algorithms over 45 video streams using a finger probe oxymeter for reference measurements. The proposed algorithm provides improved accuracy: the root mean square error is decreased from 20.6 and 9.5 beats per minute (bpm) for existing algorithms to 3.5 bpm for the proposed algorithm. An error of 3.5 bpm is within the inaccuracy expected from the reference measurements. This implies that the proposed algorithm provided performance of equal accuracy to the finger probe oximeter.

New Class of Quasinormal Modes of Neutron Stars in Scalar-Tensor Gravity

NASA Astrophysics Data System (ADS)

Mendes, Raissa F. P.; Ortiz, Néstor

2018-05-01

Detection of the characteristic spectrum of pulsating neutron stars can be a powerful tool not only to probe the nuclear equation of state but also to test modifications to general relativity. However, the shift in the oscillation spectrum induced by modified theories of gravity is often small and degenerate with our ignorance of the equation of state. In this Letter, we show that the coupling to additional degrees of freedom present in modified theories of gravity can give rise to new families of modes, with no counterpart in general relativity, which could be sufficiently well resolved in frequency space to allow for clear detection. We present a realization of this idea by performing a thorough study of radial oscillations of neutron stars in massless scalar-tensor theories of gravity. We anticipate astrophysical scenarios where the presence of this class of quasinormal modes could be probed with electromagnetic and gravitational wave measurements.

Frontiers in Chemical Physics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bowlan, Pamela Renee

2016-05-02

These are slides dealing with frontiers in chemical physics. The following topics are covered: Time resolving chemistry with ultrashort pulses in the 0.1-40 THz spectral range; Example: Mid-infrared absorption spectrum of the intermediate state CH 2OO; Tracking reaction dynamics through changes in the spectra; Single-shot measurement of the mid-IR absorption dynamics; Applying 2D coherent mid-IR spectroscopy to learn more about transition states; Time resolving chemical reactions at a catalysis using mid-IR and THz pulses; Studying topological insulators requires a surface sensitive probe; Nonlinear phonon dynamics in Bi 2Se 3; THz-pump, SHG-probe as a surface sensitive coherent 2D spectroscopy; Nanometer andmore » femtosecond spatiotemporal resolution mid-IR spectroscopy; Coherent two-dimensional THz/mid-IR spectroscopy with 10nm spatial resolution; Pervoskite oxides as catalysts; Functionalized graphene for catalysis; Single-shot spatiotemporal measurements; Spatiotemporal pulse measurement; Intense, broad-band THz/mid-IR generation with organic crystals.« less

Constrained independent component analysis approach to nonobtrusive pulse rate measurements.

PubMed

Tsouri, Gill R; Kyal, Survi; Dianat, Sohail; Mestha, Lalit K

2012-07-01

Nonobtrusive pulse rate measurement using a webcam is considered. We demonstrate how state-of-the-art algorithms based on independent component analysis suffer from a sorting problem which hinders their performance, and propose a novel algorithm based on constrained independent component analysis to improve performance. We present how the proposed algorithm extracts a photoplethysmography signal and resolves the sorting problem. In addition, we perform a comparative study between the proposed algorithm and state-of-the-art algorithms over 45 video streams using a finger probe oxymeter for reference measurements. The proposed algorithm provides improved accuracy: the root mean square error is decreased from 20.6 and 9.5 beats per minute (bpm) for existing algorithms to 3.5 bpm for the proposed algorithm. An error of 3.5 bpm is within the inaccuracy expected from the reference measurements. This implies that the proposed algorithm provided performance of equal accuracy to the finger probe oximeter.

Frequency-domain phase fluorometry in the presence of dark states: A numerical study

NASA Astrophysics Data System (ADS)

Zhu, Xinxin; Min, Wei

2011-11-01

Fluorescence anomalous phase advance (FAPA) is a newly discovered spectroscopy phenomenon: instead of lagging behind the modulated light, fluorescence signal can exhibit FAPA as if it precedes the excitation source in time. While FAPA offers a promising technique for probing dark state lifetime, the underlying mechanism is not fully elucidated. Herein we investigate frequency-domain phase fluorometry as a result of intricate interplay between a short-lived fluorescent state and a long-lived dark state. In particular, the quantitative dependence on modulation frequency, excitation intensity, nonradiative decay, intersystem crossing and dark-state lifetime are explored respectively. A comprehensive view of phase fluorometry emerges consequently.

A combination of alleles 2 of interleukin (IL)-1A(-889) and IL-1B(+3954) is associated with lower gingival bleeding tendency in plaque-induced gingivitis in young adults of Arabic heritage.

PubMed

Müller, H P; Barrieshi-Nusair, K M

2007-09-01

The aim of this study was to investigate the possible association of a distinct combination of polymorphisms in the interleukin (IL)-1 gene cluster on gingival bleeding tendency in young adult Arabs with plaque-induced gingivitis. Fifty otherwise healthy, nonsmoking volunteers, 19-28 years of age, participated. Clinical examinations included periodontal probing depth, bleeding on probing, and plaque index. Probing was done with a pressure-controlled probe at about 1.27 MPa. Examinations were repeated after 2 and 4 weeks. Polymorphisms in the IL-1 gene cluster were assessed using a reverse hybridization assay. A subject carrying alleles 2 at IL-1A ( -889 ) and IL-1B ( +3954 ) was designated genotype-positive. Twenty-six subjects were genotype-positive (52%). A repeated measures two-level (occasion, subject) model of the proportion of sites bleeding on probing, which was adjusted for gender, average plaque index, probing depth, and calculus, revealed a significantly lower proportion of bleeding sites in genotype-positive subjects (estimate -0.050, standard error 0.025, p < 0.05). Biserial correlations of bleeding proportions were high (0.71-0.78), confirming the steady-state plaque environment. It was concluded that inflammatory responses to dental plaque were considerably dampened in genotype-positive, nonsmoking young adults of Arabic heritage.

The effect of probe choice and solution conditions on the apparent photoreactivity of dissolved organic matter.

PubMed

Maizel, Andrew C; Remucal, Christina K

2017-08-16

Excited triplet states of dissolved organic matter ( 3 DOM) are quantified directly with the species-specific probes trans,trans-hexadienoic acid (HDA) and 2,4,6-trimethylphenol (TMP), and indirectly with the singlet oxygen ( 1 O 2 ) probe furfuryl alcohol (FFA). Although previous work suggests that these probe compounds may be sensitive to solution conditions, including dissolved organic carbon concentration ([DOC]) and pH, and may quantify different 3 DOM subpopulations, the probes have not been systematically compared. Therefore, we quantify the apparent photoreactivity of diverse environmental waters using HDA, TMP, and FFA. By conducting experiments under ambient [DOC] and pH, with standardized [DOC] and pH, and with solid phase extraction isolates, we demonstrate that much of the apparent dissimilarity in photochemical measurements is attributable to solution conditions, rather than intrinsic differences in 3 DOM production. In general, apparent quantum yields (Φ 1 O 2 ≥ Φ 3 DOM,TMP ≫ Φ 3 DOM,HDA ) and pseudo-steady state concentrations ([ 1 O 2 ] ss > [ 3 DOM] ss,TMP > [ 3 DOM] ss,HDA ) show consistent relationships in all waters under standardized conditions. However, intrinsic differences in 3 DOM photoreactivity are apparent between DOM from diverse sources, as seen in the higher Φ 1 O 2 and lower Φ 3 DOM,TMP of wastewater effluents compared with oligotrophic lakes. Additionally, while conflicting trends in photoreactivity are observed under ambient conditions, all probes observe quantum yields increasing from surface wetlands to terrestrially influenced waters to oligotrophic lakes under standardized conditions. This work elucidates how probe selection and solution conditions influence the apparent photoreactivity of environmental waters and confirms that 3 DOM or 1 O 2 probes cannot be used interchangeably in waters that vary in [DOC], pH, or DOM source.

Effects of Angular Variation on Split D Differential Eddy Current Probe Response (Postprint)

DTIC Science & Technology

2016-02-10

AFRL-RX-WP-JA-2016-0327 EFFECTS OF ANGULAR VARIATION ON SPLIT D DIFFERENTIAL EDDY CURRENT PROBE RESPONSE (POSTPRINT) Ryan D...March 2014 – 22 September 2015 4. TITLE AND SUBTITLE EFFECTS OF ANGULAR VARIATION ON SPLIT D DIFFERENTIAL EDDY CURRENT PROBE RESPONSE (POSTPRINT...last few years have seen increased levels of complexity added to push the state-of-the-art modeling software used in eddy current NDE today. The added

Ultrasensitive two-color fluorescence probes for dipole potential in phospholipid membranes

PubMed Central

Klymchenko, Andrey S.; Duportail, Guy; Mély, Yves; Demchenko, Alexander P.

2003-01-01

The principle of electrochromic modulation of excited-state intramolecular proton-transfer reaction was applied for the design of fluorescence probes with high two-color sensitivity to dipole potential, Ψd, in phospholipid bilayers. We report on the effect of Ψd variation on excitation and fluorescence spectra of two new 3-hydroxyflavone probes, which possess opposite orientations of the fluorescent moiety in the lipid bilayer. The dipole potential in the bilayer was modulated by the addition of 6-ketocholestanol or phloretin and by substitution of dimyristoyl phosphatidylcholine lipid with its ether analog 1,2-di-o-tetradecyl-sn-glycero-3-phosphocholine, and its value was estimated by the reference styryl dye 1-(3-sulfonatopropyl)-4-{β[2-(di-n-octylamino)-6-naphthyl]vinyl}pyridinium betaine. We demonstrate that after Ψd changes, the probe orienting in the bilayer similarly to the reference dye shows similar shifts in the excitation spectra, whereas the probe with the opposite orientation shows the opposite shifts. The new observation is that the response of 3-hydroxyflavone probes to Ψd in excitation spectra is accompanied by and quantitatively correlated with dramatic changes of relative intensities of the two well separated emission bands that belong to the initial normal and the product tautomer forms of the excited-state intramolecular proton-transfer reaction. This provides a strong response to Ψd by change in emission color. PMID:12972636

Evidence for out-of-equilibrium states in warm dense matter probed by x-ray Thomson scattering.

PubMed

Clérouin, Jean; Robert, Grégory; Arnault, Philippe; Ticknor, Christopher; Kress, Joel D; Collins, Lee A

2015-01-01

A recent and unexpected discrepancy between ab initio simulations and the interpretation of a laser shock experiment on aluminum, probed by x-ray Thomson scattering (XRTS), is addressed. The ion-ion structure factor deduced from the XRTS elastic peak (ion feature) is only compatible with a strongly coupled out-of-equilibrium state. Orbital free molecular dynamics simulations with ions colder than the electrons are employed to interpret the experiment. The relevance of decoupled temperatures for ions and electrons is discussed. The possibility that it mimics a transient, or metastable, out-of-equilibrium state after melting is also suggested.

Colossal super saturation of oxygen at the iron-aluminum interfaces fabricated using solid state welding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sridharan, Niyanth; Isheim, D.; Seidman, David N.

Solid state joining is achieved in three steps, (i) interface asperity deformation, (ii) oxide dispersion, followed by (iii) atomic contact and bonding. Atomically clean metallic surfaces without an oxide layer bond spontaneously. Despite its importance the oxide dispersion mechanism is not well studied. In this work the first ever atom probe study of iron-aluminum solid state welds show that the oxygen concentration at the interface is 20 at.%. This is significantly lower than any equilibrium oxide concentration. Here, we therefore propose that the high-strain rate deformation at the interfaces renders the oxide unstable resulting in the observed concentration of oxygen.

Colossal super saturation of oxygen at the iron-aluminum interfaces fabricated using solid state welding

DOE PAGES

Sridharan, Niyanth; Isheim, D.; Seidman, David N.; ...

2016-12-14

Solid state joining is achieved in three steps, (i) interface asperity deformation, (ii) oxide dispersion, followed by (iii) atomic contact and bonding. Atomically clean metallic surfaces without an oxide layer bond spontaneously. Despite its importance the oxide dispersion mechanism is not well studied. In this work the first ever atom probe study of iron-aluminum solid state welds show that the oxygen concentration at the interface is 20 at.%. This is significantly lower than any equilibrium oxide concentration. Here, we therefore propose that the high-strain rate deformation at the interfaces renders the oxide unstable resulting in the observed concentration of oxygen.

Investigation of the S1/ICT equilibrium in fucoxanthin by ultrafast pump-dump-probe and femtosecond stimulated Raman scattering spectroscopy.

PubMed

Redeckas, Kipras; Voiciuk, Vladislava; Vengris, Mikas

2016-05-01

Time-resolved multi-pulse spectroscopic methods-pump-dump-probe (PDP) and femtosecond stimulated Raman spectroscopy-were used to investigate the excited state photodynamics of the carbonyl group containing carotenoid fucoxanthin (FX). PDP experiments show that S1 and ICT states in FX are strongly coupled and that the interstate equilibrium is rapidly (<5 ps) reestablished after one of the interacting states is deliberately depopulated. Femtosecond stimulated Raman scattering experiments indicate that S1 and ICT are vibrationally distinct species. Identification of the FSRS modes on the S1 and ICT potential energy surfaces allows us to predict a possible coupling channel for the state interaction.

Unraveling the Primary Isomerization Dynamics in Cyanobacterial Phytochrome Cph1 with Multi-pulse Manipulations.

PubMed

Kim, Peter W; Rockwell, Nathan C; Freer, Lucy H; Chang, Che-Wei; Martin, Shelley S; Lagarias, J Clark; Larsen, Delmar S

2013-07-20

The ultrafast mechanisms underlying the initial photoisomerization (P r → Lumi-R) in the forward reaction of the cyanobacterial photoreceptor Cph1 were explored with multipulse pump-dump-probe transient spectroscopy. A recently postulated multi-population model was used to fit the transient pump-dump-probe and dump-induced depletion signals. We observed dump-induced depletion of the Lumi-R photoproduct, demonstrating that photoisomerization occurs via evolution on both the excited- and ground-state electronic surfaces. Excited-state equilibrium was not observed, as shown via the absence of a dump-induced excited-state "Le Châtelier redistribution" of excited-state populations. The importance of incorporating the inhomogeneous dynamics of Cph1 in interpreting measured transient data is discussed.

Unraveling the Primary Isomerization Dynamics in Cyanobacterial Phytochrome Cph1 with Multi-pulse Manipulations

PubMed Central

Kim, Peter W.; Rockwell, Nathan C.; Freer, Lucy H.; Chang, Che-Wei; Martin, Shelley S.; Lagarias, J. Clark; Larsen, Delmar S.

2013-01-01

The ultrafast mechanisms underlying the initial photoisomerization (Pr → Lumi-R) in the forward reaction of the cyanobacterial photoreceptor Cph1 were explored with multipulse pump-dump-probe transient spectroscopy. A recently postulated multi-population model was used to fit the transient pump-dump-probe and dump-induced depletion signals. We observed dump-induced depletion of the Lumi-R photoproduct, demonstrating that photoisomerization occurs via evolution on both the excited- and ground-state electronic surfaces. Excited-state equilibrium was not observed, as shown via the absence of a dump-induced excited-state “Le Châtelier redistribution” of excited-state populations. The importance of incorporating the inhomogeneous dynamics of Cph1 in interpreting measured transient data is discussed. PMID:24143267

Inverting pump-probe spectroscopy for state tomography of excitonic systems.

PubMed

Hoyer, Stephan; Whaley, K Birgitta

2013-04-28

We propose a two-step protocol for inverting ultrafast spectroscopy experiments on a molecular aggregate to extract the time-evolution of the excited state density matrix. The first step is a deconvolution of the experimental signal to determine a pump-dependent response function. The second step inverts this response function to obtain the quantum state of the system, given a model for how the system evolves following the probe interaction. We demonstrate this inversion analytically and numerically for a dimer model system, and evaluate the feasibility of scaling it to larger molecular aggregates such as photosynthetic protein-pigment complexes. Our scheme provides a direct alternative to the approach of determining all Hamiltonian parameters and then simulating excited state dynamics.

Online time-differential perturbed angular correlation study with an 19O beam - Residence sites of oxygen atoms in highly oriented pyrolytic graphite

NASA Astrophysics Data System (ADS)

Sato, W.; Ueno, H.; Watanabe, H.; Miyoshi, H.; Yoshimi, A.; Kameda, D.; Ito, T.; Shimada, K.; Kaihara, J.; Suda, S.; Kobayashi, Y.; Shinohara, A.; Ohkubo, Y.; Asahi, K.

2008-01-01

The online time-differential perturbed angular correlation (TDPAC) method was applied to a study of the physical states of a probe 19F, the β- decay product of 19O (t1/2 = 26.9 s), implanted in highly oriented pyrolytic graphite. The observed magnitude of the electric field gradient at the probe nucleus, ∣Vzz∣ = 2.91(17) × 1022 V m-2, suggests that the incident 19O atoms are stabilized at an interlayer position with point group C3v. Exhibiting observed TDPAC spectra having a clear sample-to-detector configuration dependence, we demonstrate the applicability of the present online method with a short-lived radioactive 19O beam.

Observation and quantification of the quantum dynamics of a strong-field excited multi-level system.

PubMed

Liu, Zuoye; Wang, Quanjun; Ding, Jingjie; Cavaletto, Stefano M; Pfeifer, Thomas; Hu, Bitao

2017-01-04

The quantum dynamics of a V-type three-level system, whose two resonances are first excited by a weak probe pulse and subsequently modified by another strong one, is studied. The quantum dynamics of the multi-level system is closely related to the absorption spectrum of the transmitted probe pulse and its modification manifests itself as a modulation of the absorption line shape. Applying the dipole-control model, the modulation induced by the second strong pulse to the system's dynamics is quantified by eight intensity-dependent parameters, describing the self and inter-state contributions. The present study opens the route to control the quantum dynamics of multi-level systems and to quantify the quantum-control process.

A strip-shield improves the efficiency of a solenoid coil in probes for high-field solid-state NMR of lossy biological samples.

PubMed

Wu, Chin H; Grant, Christopher V; Cook, Gabriel A; Park, Sang Ho; Opella, Stanley J

2009-09-01

A strip-shield inserted between a high inductance double-tuned solenoid coil and the glass tube containing the sample improves the efficiency of probes used for high-field solid-state NMR experiments on lossy aqueous samples of proteins and other biopolymers. A strip-shield is a coil liner consisting of thin copper strips layered on a PTFE (polytetrafluoroethylene) insulator. With lossy samples, the shift in tuning frequency is smaller, the reduction in Q, and RF-induced heating are all significantly reduced when the strip-shield is present. The performance of 800MHz (1)H/(15)N and (1)H/(13)C double-resonance probes is demonstrated on aqueous samples of membrane proteins in phospholipid bilayers.

Sum frequency generation and solid-state NMR study of the structure, orientation, and dynamics of polystyrene-adsorbed peptides

PubMed Central

Weidner, Tobias; Breen, Nicholas F.; Li, Kun; Drobny, Gary P.; Castner, David G.

2010-01-01

The power of combining sum frequency generation (SFG) vibrational spectroscopy and solid-state nuclear magnetic resonance (ssNMR) spectroscopy to quantify, with site specificity and atomic resolution, the orientation and dynamics of side chains in synthetic model peptides adsorbed onto polystyrene (PS) surfaces is demonstrated in this study. Although isotopic labeling has long been used in ssNMR studies to site-specifically probe the structure and dynamics of biomolecules, the potential of SFG to probe side chain orientation in isotopically labeled surface-adsorbed peptides and proteins remains largely unexplored. The 14 amino acid leucine-lysine peptide studied in this work is known to form an α-helical secondary structure at liquid-solid interfaces. Selective, individual deuteration of the isopropyl group in each leucine residue was used to probe the orientation and dynamics of each individual leucine side chain of LKα14 adsorbed onto PS. The selective isotopic labeling methods allowed SFG analysis to determine the orientations of individual side chains in adsorbed peptides. Side chain dynamics were obtained by fitting the deuterium ssNMR line shape to specific motional models. Through the combined use of SFG and ssNMR, the dynamic trends observed for individual side chains by ssNMR have been correlated with side chain orientation relative to the PS surface as determined by SFG. This combination provides a more complete and quantitative picture of the structure, orientation, and dynamics of these surface-adsorbed peptides than could be obtained if either technique were used separately. PMID:20628016

Combined single crystal polarized XAFS and XRD at high pressure: probing the interplay between lattice distortions and electronic order at multiple length scales in high T c cuprates

DOE PAGES

Fabbris, G.; Hücker, M.; Gu, G. D.; ...

2016-07-14

Some of the most exotic material properties derive from electronic states with short correlation length (~10-500 Å), suggesting that the local structural symmetry may play a relevant role in their behavior. In this study, we discuss the combined use of polarized x-ray absorption fine structure and x-ray diffraction at high pressure as a powerful method to tune and probe structural and electronic orders at multiple length scales. Besides addressing some of the technical challenges associated with such experiments, we illustrate this approach with results obtained in the cuprate La 1.875Ba 0.125CuO 4, in which the response of electronic order tomore » pressure can only be understood by probing the structure at the relevant length scales.« less

Preentry communication design elements for outer planets atmospheric entry probe

NASA Technical Reports Server (NTRS)

1976-01-01

Four related tasks are discussed for data transmission from a probe prior to entering the atmosphere of Jupiter to an orbiting spacecraft in a trajectory past the planet: (1) link analysis and design; (2) system conceptual design; (3) Doppler measurement analysis; and (4) an electronically despun antenna. For tasks 1, 3, and 4, an analytical approach was developed and combined with computational capability available to produce quantitative results corresponding to requirements and constraints given by NASA, ARC. One constraint having a major impact on the numerical results of the link analysis was the assumption of a nonsteerable antenna on a spinning orbiter. Other constraints included the interplanetary trajectory and the approach trajectory. Because the Jupiter Orbiter Probe (JOP) program is currently in a state of evolution, all requirements and constraints applied during this study are subject to change. However, the relationships of parameters as developed will remain valid and will aid in planning Jupiter missions.

User oriented end-station on VUV pump-probe magneto-optical ellipsometry at ELI beamlines

NASA Astrophysics Data System (ADS)

Espinoza, Shirly; Neuber, Gerd; Brooks, Christopher D.; Besner, Bastian; Hashemi, Maryam; Rübhausen, Michael; Andreasson, Jakob

2017-11-01

A state of the art ellipsometer for user operations is being implemented at ELI Beamlines in Prague, Czech Republic. It combines three of the most promising and exotic forms of ellipsometry: VUV, pump-probe and magneto-optical ellipsometry. This new ellipsometer covers a spectral operational range from the NIR up to the VUV, with high through-put between 1 and 40 eV. The ellipsometer also allows measurements of magneto-optical spectra with a 1 kHz switchable magnetic field of up to 1.5 T across the sample combining ellipsometry and Kerr spectroscopy measurements in an unprecedented spectral range. This form of generalized ellipsometry enables users to address diagonal and off-diagonal components of the dielectric tensor within one measurement. Pump-probe measurements enable users to study the dynamic behaviour of the dielectric tensor in order to resolve the time-domain phenomena in the femto to 100 ns range.

Bioresponsive probes for molecular imaging: concepts and in vivo applications.

PubMed

van Duijnhoven, Sander M J; Robillard, Marc S; Langereis, Sander; Grüll, Holger

2015-01-01

Molecular imaging is a powerful tool to visualize and characterize biological processes at the cellular and molecular level in vivo. In most molecular imaging approaches, probes are used to bind to disease-specific biomarkers highlighting disease target sites. In recent years, a new subset of molecular imaging probes, known as bioresponsive molecular probes, has been developed. These probes generally benefit from signal enhancement at the site of interaction with its target. There are mainly two classes of bioresponsive imaging probes. The first class consists of probes that show direct activation of the imaging label (from "off" to "on" state) and have been applied in optical imaging and magnetic resonance imaging (MRI). The other class consists of probes that show specific retention of the imaging label at the site of target interaction and these probes have found application in all different imaging modalities, including photoacoustic imaging and nuclear imaging. In this review, we present a comprehensive overview of bioresponsive imaging probes in order to discuss the various molecular imaging strategies. The focus of the present article is the rationale behind the design of bioresponsive molecular imaging probes and their potential in vivo application for the detection of endogenous molecular targets in pathologies such as cancer and cardiovascular disease. Copyright © 2015 John Wiley & Sons, Ltd.

Long-term luminescence of sensibilizers in tissues at the conditions of oxygen deficiency due to photodynamic effect

NASA Astrophysics Data System (ADS)

Ishemgulov, A. T.; Letuta, S. N.; Pashkevich, S. N.; Alidzhanov, E. K.; Lantukh, Yu. D.

2017-11-01

Long-term luminescence of organic dyes (xanthene dyes, halogen substituted fluoroscein) was used for an in vitro study of the photodynamic effect of exogenic probes in malignant tumors and healthy tissues of mice. It is shown that the photodynamic activity of oxygen and the dynamics of its concentration in tissues can be estimated from the delayed fluorescence of exogenic probes caused by singlet-triplet annihilation of singlet oxygen and excited triplet states of the molecules of photosensitizer dyes. It is found that quenching of long-term luminescence of photosensitizers significantly differs in tumors and normal tissues.

Ultrafast measurements of chlorine dioxide photochemistry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ludowise, P.D.

Time-resolved mass spectrometry and time-resolved photoelectron spectroscopy are used to study the ultrafast photodissociation dynamics of chlorine dioxide, an important constituent in stratospheric ozone depletion. Chapter 1 introduces these pump/probe techniques, in which a femtosecond pump pulse excites a molecule to a dissociative state. At a later time, a second femtosecond probe pulse ionizes the molecule. The resulting mass and photoelectron spectra are acquired as a function of the delay between the pump and probe pulses, which follows the evolution of the molecule on the excited state. A comparison to other techniques used to study reaction dynamics is discussed. Chaptermore » 2 includes a detailed description of the design and construction of the experimental apparatus, which consists of a femtosecond laser system, a molecular beam time-of-flight spectrometer, and a data acquisition system. The time-of-flight spectrometer is specifically designed to have a short flight distance to maximize the photoelectron collection efficiency without degrading the resolution, which is limited by the bandwidth of the femtosecond laser system. Typical performance of the apparatus is demonstrated in a study of the time-resolved photoelectron spectroscopy of nitric oxide. The results of the time-resolved mass spectrometry experiments of chlorine dioxide are presented in Chapter 3. Upon excitation to the A {sup 2}A{sub 2} state near 3.2 eV, the molecule dissociates through an indirect two-step mechanism. The direct dissociation channel has been predicted to be open, but is not observed. A quantum beat is observed in the OClO{sup +} species, which is described as a vibrational coherence of the optically prepared A {sup 2}A{sub 2} state. Chapter 4 presents the results of the time-resolved photoelectron experiments of chlorine dioxide. At short delay time, the quantum beat of the OClO{sup +} species is observed in the X {sup 1}A{sub 1} state of the ion. At infinite delay, the signal is dominated by the ClO{sup +} ion, observed in a variety of electronic states. The photoelectron data is shown to support the indirect two-step dissociation mechanism derived from the mass results. Conclusions of the mass and photoelectron results are discussed in context of the stratospheric ozone depletion problem.« less

Studies in Intelligence. Volume 56, Number 1

DTIC Science & Technology

2012-03-01

Leap Forward) Japan (post- Fukushima Daiichi ) Burma (outer provinces) Cambodia (post-Khmer Rouge) On State Instability 18 Studies in Intelligence Vol...March 2012) Center for the Study of Intelligence Products or Outputs?: Probing the Implications of Changing the Outputs of Intelligence Following Trends...Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a

Preparation and Characterization of Fluorescent Derivatives of Lysozyme

NASA Technical Reports Server (NTRS)

Smith, Lori; Pusey, Marc

1998-01-01

Fluorescence is one of the most versatile and powerful tools for the study of macromolecules. However, its use in macromolecular crystal growth studies is hampered by the necessity of preparing fluorescent derivatives where the probe does not markedly affect the crystal packing. Alternatively, one can prepare derivatives of limited utility if it is known that they will not affect the specific goals of a given study. We have prepared a number of fluorescent derivatives of chicken egg white lysozyme, covalently attaching fluorescent probes to two different sites on the protein molecule. The first site is the side chain carboxyl group of ASP 101. Amine containing probes such as lucifer yellow, cascade blue, and 5- (2-aminoethyl) aminonapthalene-l-sulfonic acid (EDANS) have been attached using a carbodiimide coupling procedure. ASP 101 lies within the active site cleft, and it is believed that the probes are "buried" within that cleft. This is supported by the fact that all such derivatives have been found to crystallize, with the crystals being fluorescent. Tetragonal crystals of the lucifer yellow derivative have been found to diffract to at least 1.9 A resolution. X-ray diffraction data has been acquired and we are now working on the structure of this derivative. The second group of derivatives is to the N-terminal amine group. The derivatization reaction is performed by using a succinimidyl ester of the probe to be attached. Fluorescent probes such as pyrene acetic acid, 5-carboxyfluorescein, and Oregon green have been attached to this site. We have had little success in crystallizing these derivatives, probably because this site is part of the contact region between the 43 helix chains. However, these sites do not interfere with formation of the 43 helices and the derivatives are suitable for study of their formation in solution. The derivatives are being characterized by steady state and lifetime fluorescence methods, and the presentation will discuss these results.

Pinch-off mechanism in double-lateral-gate junctionless transistors fabricated by scanning probe microscope based lithography

PubMed Central

Dehzangi, Arash; Abedini, Alam; Abdullah, Ahmad Makarimi; Saion, Elias; Hutagalung, Sabar D; Hamidon, Mohd N; Hassan, Jumiah

2012-01-01

Summary A double-lateral-gate p-type junctionless transistor is fabricated on a low-doped (1015) silicon-on-insulator wafer by a lithography technique based on scanning probe microscopy and two steps of wet chemical etching. The experimental transfer characteristics are obtained and compared with the numerical characteristics of the device. The simulation results are used to investigate the pinch-off mechanism, from the flat band to the off state. The study is based on the variation of the carrier density and the electric-field components. The device is a pinch-off transistor, which is normally in the on state and is driven into the off state by the application of a positive gate voltage. We demonstrate that the depletion starts from the bottom corner of the channel facing the gates and expands toward the center and top of the channel. Redistribution of the carriers due to the electric field emanating from the gates creates an electric field perpendicular to the current, toward the bottom of the channel, which provides the electrostatic squeezing of the current. PMID:23365794

On the difference between breakdown and quench voltages of argon plasma and its relation to 4p–4s atomic state transitions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Forati, Ebrahim, E-mail: forati@ieee.org; Piltan, Shiva; Sievenpiper, Dan, E-mail: dsievenpiper@ucsd.edu

Using a relaxation oscillator circuit, breakdown (V{sub BD}) and quench (V{sub Q}) voltages of a DC discharge microplasma between two needle probes are measured. High resolution modified Paschen curves are obtained for argon microplasmas including a quench voltage curve representing the voltage at which the plasma turns off. It is shown that for a point to point microgap (e.g., the microgap between two needle probes) which describes many realistic microdevices, neither Paschen's law applies nor field emission is noticeable. Although normally V{sub BD} > V{sub Q,} it is observed that depending on environmental parameters of argon, such as pressure and the drivingmore » circuitry, plasma can exist in a different state with equal V{sub BD} and V{sub Q.} Using emission line spectroscopy, it is shown that V{sub BD} and V{sub Q} are equal if the atomic excitation by the electric field dipole moment dominantly leads to one of the argon's metastable states (4P{sub 5} in our study)« less

125Te NMR Probes of Tellurium Oxide Crystals: Shielding-Structure Correlations.

PubMed

Garaga, Mounesha N; Werner-Zwanziger, Ulrike; Zwanziger, Josef W

2018-01-16

The local environments around tellurium atoms in a series of tellurium oxide crystals were probed by 125 Te solid-state NMR spectroscopy. Crystals with distinct TeO n units (n from 3 to 6), including Na 2 TeO 3 , α-TeO 2 and γ-TeO 2 , Te 2 O(PO 4 ) 2 , K 3 LaTe 2 O 9 , BaZnTe 2 O 7 , and CsYTe 3 O 8 were studied. The latter four were synthesized through a solid-state process. X-ray diffraction was used to confirm the successful syntheses. The 125 Te chemical shift was found to exhibit a strong linear correlation with the Te coordination number. The 125 Te chemical-shift components (δ 11 , δ 22 , and δ 33 ) of the TeO 4 units were further correlated to the O-Te-O-bond angles. With the aid of 125 Te NMR, it is likely that these relations can be used to estimate the coordination states of Te atoms in unknown Te crystals and glasses.

Control of cerium oxidation state through metal complex secondary structures

DOE PAGES

Levin, Jessica R.; Dorfner, Walter L.; Carroll, Patrick J.; ...

2015-08-11

A series of alkali metal cerium diphenylhydrazido complexes, M x(py) y[Ce(PhNNPh) 4], M = Li, Na, and K, x = 4 (Li and Na) or 5 (K), and y = 4 (Li), 8 (Na), or 7 (K), were synthesized to probe how a secondary coordination sphere would modulate electronic structures at a cerium cation. The resulting electronic structures of the heterobimetallic cerium diphenylhydrazido complexes were found to be strongly dependent on the identity of the alkali metal cations. When M = Li + or Na +, the cerium(III) starting material was oxidized with concomitant reduction of 1,2-diphenylhydrazine to aniline. Reductionmore » of 1,2-diphenylhydrazine was not observed when M = K +, and the complex remained in the cerium(III) oxidation state. Oxidation of the cerium(III) diphenylhydrazido complex to the Ce( IV) diphenylhydrazido one was achieved through a simple cation exchange reaction of the alkali metals. As a result, UV-Vis spectroscopy, FTIR spectroscopy, electrochemistry, magnetic susceptibility, and DFT studies were used to probe the oxidation state and the electronic changes that occurred at the metal centre.« less

Spectral response of crystalline acetanilide and N -methylacetamide: Vibrational self-trapping in hydrogen-bonded crystals

NASA Astrophysics Data System (ADS)

Edler, Julian; Hamm, Peter

2004-06-01

Femtosecond pump-probe and Fourier transform infrared spectroscopy is applied to compare the spectral response of the amide I band and the NH-stretching band of acetanilide (ACN) and N -methylacetamide (NMA), as well as their deuterated derivatives. Both molecules form hydrogen-bonded molecular crystals that are regarded to be model systems for polypeptides and proteins. The amide I bands of both ACN and NMA show a temperature-dependent sideband, while the NH bands are accompanied by a sequence of equidistantly spaced satellite peaks. These spectral anomalies are interpreted as a signature of vibrational self-trapping. Two different types of states can be identified in both crystals in the pump-probe signal: a delocalized free-exciton state and a set of localized self-trapped states. The phonons that mediate self-trapping in ACN and deuterated ACN are identified by their temperature dependence, confirming our previous results. The study shows that the substructure of the NH band in NMA (amide A and amide B bands) originates, at least partly, from vibrational self-trapping and not, as often assumed, from a Fermi resonance.

Assessment of bilayer silicene to probe as quantum spin and valley Hall effect

NASA Astrophysics Data System (ADS)

Rehman, Majeed Ur; Qiao, Zhenhua

2018-02-01

Silicene takes precedence over graphene due to its buckling type structure and strong spin orbit coupling. Motivated by these properties, we study the silicene bilayer in the presence of applied perpendicular electric field and intrinsic spin orbit coupling to probe as quantum spin/valley Hall effect. Using analytical approach, we calculate the spin Chern-number of bilayer silicene and then compare it with monolayer silicene. We reveal that bilayer silicene hosts double spin Chern-number as compared to single layer silicene and therefore accordingly has twice as many edge states in contrast to single layer silicene. In addition, we investigate the combined effect of intrinsic spin orbit coupling and the external electric field, we find that bilayer silicene, likewise single layer silicene, goes through a phase transitions from a quantum spin Hall state to a quantum valley Hall state when the strength of the applied electric field exceeds the intrinsic spin orbit coupling strength. We believe that the results and outcomes obtained for bilayer silicene are experimentally more accessible as compared to bilayer graphene, because of strong SO coupling in bilayer silicene.

Spin filtering in a double quantum dot device: Numerical renormalization group study of the internal structure of the Kondo state

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vernek, E.; Instituto de Física de São Carlos, Universidade de São Paulo, São Carlos-SP 13560-970; Büsser, C. A.

2014-03-31

A double quantum dot device, connected to two channels that only interact through interdot Coulomb repulsion, is analyzed using the numerical renormalization group technique. Using a two-impurity Anderson model, and realistic parameter values [S. Amasha, A. J. Keller, I. G. Rau, A. Carmi, J. A. Katine, H. Shtrikman, Y. Oreg, and D. Goldhaber-Gordon, Phys. Rev. Lett. 110, 046604 (2013)], it is shown that, by applying a moderate magnetic field and independently adjusting the gate potential of each quantum dot at half-filling, a spin-orbital SU(2) Kondo state can be achieved where the Kondo resonance originates from spatially separated parts of themore » device. Our results clearly link this spatial separation effect to currents with opposing spin polarizations in each channel, i.e., the device acts as a spin filter. In addition, an experimental probe of this polarization effect is suggested, pointing to the exciting possibility of experimentally probing the internal structure of an SU(2) Kondo state.« less

Kinetics model for the wavelength-dependence of excited-state dynamics of hetero-FRET sensors

NASA Astrophysics Data System (ADS)

Schwarz, Jacob; Leighton, Ryan; Leopold, Hannah J.; Currie, Megan; Boersma, Arnold J.; Sheets, Erin D.; Heikal, Ahmed A.

2017-08-01

Foerster (or fluorescence) resonance energy transfer (FRET) is a powerful tool for investigating protein-protein interactions, in both living cells and in controlled environments. A typical hetero-FRET pair consists of a donor and acceptor tethered together with a linker. The corresponding energy transfer efficiency of a hetero-FRET pair probe depends upon the donor-acceptor distance, relative dipole orientation, and spectral overlap. Because of the sensitivity of the energy transfer efficiency on the donor-acceptor distance, FRET is often referred to as a "molecular ruler". Time-resolved fluorescence approach for measuring the excited-state lifetime of the donor and acceptor emissions is one of the most reliable approaches for quantitative assessment of the energy transfer efficiency in hetero-FRET pairs. In this contribution, we provide an analytical kinetics model that describes the excited-state depopulation of a FRET probe as a means to predicts the time-resolved fluorescence profile as a function of excitation and detection wavelengths. In addition, we used this developed kinetics model to simulate the time-dependence of the excited-state population of both the donor and acceptor. These results should serve as a guide for our ongoing studies of newly developed hetero-FRET sensors (mCerulean3-linker-mCitrine) that are designed specifically for in vivo studies of macromolecular crowding. The same model is applicable to other FRET pairs with the careful consideration of their steady-state spectroscopy and the experimental design for wavelength- dependence of the fluorescence lifetime measurements.

Continuous-variable quantum probes for structured environments

NASA Astrophysics Data System (ADS)

Bina, Matteo; Grasselli, Federico; Paris, Matteo G. A.

2018-01-01

We address parameter estimation for structured environments and suggest an effective estimation scheme based on continuous-variables quantum probes. In particular, we investigate the use of a single bosonic mode as a probe for Ohmic reservoirs, and obtain the ultimate quantum limits to the precise estimation of their cutoff frequency. We assume the probe prepared in a Gaussian state and determine the optimal working regime, i.e., the conditions for the maximization of the quantum Fisher information in terms of the initial preparation, the reservoir temperature, and the interaction time. Upon investigating the Fisher information of feasible measurements, we arrive at a remarkable simple result: homodyne detection of canonical variables allows one to achieve the ultimate quantum limit to precision under suitable, mild, conditions. Finally, upon exploiting a perturbative approach, we find the invariant sweet spots of the (tunable) characteristic frequency of the probe, able to drive the probe towards the optimal working regime.

Development and Application of Wide Bandwidth Magneto-Resistive Sensor Based Eddy Current Probe

NASA Technical Reports Server (NTRS)

Wincheski, Russell A.; Simpson, John

2010-01-01

The integration of magneto-resistive sensors into eddy current probes can significantly expand the capabilities of conventional eddy current nondestructive evaluation techniques. The room temperature solid-state sensors have typical bandwidths in the megahertz range and resolutions of tens of microgauss. The low frequency sensitivity of magneto-resistive sensors has been capitalized upon in previous research to fabricate very low frequency eddy current sensors for deep flaw detection in multilayer conductors. In this work a modified probe design is presented to expand the capabilities of the device. The new probe design incorporates a dual induction source enabling operation from low frequency deep flaw detection to high frequency high resolution near surface material characterization. Applications of the probe for the detection of localized near surface conductivity anomalies are presented. Finite element modeling of the probe is shown to be in good agreement with experimental measurements.

Solid-state electrochemistry on the nanometer and atomic scales: the scanning probe microscopy approach

PubMed Central

Strelcov, Evgheni; Yang, Sang Mo; Jesse, Stephen; Balke, Nina; Vasudevan, Rama K.; Kalinin, Sergei V.

2016-01-01

Energy technologies of the 21st century require understanding and precise control over ion transport and electrochemistry at all length scales – from single atoms to macroscopic devices. This short review provides a summary of recent works dedicated to methods of advanced scanning probe microscopy for probing electrochemical transformations in solids at the meso-, nano- and atomic scales. Discussion presents advantages and limitations of several techniques and a wealth of examples highlighting peculiarities of nanoscale electrochemistry. PMID:27146961

Characterization of magnetic force microscopy probe tip remagnetization for measurements in external in-plane magnetic fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weis, Tanja; Engel, Dieter; Ehresmann, Arno

2008-12-15

A quantitative analysis of magnetic force microscopy (MFM) images taken in external in-plane magnetic fields is difficult because of the influence of the magnetic field on the magnetization state of the magnetic probe tip. We prepared calibration samples by ion bombardment induced magnetic patterning with a topographically flat magnetic pattern magnetically stable in a certain external magnetic field range for a quantitative characterization of the MFM probe tip magnetization in point-dipole approximation.

Campanile Near-Field Probes Fabricated by Nanoimprint Lithography on the Facet of an Optical Fiber

DOE PAGES

Calafiore, Giuseppe; Koshelev, Alexander; Darlington, Thomas P.; ...

2017-05-10

One of the major challenges to the widespread adoption of plasmonic and nano-optical devices in real-life applications is the difficulty to mass-fabricate nano-optical antennas in parallel and reproducible fashion, and the capability to precisely place nanoantennas into devices with nanometer-scale precision. In this study, we present a solution to this challenge using the state-of-the-art ultraviolet nanoimprint lithography (UV-NIL) to fabricate functional optical transformers onto the core of an optical fiber in a single step, mimicking the 'campanile' near-field probes. Imprinted probes were fabricated using a custom-built imprinter tool with co-axial alignment capability with sub < 100 nm position accuracy, followedmore » by a metallization step. Scanning electron micrographs confirm high imprint fidelity and precision with a thin residual layer to facilitate efficient optical coupling between the fiber and the imprinted optical transformer. The imprinted optical transformer probe was used in an actual NSOM measurement performing hyperspectral photoluminescence mapping of standard fluorescent beads. The calibration scans confirmed that imprinted probes enable sub-diffraction limited imaging with a spatial resolution consistent with the gap size. This novel nano-fabrication approach promises a low-cost, high-throughput, and reproducible manufacturing of advanced nano-optical devices.« less

Campanile Near-Field Probes Fabricated by Nanoimprint Lithography on the Facet of an Optical Fiber

DOE Office of Scientific and Technical Information (OSTI.GOV)

Calafiore, Giuseppe; Koshelev, Alexander; Darlington, Thomas P.

One of the major challenges to the widespread adoption of plasmonic and nano-optical devices in real-life applications is the difficulty to mass-fabricate nano-optical antennas in parallel and reproducible fashion, and the capability to precisely place nanoantennas into devices with nanometer-scale precision. In this study, we present a solution to this challenge using the state-of-the-art ultraviolet nanoimprint lithography (UV-NIL) to fabricate functional optical transformers onto the core of an optical fiber in a single step, mimicking the 'campanile' near-field probes. Imprinted probes were fabricated using a custom-built imprinter tool with co-axial alignment capability with sub < 100 nm position accuracy, followedmore » by a metallization step. Scanning electron micrographs confirm high imprint fidelity and precision with a thin residual layer to facilitate efficient optical coupling between the fiber and the imprinted optical transformer. The imprinted optical transformer probe was used in an actual NSOM measurement performing hyperspectral photoluminescence mapping of standard fluorescent beads. The calibration scans confirmed that imprinted probes enable sub-diffraction limited imaging with a spatial resolution consistent with the gap size. This novel nano-fabrication approach promises a low-cost, high-throughput, and reproducible manufacturing of advanced nano-optical devices.« less

Dynamic analysis of apoptosis using cyanine SYTO probes: From classical to microfluidic cytometry

PubMed Central

Wlodkowic, Donald; Skommer, Joanna; Faley, Shannon; Darzynkiewicz, Zbigniew; Cooper, Jonathan M.

2013-01-01

Cell death is a stochastic process, often initiated and/or executed in a multi-pathway/multi-organelle fashion. Therefore, high-throughput single-cell analysis platforms are required to provide detailed characterization of kinetics and mechanisms of cell death in heterogeneous cell populations. However, there is still a largely unmet need for inert fluorescent probes, suitable for prolonged kinetic studies. Here, we compare the use of innovative adaptation of unsymmetrical SYTO dyes for dynamic real-time analysis of apoptosis in conventional as well as microfluidic chip-based systems. We show that cyanine SYTO probes allow non-invasive tracking of intracellular events over extended time. Easy handling and “stain–no wash” protocols open up new opportunities for high-throughput analysis and live-cell sorting. Furthermore, SYTO probes are easily adaptable for detection of cell death using automated microfluidic chip-based cytometry. Overall, the combined use of SYTO probes and state-of-the-art Lab-on-a-Chip platform emerges as a cost effective solution for automated drug screening compared to conventional Annexin V or TUNEL assays. In particular, it should allow for dynamic analysis of samples where low cell number has so far been an obstacle, e.g. primary cancer stems cells or circulating minimal residual tumors. PMID:19298813

Fluorogenic PNA probes

PubMed Central

2018-01-01

Fluorogenic oligonucleotide probes that can produce a change in fluorescence signal upon binding to specific biomolecular targets, including nucleic acids as well as non-nucleic acid targets, such as proteins and small molecules, have applications in various important areas. These include diagnostics, drug development and as tools for studying biomolecular interactions in situ and in real time. The probes usually consist of a labeled oligonucleotide strand as a recognition element together with a mechanism for signal transduction that can translate the binding event into a measurable signal. While a number of strategies have been developed for the signal transduction, relatively little attention has been paid to the recognition element. Peptide nucleic acids (PNA) are DNA mimics with several favorable properties making them a potential alternative to natural nucleic acids for the development of fluorogenic probes, including their very strong and specific recognition and excellent chemical and biological stabilities in addition to their ability to bind to structured nucleic acid targets. In addition, the uncharged backbone of PNA allows for other unique designs that cannot be performed with oligonucleotides or analogues with negatively-charged backbones. This review aims to introduce the principle, showcase state-of-the-art technologies and update recent developments in the areas of fluorogenic PNA probes during the past 20 years. PMID:29507634

Dynamic Pressure Probes Developed for Supersonic Flow-Field Measurements

NASA Technical Reports Server (NTRS)

Porro, A. Robert

2001-01-01

A series of dynamic flow-field pressure probes were developed for use in large-scale supersonic wind tunnels at the NASA Glenn Research Center. These flow-field probes include pitot and static pressure probes that can capture fast-acting flow-field pressure transients occurring on a millisecond timescale. The pitot and static probes can be used to determine local Mach number time histories during a transient event. The flow-field pressure probe contains four major components: 1) Static pressure aerodynamic tip; 2) Pressure-sensing cartridge assembly; 3) Pitot pressure aerodynamic tip; 4) Mounting stem. This modular design allows for a variety of probe tips to be used for a specific application. Here, the focus is on flow-field pressure measurements in supersonic flows, so we developed a cone-cylinder static pressure tip and a pitot pressure tip. Alternatively, probe tips optimized for subsonic and transonic flows could be used with this design. The pressure-sensing cartridge assembly allows the simultaneous measurement of steady-state and transient pressure which allows continuous calibration of the dynamic pressure transducer.

Transient diffraction grating measurements of molecular diffusion in the undergraduate laboratory

NASA Astrophysics Data System (ADS)

Spiegel, Daniel R.; Tuli, Santona

2011-07-01

Diffusion is a central process in many biological, chemical, and physical systems. We describe an experiment that employs the interference of laser beams to allow the measurement of molecular diffusion on submillimeter length scales. The interference fringes of two intersecting pump beams within a dye solution create a sinusoidal distribution of long-lived molecular excited states. A third probe beam is incident at a wavelength at which the indices of refraction of the ground and excited states are different, so the probe beam diffracts from the spatially periodic excited-state pattern. After the pump beams are switched off, the excited-state periodicity washes out as the system diffuses back to equilibrium. The molecular diffusion constant is obtained from the rate constant of the exponential decay of the diffracted beam. It is also possible to measure the excited-state lifetime.

Exploring the Supervision Experiences of Student Affairs Mid-Level Leaders in Catholic Higher Education

ERIC Educational Resources Information Center

Wenzel, Dorothy Ann

2013-01-01

This qualitative study examined the supervision experiences of 17 student affairs department directors at six Catholic colleges and universities in the Northeast and Mid-Atlantic regions of the United States. The study focused on the supervision and management skills needed by mid-level managers, and probed if and how they acquired those skills.…

Reward devaluation: Dot-probe meta-analytic evidence of avoidance of positive information in depressed persons.

PubMed

Winer, E Samuel; Salem, Taban

2016-01-01

Cognitive theories of depression and anxiety have traditionally emphasized the role of attentional biases in the processing of negative information. The dot-probe task has been widely used to study this phenomenon. Recent findings suggest that biased processing of positive information might also be an important aspect of developing psychopathological symptoms. However, despite some evidence suggesting persons with symptoms of depression and anxiety may avoid positive information, many dot-probe studies have produced null findings. The present review used conventional and novel meta-analytic methods to evaluate dot-probe attentional biases away from positive information and, for comparison, toward negative information, in depressed and anxious individuals. Results indicated that avoidance of positive information is a real effect exhibiting substantial evidential value among persons experiencing psychopathology, with individuals evidencing primary symptoms of depression clearly demonstrating this effect. Different theoretical explanations for these findings are evaluated, including those positing threat-processing structures, even-handedness, self-regulation, and reward devaluation, with the novel theory of reward devaluation emphasized and expanded. These novel findings and theory suggest that avoidance of prospective reward helps to explain the cause and sustainability of depressed states. Suggestions for future research and methodological advances are discussed. (c) 2015 APA, all rights reserved).

Energy-Looping Nanoparticles: Harnessing Excited-State Absorption for Deep-Tissue Imaging.

PubMed

Levy, Elizabeth S; Tajon, Cheryl A; Bischof, Thomas S; Iafrati, Jillian; Fernandez-Bravo, Angel; Garfield, David J; Chamanzar, Maysamreza; Maharbiz, Michel M; Sohal, Vikaas S; Schuck, P James; Cohen, Bruce E; Chan, Emory M

2016-09-27

Near infrared (NIR) microscopy enables noninvasive imaging in tissue, particularly in the NIR-II spectral range (1000-1400 nm) where attenuation due to tissue scattering and absorption is minimized. Lanthanide-doped upconverting nanocrystals are promising deep-tissue imaging probes due to their photostable emission in the visible and NIR, but these materials are not efficiently excited at NIR-II wavelengths due to the dearth of lanthanide ground-state absorption transitions in this window. Here, we develop a class of lanthanide-doped imaging probes that harness an energy-looping mechanism that facilitates excitation at NIR-II wavelengths, such as 1064 nm, that are resonant with excited-state absorption transitions but not ground-state absorption. Using computational methods and combinatorial screening, we have identified Tm(3+)-doped NaYF4 nanoparticles as efficient looping systems that emit at 800 nm under continuous-wave excitation at 1064 nm. Using this benign excitation with standard confocal microscopy, energy-looping nanoparticles (ELNPs) are imaged in cultured mammalian cells and through brain tissue without autofluorescence. The 1 mm imaging depths and 2 μm feature sizes are comparable to those demonstrated by state-of-the-art multiphoton techniques, illustrating that ELNPs are a promising class of NIR probes for high-fidelity visualization in cells and tissue.

Orbital-specific mapping of the ligand exchange dynamics of Fe(CO)5 in solution.

PubMed

Wernet, Ph; Kunnus, K; Josefsson, I; Rajkovic, I; Quevedo, W; Beye, M; Schreck, S; Grübel, S; Scholz, M; Nordlund, D; Zhang, W; Hartsock, R W; Schlotter, W F; Turner, J J; Kennedy, B; Hennies, F; de Groot, F M F; Gaffney, K J; Techert, S; Odelius, M; Föhlisch, A

2015-04-02

Transition-metal complexes have long attracted interest for fundamental chemical reactivity studies and possible use in solar energy conversion. Electronic excitation, ligand loss from the metal centre, or a combination of both, creates changes in charge and spin density at the metal site that need to be controlled to optimize complexes for photocatalytic hydrogen production and selective carbon-hydrogen bond activation. An understanding at the molecular level of how transition-metal complexes catalyse reactions, and in particular of the role of the short-lived and reactive intermediate states involved, will be critical for such optimization. However, suitable methods for detailed characterization of electronic excited states have been lacking. Here we show, with the use of X-ray laser-based femtosecond-resolution spectroscopy and advanced quantum chemical theory to probe the reaction dynamics of the benchmark transition-metal complex Fe(CO)5 in solution, that the photo-induced removal of CO generates the 16-electron Fe(CO)4 species, a homogeneous catalyst with an electron deficiency at the Fe centre, in a hitherto unreported excited singlet state that either converts to the triplet ground state or combines with a CO or solvent molecule to regenerate a penta-coordinated Fe species on a sub-picosecond timescale. This finding, which resolves the debate about the relative importance of different spin channels in the photochemistry of Fe(CO)5 (refs 4, 16 - 20), was made possible by the ability of femtosecond X-ray spectroscopy to probe frontier-orbital interactions with atom specificity. We expect the method to be broadly applicable in the chemical sciences, and to complement approaches that probe structural dynamics in ultrafast processes.

Orbital-specific mapping of the ligand exchange dynamics of Fe(CO)5 in solution

NASA Astrophysics Data System (ADS)

Wernet, Ph.; Kunnus, K.; Josefsson, I.; Rajkovic, I.; Quevedo, W.; Beye, M.; Schreck, S.; Grübel, S.; Scholz, M.; Nordlund, D.; Zhang, W.; Hartsock, R. W.; Schlotter, W. F.; Turner, J. J.; Kennedy, B.; Hennies, F.; de Groot, F. M. F.; Gaffney, K. J.; Techert, S.; Odelius, M.; Föhlisch, A.

2015-04-01

Transition-metal complexes have long attracted interest for fundamental chemical reactivity studies and possible use in solar energy conversion. Electronic excitation, ligand loss from the metal centre, or a combination of both, creates changes in charge and spin density at the metal site that need to be controlled to optimize complexes for photocatalytic hydrogen production and selective carbon-hydrogen bond activation. An understanding at the molecular level of how transition-metal complexes catalyse reactions, and in particular of the role of the short-lived and reactive intermediate states involved, will be critical for such optimization. However, suitable methods for detailed characterization of electronic excited states have been lacking. Here we show, with the use of X-ray laser-based femtosecond-resolution spectroscopy and advanced quantum chemical theory to probe the reaction dynamics of the benchmark transition-metal complex Fe(CO)5 in solution, that the photo-induced removal of CO generates the 16-electron Fe(CO)4 species, a homogeneous catalyst with an electron deficiency at the Fe centre, in a hitherto unreported excited singlet state that either converts to the triplet ground state or combines with a CO or solvent molecule to regenerate a penta-coordinated Fe species on a sub-picosecond timescale. This finding, which resolves the debate about the relative importance of different spin channels in the photochemistry of Fe(CO)5 (refs 4, 16,17,18,19 and 20), was made possible by the ability of femtosecond X-ray spectroscopy to probe frontier-orbital interactions with atom specificity. We expect the method to be broadly applicable in the chemical sciences, and to complement approaches that probe structural dynamics in ultrafast processes.

Rational Design of in Vivo Tau Tangle-Selective Near-Infrared Fluorophores: Expanding the BODIPY Universe.

PubMed

Verwilst, Peter; Kim, Hye-Ri; Seo, Jinho; Sohn, Nak-Won; Cha, Seung-Yun; Kim, Yeongmin; Maeng, Sungho; Shin, Jung-Won; Kwak, Jong Hwan; Kang, Chulhun; Kim, Jong Seung

2017-09-27

The elucidation of the cause of Alzheimer's disease remains one of the greatest questions in neurodegenerative research. The lack of highly reliable low-cost sensors to study the structural changes in key proteins during the progression of the disease is a contributing factor to this lack of insight. In the current work, we describe the rational design and synthesis of two fluorescent BODIPY-based probes, named Tau 1 and Tau 2. The probes were evaluated on the molecular surface formed by a fibril of the PHF6 ( 306 VQIVYK 311 ) tau fragment using molecular docking studies to provide a potential molecular model to rationalize the selectivity of the new probes as compared to a homologous Aβ-selective probe. The probes were synthesized in a few steps from commercially available starting products and could thus prove to be highly cost-effective. We demonstrated the excellent photophysical properties of the dyes, such as a large Stokes shift and emission in the near-infrared window of the electromagnetic spectrum. The probes demonstrated a high selectivity for self-assembled microtubule-associated protein tau (Tau protein), in both solution and cell-based experiments. Moreover, the administration to an acute murine model of tauopathy clearly revealed the staining of self-assembled hyperphosphorylated tau protein in pathologically relevant hippocampal brain regions. Tau 1 demonstrated efficient blood-brain barrier penetrability and demonstrated a clear selectivity for tau tangles over Aβ plaques, as well as the capacity for in vivo imaging in a transgenic mouse model. The current work could open up avenues for the cost-effective monitoring of the tau protein aggregation state in animal models as well as tissue staining. Furthermore, these fluorophores could serve as the basis for the development of clinically relevant sensors, for example based on PET imaging.

DHA-fluorescent probe is sensitive to membrane order and reveals molecular adaptation of DHA in ordered lipid microdomains☆

PubMed Central

Teague, Heather; Ross, Ron; Harris, Mitchel; Mitchell, Drake C.; Shaikh, Saame Raza

2012-01-01

Docosahexaenoic acid (DHA) disrupts the size and order of plasma membrane lipid microdomains in vitro and in vivo. However, it is unknown how the highly disordered structure of DHA mechanistically adapts to increase the order of tightly packed lipid microdomains. Therefore, we studied a novel DHA-Bodipy fluorescent probe to address this issue. We first determined if the DHA-Bodipy probe localized to the plasma membrane of primary B and immortal EL4 cells. Image analysis revealed that DHA-Bodipy localized into the plasma membrane of primary B cells more efficiently than EL4 cells. We then determined if the probe detected changes in plasma membrane order. Quantitative analysis of time-lapse movies established that DHA-Bodipy was sensitive to membrane molecular order. This allowed us to investigate how DHA-Bodipy physically adapted to ordered lipid microdomains. To accomplish this, we employed steady-state and time-resolved fluorescence anisotropy measurements in lipid vesicles of varying composition. Similar to cell culture studies, the probe was highly sensitive to membrane order in lipid vesicles. Moreover, these experiments revealed, relative to controls, that upon incorporation into highly ordered microdomains, DHA-Bodipy underwent an increase in its fluorescence lifetime and molecular order. In addition, the probe displayed a significant reduction in its rotational diffusion compared to controls. Altogether, DHA-Bodipy was highly sensitive to membrane order and revealed for the first time that DHA, despite its flexibility, could become ordered with less rotational motion inside ordered lipid microdomains. Mechanistically, this explains how DHA acyl chains can increase order upon formation of lipid microdomains in vivo. PMID:22841541

Effect of electrostatic interaction on the location of molecular probe in polymer-surfactant supramolecular assembly: a solvent relaxation study.

PubMed

Singh, Prabhat K; Kumbhakar, Manoj; Pal, Haridas; Nath, Sukhendu

2008-07-03

Effect of electrostatic interaction on the location of a solubilized molecular probe with ionic character in a supramolecular assembly composed of a triblock copolymer, P123 ((ethylene oxide) 20-(propylene oxide) 70-(ethylene oxide) 20) and a cosurfactant cetyltrimethylammonium chloride (CTAC) in aqueous medium has been studied using steady-state and time-resolved fluorescence measurements. Coumarin-343 dye in its anionic form has been used as the molecular probe. In the absence of the surfactant, CTAC, the probe C343 prefers to reside at the surface region of the P123 micelle, showing a relatively less dynamic Stokes' shift, as a large part of the Stokes' shift is missed in the present measurements due to faster solvent relaxation at micellar surface region. As the concentration of CTAC is increased in the solution, the percentage of the total dynamic Stokes' shift observed from time-resolved measurements gradually increases until it reaches a saturation value. Observed results have been rationalized on the basis of the mixed micellar structure of the supramolecular assembly, where the hydrocarbon chain of the CTAC surfactant dissolves into the nonpolar poly(propylene oxide) (PPO) core of the P123 micelle and the positively charged headgroup of CTAC resides at the interfacial region between the central PPO core and the surrounding hydrated poly(ethylene oxide) (PEO) shell or the corona region. The electrostatic attraction between the anionic probe molecule and the positively charged surface of the PPO core developed by the presence of CTAC results in a gradual shift of the probe in the deeper region of the micellar corona region with an increase in the CTAC concentration, as clearly manifested from the solvation dynamics results.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Xiaoguang; McGuire, Michael A.; Chen, Yong P.

Topological insulators, with characteristic topological surface states, have emerged as a new state of matter with rich potentials for both fundamental physics and device applications. However, the experimental detection of the surface transport has been hampered by the unavoidable extrinsic conductivity associated with the bulk crystals. Here we show that a four-probe transport spectroscopy in a multi-probe scanning tunneling microscopy system can be used to differentiate conductivities from the surface states and the coexisting bulk states in topological insulators. We derive a scaling relation of measured resistance with respect to varying inter-probe spacing for two interconnected conduction channels, which allowsmore » quantitative determination of conductivities from both channels. Using this method, we demonstrate the separation of 2D and 3D conduction in topological insulators by comparing the conductance scaling of Bi 2Se 3, Bi 2Te 2Se, and Sb-doped Bi 2Se 3 with that of a pure 2D conductance of graphene on SiC substrate. We also report the 2D conductance enhancement due to the surface doping effect in topological insulators. This technique can be applied to reveal 2D to 3D crossover of conductance in other complex systems.« less

Some studies on a solid-state sulfur probe for coal gasification systems

NASA Technical Reports Server (NTRS)

Jacob, K. T.; Rao, D. B.; Nelson, H. G.

1978-01-01

As a part of a program for the development of a sulfur probe for monitoring the sulfur potential in coal gasification reactors, an investigation was conducted regarding the efficiency of the solid electrolyte cell Ar+H2+H2S/CaS+CaF2+(Pt)//CaF2//Pt)+CaF2+CaS/H2S+H2+Ar. A demonstration is provided of the theory, design, and operation of a solid-state sulfur probe based on CaF2 electrolyte. It was found that the cell responds to changes in sulfur potential in a manner predicted by the Nernst equation. The response time of the cell at 1225 K, after a small change in temperature or gas composition, was 2.5 Hr, while at a lower temperature of 990 K the response time was approximately 9 hr. The cell emf was insensitive to a moderate increase in the flow rate of the test gas and/or the reference gas. The exact factors affecting the slow response time of galvanic cells based on a CaF2 electrolyte have not yet been determined. The rate-limiting steps may be either the kinetics of electrode reactions or the rate of transport through the electrolyte.

Magnetic-field-induced delocalized to localized transformation in GaAs:N.

PubMed

Alberi, K; Crooker, S A; Fluegel, B; Beaton, D A; Ptak, A J; Mascarenhas, A

2013-04-12

The use of a high magnetic field (57 T) to study the formation and evolution of nitrogen (N) cluster and supercluster states in GaAs:N is demonstrated. A magnetic field is used to lift the conduction band edge and expose resonant N cluster states so that they can be directly experimentally investigated. The reduction of the exciton Bohr radius also results in the fragmentation of N supercluster states, enabling a magnetic field induced delocalized to localized transition. The application of very high magnetic fields thus presents a powerful way to probe percolation phenomena in semiconductors with bound and resonant isoelectronic cluster states.

Quantum phase transitions and local magnetism in Mott insulators: A local probe investigation using muons, neutrons, and photons

NASA Astrophysics Data System (ADS)

Frandsen, Benjamin A.

Mott insulators are materials in which strong correlations among the electrons induce an unconventional insulating state. Rich interplay between the structural, magnetic, and electronic degrees of freedom resulting from the electron correlation can lead to unusual complexity of Mott materials on the atomic scale, such as microscopically heterogeneous phases or local structural correlations that deviate significantly from the average structure. Such behavior must be studied by suitable experimental techniques, i.e. "local probes", that are sensitive to this local behavior rather than just the bulk, average properties. In this thesis, I will present results from our studies of multiple families of Mott insulators using two such local probes: muon spin relaxation (muSR), a probe of local magnetism; and pair distribution function (PDF) analysis of x-ray and neutron total scattering, a probe of local atomic structure. In addition, I will present the development of magnetic pair distribution function analysis, a novel method for studying local magnetic correlations that is highly complementary to the muSR and atomic PDF techniques. We used muSR to study the phase transition from Mott insulator to metal in two archetypal Mott insulating systems: RENiO3 (RE = rare earth element) and V2O3. In both of these systems, the Mott insulating state can be suppressed by tuning a nonthermal parameter, resulting in a "quantum" phase transition at zero temperature from the Mott insulating state to a metallic state. In RENiO3, this occurs through variation of the rare-earth element in the chemical composition; in V 2O3, through the application of hydrostatic pressure. Our results show that the metallic and Mott insulating states unexpectedly coexist in phase-separated regions across a large portion of parameter space near the Mott quantum phase transition and that the magnitude of the ordered antiferromagnetic moment remains constant across the phase diagram until it is abruptly destroyed at the quantum phase transition. Taken together, these findings point unambiguously to a first-order quantum phase transition in these systems. We also conducted x-ray and neutron PDF experiments, which suggest that the distinct atomic structures associated with the insulating and metallic phases similarly coexist near the quantum phase transition. These results have significant implications for our understanding of the Mott metal-insulator quantum phase transition in real materials. The second part of this thesis centers on the derivation and development of the magnetic pair distribution function (mPDF) technique and its application to the antiferromagnetic Mott insulator MnO. The atomic PDF method involves Fourier transforming the x-ray or neutron total scattering intensity from reciprocal space into real space to directly reveal the local atomic correlations in a material, which may deviate significantly from the average crystallographic structure of that material. Likewise, the mPDF method involves Fourier transforming the magnetic neutron total scattering intensity to probe the local correlations of magnetic moments in the material, which may exist on short length scales even when the material has no long-range magnetic order. After deriving the fundamental mPDF equations and providing a proof-of-principle by recovering the known magnetic structure of antiferromagnetic MnO, we used this technique to investigate the short-range magnetic correlations that persist well into the paramagnetic phase of MnO. By combining the mPDF measurements with ab initio calculations of the spin-spin correlation function in paramagnetic MnO, we were able to quantitatively account for the observed mPDF. We also used the mPDF data to evaluate competing ab initio theories, thereby resolving some longstanding questions about the magnetic exchange interactions in MnO.

Single sensor for multiple analytes in different optical channel: Applying for multi-ion response modulation

NASA Astrophysics Data System (ADS)

Liang, Chunshuang; Jiang, Shimei

2017-08-01

A Schiff-base, (2,4-di-tert-butyl-6-((2-hydroxyphenyl-imino)-methyl)phenol) (L), has been improved to function as a simultaneous multi-ion probe in different optical channel. The probe changes from colorless to orangish upon being deprotonated by F-, while the presence of Al3+ significantly enhances the fluorescence of the probe due to the inhibition of Cdbnd N isomerization, cation-induced inhibition of excited-state intramolecular proton transfer (ESIPT), and chelation enhanced fluorescence (CHEF). Dual-channel "off-on" switching behavior resulted from the sequential input of F- and Al3+, reflecting the balance of independent reactions of Al3+ and F- with L and with one another. This sensing phenomenon realizes transformation between multiple states and beautifully mimics a "Write-Read-Erase-Read" logic circuit with two feedback loops.

The robustness of high-Tc superconductivity in underdoped YBa2Cu3O6+x investigated in under strong magnetic fields

NASA Astrophysics Data System (ADS)

Harrison, Neil; Hsu, Y.-T.; Hartstein, M.; Chan, M.; Porras, J.; Loew, T.; Le Tacon, M.; Lonzarich, G.; Keimer, B.; Flux, V.; Sebastian, S.

A central unresolved mystery in high-Tc superconductivity is whether the pairing amplitude is small in the underdoped regime and relates to the superfluid density or whether it is large and relate to the intrinsic energy scales of the Mott insulating parent state. The magnetic field provides a sensitive probe of the pairing amplitude. However, experimental probes of the extent of the vortex state in temperature and magnetic field have thus far been indirect and hence subject to debate. Here we report measurements over a broad range of temperature and magnetic fields which we use to probe the extent of the vortex region in underdoped YBa2Cu3O6+x. and its interplay with quantum oscillations. N.H. acknowledges UU DOE BES Support for ''Science of 100 Tesla''.

Observation of isoscalar and isovector dipole excitations in neutron-rich 20O

NASA Astrophysics Data System (ADS)

Nakatsuka, N.; Baba, H.; Aumann, T.; Avigo, R.; Banerjee, S. R.; Bracco, A.; Caesar, C.; Camera, F.; Ceruti, S.; Chen, S.; Derya, V.; Doornenbal, P.; Giaz, A.; Horvat, A.; Ieki, K.; Inakura, T.; Imai, N.; Kawabata, T.; Kobayashi, N.; Kondo, Y.; Koyama, S.; Kurata-Nishimura, M.; Masuoka, S.; Matsushita, M.; Michimasa, S.; Million, B.; Motobayashi, T.; Murakami, T.; Nakamura, T.; Ohnishi, T.; Ong, H. J.; Ota, S.; Otsu, H.; Ozaki, T.; Saito, A.; Sakurai, H.; Scheit, H.; Schindler, F.; Schrock, P.; Shiga, Y.; Shikata, M.; Shimoura, S.; Steppenbeck, D.; Sumikama, T.; Syndikus, I.; Takeda, H.; Takeuchi, S.; Tamii, A.; Taniuchi, R.; Togano, Y.; Tscheuschner, J.; Tsubota, J.; Wang, H.; Wieland, O.; Wimmer, K.; Yamaguchi, Y.; Yoneda, K.; Zenihiro, J.

2017-05-01

The isospin characters of low-energy dipole excitations in neutron-rich unstable nucleus 20O were investigated, for the first time in unstable nuclei. Two spectra obtained from a dominant isovector probe (20O + Au) and a dominant isoscalar probe (20O + α) were compared and analyzed by the distorted-wave Born approximation to extract independently the isovector and isoscalar dipole strengths. Two known 1- states with large isovector dipole strengths at energies of 5.36(5) MeV (11-) and 6.84(7) MeV (12-) were also excited by the isoscalar probe. These two states were found to have different isoscalar dipole strengths, 2.70(32)% (11-) and 0.67(12)% (12-), respectively, in exhaustion of the isoscalar dipole-energy-weighted sum rule. The difference in isoscalar strength indicated that they have different underlying structures.

Magnetic actuation of hair cells

NASA Astrophysics Data System (ADS)

Rowland, David; Roongthumskul, Yuttana; Lee, Jae-Hyun; Cheon, Jinwoo; Bozovic, Dolores

2011-11-01

The bullfrog sacculus contains mechanically sensitive hair cells whose stereociliary bundles oscillate spontaneously when decoupled from the overlying membrane. Steady-state offsets on the resting position of a hair bundle can suppress or modulate this native motility. To probe the dynamics of spontaneous oscillation in the proximity of the critical point, we describe here a method for mechanical actuation that avoids loading the bundles or contributing to the viscous drag. Magnetite beads were attached to the tips of the stereocilia, and a magnetic probe was used to impose deflections. This technique allowed us to observe the transition from multi-mode to single-mode state in freely oscillating bundles, as well as the crossover from the oscillatory to the quiescent state.

Probing the Single-Particle Character of Rotational States in F 19 Using a Short-Lived Isomeric Beam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Santiago-Gonzalez, D.; Auranen, K.; Avila, M. L.

2018-03-01

A beam containing a substantial component of both the J(pi) = 5(+), T-1/2 = 162 ns isomeric state of F-18 and its 1(+), 109.77-min ground state is utilized to study members of the ground-state rotational band in F-19 through the neutron transfer reaction (d,p) in inverse kinematics. The resulting spectroscopic strengths confirm the single-particle nature of the 13/2(+) band-terminating state. The agreement between shell-model calculations using an interaction constructed within the sd shell, and our experimental results reinforces the idea of a single-particle-collective duality in the descriptions of the structure of atomic nuclei.

Comparison of Cherenkov excited fluorescence and phosphorescence molecular sensing from tissue with external beam irradiation.

PubMed

Lin, Huiyun; Zhang, Rongxiao; Gunn, Jason R; Esipova, Tatiana V; Vinogradov, Sergei; Gladstone, David J; Jarvis, Lesley A; Pogue, Brian W

2016-05-21

Ionizing radiation delivered by a medical linear accelerator (LINAC) generates Cherenkov emission within the treated tissue. A fraction of this light, in the 600-900 nm wavelength region, propagates through centimeters of tissue and can be used to excite optical probes in vivo, enabling molecular sensing of tissue analytes. The success of isolating the emission signal from this Cherenkov excitation background is dependent on key factors such as: (i) the Stokes shift of the probe spectra; (ii) the excited state lifetime; (iii) the probe concentration; (iv) the depth below the tissue surface; and (v) the radiation dose used. Previous studies have exclusively focused on imaging phosphorescent dyes, rather than fluorescent dyes. However there are only a few biologically important phosphorescent dyes and yet in comparison there are thousands of biologically relevant fluorescent dyes. So in this study the focus was a study of efficacy of Cherenkov-excited luminescence using fluorescent commercial near-infrared probes, IRDye 680RD, IRDye 700DX, and IRDye 800CW, and comparing them to the well characterized phosphorescent probe Oxyphor PtG4, an oxygen sensitive dye. Each probe was excited by Cherenkov light from a 6 MV external radiation beam, and measured in continuous wave or time-gated modes. The detection was performed by spectrally resolving the luminescence signals, and measuring them with spectrometer-based separation on an ICCD detector. The results demonstrate that IRDye 700DX and PtG4 allowed for the maximal signal to noise ratio. In the case of the phosphorescent probe, PtG4, with emission decays on the microsecond (μs) time scale, time-gated acquisition was possible, and it allowed for higher efficacy in terms of the probe concentration and detection depth. Phantoms containing the probe at 5 mm depth could be detected at concentrations down to the nanoMolar range, and at depths into the tissue simulating phantom near 3 cm. In vivo studies showed that 5 nmol of dye was readily detected with radiation doses less than 5 cGy. Since concentration, radiation dose and depth each contribute to the level of the detected signal, it may be possible to improve any of these parameters at expense of the others. This paradigm of nanoMolar sensitivity for optical reporters in vivo introduces the concept of molecular sensing of tumors during therapy or diagnostically with biologically relevant concentrations of fluorescent reporters.

Comparison of Cherenkov excited fluorescence and phosphorescence molecular sensing from tissue with external beam irradiation

NASA Astrophysics Data System (ADS)

Lin, Huiyun; Zhang, Rongxiao; Gunn, Jason R.; Esipova, Tatiana V.; Vinogradov, Sergei; Gladstone, David J.; Jarvis, Lesley A.; Pogue, Brian W.

2016-05-01

Ionizing radiation delivered by a medical linear accelerator (LINAC) generates Cherenkov emission within the treated tissue. A fraction of this light, in the 600-900 nm wavelength region, propagates through centimeters of tissue and can be used to excite optical probes in vivo, enabling molecular sensing of tissue analytes. The success of isolating the emission signal from this Cherenkov excitation background is dependent on key factors such as: (i) the Stokes shift of the probe spectra; (ii) the excited state lifetime; (iii) the probe concentration; (iv) the depth below the tissue surface; and (v) the radiation dose used. Previous studies have exclusively focused on imaging phosphorescent dyes, rather than fluorescent dyes. However there are only a few biologically important phosphorescent dyes and yet in comparison there are thousands of biologically relevant fluorescent dyes. So in this study the focus was a study of efficacy of Cherenkov-excited luminescence using fluorescent commercial near-infrared probes, IRDye 680RD, IRDye 700DX, and IRDye 800CW, and comparing them to the well characterized phosphorescent probe Oxyphor PtG4, an oxygen sensitive dye. Each probe was excited by Cherenkov light from a 6 MV external radiation beam, and measured in continuous wave or time-gated modes. The detection was performed by spectrally resolving the luminescence signals, and measuring them with spectrometer-based separation on an ICCD detector. The results demonstrate that IRDye 700DX and PtG4 allowed for the maximal signal to noise ratio. In the case of the phosphorescent probe, PtG4, with emission decays on the microsecond (μs) time scale, time-gated acquisition was possible, and it allowed for higher efficacy in terms of the probe concentration and detection depth. Phantoms containing the probe at 5 mm depth could be detected at concentrations down to the nanoMolar range, and at depths into the tissue simulating phantom near 3 cm. In vivo studies showed that 5 nmol of dye was readily detected with radiation doses less than 5 cGy. Since concentration, radiation dose and depth each contribute to the level of the detected signal, it may be possible to improve any of these parameters at expense of the others. This paradigm of nanoMolar sensitivity for optical reporters in vivo introduces the concept of molecular sensing of tumors during therapy or diagnostically with biologically relevant concentrations of fluorescent reporters.

Formative Assessment Probes: When Is the Next Full Moon? Using K-2 Concept Cartoons

ERIC Educational Resources Information Center

Keeley, Page

2013-01-01

This column focuses on promoting learning through assessment. This month's issue uses concept cartoons to assess students' ideas about the moon. Concept cartoons, formative assessment tools that reveal students' preconceptions and probe for conceptual understanding, have recently become popular in the United States, with teachers…

OCR Pace on Probes Quickens

ERIC Educational Resources Information Center

Maxwell, Lesli A.

2011-01-01

In the 21 months since U.S. Secretary of Education Arne Duncan stood on an iconic bridge in Selma, Alabama, and pledged to aggressively combat discrimination in the nation's schools, federal education officials have launched dozens of new probes in school districts and states that reach into civil rights issues that previously received little, if…

History, rare, and multiple events of mechanical unfolding of repeat proteins

NASA Astrophysics Data System (ADS)

Sumbul, Fidan; Marchesi, Arin; Rico, Felix

2018-03-01

Mechanical unfolding of proteins consisting of repeat domains is an excellent tool to obtain large statistics. Force spectroscopy experiments using atomic force microscopy on proteins presenting multiple domains have revealed that unfolding forces depend on the number of folded domains (history) and have reported intermediate states and rare events. However, the common use of unspecific attachment approaches to pull the protein of interest holds important limitations to study unfolding history and may lead to discarding rare and multiple probing events due to the presence of unspecific adhesion and uncertainty on the pulling site. Site-specific methods that have recently emerged minimize this uncertainty and would be excellent tools to probe unfolding history and rare events. However, detailed characterization of these approaches is required to identify their advantages and limitations. Here, we characterize a site-specific binding approach based on the ultrastable complex dockerin/cohesin III revealing its advantages and limitations to assess the unfolding history and to investigate rare and multiple events during the unfolding of repeated domains. We show that this approach is more robust, reproducible, and provides larger statistics than conventional unspecific methods. We show that the method is optimal to reveal the history of unfolding from the very first domain and to detect rare events, while being more limited to assess intermediate states. Finally, we quantify the forces required to unfold two molecules pulled in parallel, difficult when using unspecific approaches. The proposed method represents a step forward toward more reproducible measurements to probe protein unfolding history and opens the door to systematic probing of rare and multiple molecule unfolding mechanisms.

7th International Workshop on Microbeam Probes of Cellular Radiation Response

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brenner, David J.

2009-07-21

The extended abstracts that follow present a summary of the Proceedings of the 7th International Workshop: Microbeam Probes of Cellular Radiation Response, held at Columbia University’s Kellogg Center in New York City on March 15–17, 2006. These International Workshops on Microbeam Probes of Cellular Radiation Response have been held regularly since 1993 (1–5). Since the first workshop, there has been a rapid growth (see Fig. 1) in the number of centers developing microbeams for radiobiological research, and worldwide there are currently about 30 microbeams in operation or under development. Single-cell/single-particle microbeam systems can deliver beams of different ionizing radiations withmore » a spatial resolution of a few micrometers down to a few tenths of a micrometer. Microbeams can be used to addressquestions relating to the effects of low doses of radiation (a single radiation track traversing a cell or group of cells), to probe subcellular targets (e.g. nucleus or cytoplasm), and to address questions regarding the propagation of information about DNA damage (for example, the radiation-induced bystander effect). Much of the recent research using microbeams has been to study low-dose effects and ‘‘non-targeted’’ responses such as bystander effects, genomic instability and adaptive responses. This Workshop provided a forum to assess the current state of microbeam technology and current biological applications and to discuss future directions for development, both technological and biological. Over 100 participants reviewed the current state of microbeam research worldwide and reported on new technological developments in the fields of both physics and biology.« less

Optimal stimulus scheduling for active estimation of evoked brain networks.

PubMed

Kafashan, MohammadMehdi; Ching, ShiNung

2015-12-01

We consider the problem of optimal probing to learn connections in an evoked dynamic network. Such a network, in which each edge measures an input-output relationship between sites in sensor/actuator-space, is relevant to emerging applications in neural mapping and neural connectivity estimation. We show that the problem of scheduling nodes to a probe (i.e., stimulate) amounts to a problem of optimal sensor scheduling. By formulating the evoked network in state-space, we show that the solution to the greedy probing strategy has a convenient form and, under certain conditions, is optimal over a finite horizon. We adopt an expectation maximization technique to update the state-space parameters in an online fashion and demonstrate the efficacy of the overall approach in a series of detailed numerical examples. The proposed method provides a principled means to actively probe time-varying connections in neuronal networks. The overall method can be implemented in real time and is particularly well-suited to applications in stimulation-based cortical mapping in which the underlying network dynamics are changing over time.

Optimal stimulus scheduling for active estimation of evoked brain networks

NASA Astrophysics Data System (ADS)

Kafashan, MohammadMehdi; Ching, ShiNung

2015-12-01

Objective. We consider the problem of optimal probing to learn connections in an evoked dynamic network. Such a network, in which each edge measures an input-output relationship between sites in sensor/actuator-space, is relevant to emerging applications in neural mapping and neural connectivity estimation. Approach. We show that the problem of scheduling nodes to a probe (i.e., stimulate) amounts to a problem of optimal sensor scheduling. Main results. By formulating the evoked network in state-space, we show that the solution to the greedy probing strategy has a convenient form and, under certain conditions, is optimal over a finite horizon. We adopt an expectation maximization technique to update the state-space parameters in an online fashion and demonstrate the efficacy of the overall approach in a series of detailed numerical examples. Significance. The proposed method provides a principled means to actively probe time-varying connections in neuronal networks. The overall method can be implemented in real time and is particularly well-suited to applications in stimulation-based cortical mapping in which the underlying network dynamics are changing over time.

Near infrared fluorescence-based bacteriophage particles for ratiometric pH imaging.

PubMed

Hilderbrand, Scott A; Kelly, Kimberly A; Niedre, Mark; Weissleder, Ralph

2008-08-01

Fluorogenic imaging agents emitting in the near-infrared are becoming important research tools for disease investigation in vivo. Often pathophysiological states such as cancer and cystic fibrosis are associated with disruptions in acid/base homeostasis. The development of optical sensors for pH imaging would facilitate the investigation of these diseased conditions. In this report, the design and synthesis of a ratiometric near-infrared emitting probe for pH quantification is detailed. The pH-responsive probe is prepared by covalent attachment of pH-sensitive and pH-insensitive fluorophores to a bacteriophage particle scaffold. The pH-responsive cyanine dye, HCyC-646, used to construct the probe, has a fluorogenic pKa of 6.2, which is optimized for visualization of acidic pH often associated with tumor hypoxia and other diseased states. Incorporation of pH-insensitive reference dyes enables the ratiometric determination of pH independent of the probe concentration. With the pH-responsive construct, measurement of intracellular pH and accurate determination of pH through optically diffuse biological tissue is demonstrated.

Asian American Immigrant Parents Supporting Children with Autism: Perceptions of Fathers and Mothers

ERIC Educational Resources Information Center

Wang, Hui-Ting; West, Elizabeth A.

2016-01-01

Asian American immigrant parents supporting children with autism spectrum disorders (ASD) has been understudied. The purpose of this qualitative study was to probe the perceptions of Mandarin-speaking immigrant mothers and fathers raising children with ASD in the United States. Ten participating parents were first-generation native…

Automated cockpits special report, part 2.

PubMed

1995-02-06

Part two of this report includes the following articles: Studies Highlight Automation 'Surprises'; Pilots Union Presses for Improved Displays; United Training Stresses Cockpit Discipline; Former NASA Ames Experts Hold Key Airline Posts; Aiding Mode Awareness; Military Cockpits Keep Autopilot Interface Simple; Gulfstream Using Vertical Profile Display; and, Data Recorders Crucial to State-of-art Crash Probes.

A Degree Is Not Enough: A Quantitative Study of Aspects of Pre-Service Science Teachers' Chemistry Content Knowledge

ERIC Educational Resources Information Center

Kind, Vanessa

2014-01-01

Aspects of chemistry content knowledge held by 265 UK-based pre-service teachers (PSTs) were probed using 28 diagnostic questions in five chemistry concept areas, "Particle theory and changes of state", "Mass conservation" (taught to 11-14-year-olds), and "Chemical bonding", "Mole calculations" and…

Potential transmission of Pantoea spp. and Serratia marcescens (Enterobacteriales: Enterobacteriaceae) to plants by Lygus hesperus (Hemiptera: Miridae)

USDA-ARS?s Scientific Manuscript database

Lygus hesperus Knight (Hemiptera: Miridae) is a key agricultural pest in the western United States. In a recent study, proteins from Pantoea ananatis and Serratia marcescens (Enterobacteriales: Enterobacteriaceae) were identified in diet that was stylet-probed and fed upon by L. hesperus adults. P...

Application of Algebra Curriculum-Based Measurements for Decision Making in Middle and High School

ERIC Educational Resources Information Center

Johnson, Evelyn S.; Galow, Patricia A.; Allenger, Robert

2013-01-01

This article reports the results of a study examining the utility of curriculum-based measurement (CBM) in algebra for predicting performance on a state math assessment and informing instructional placement decisions for students in seventh, eighth, and tenth grades. Students completed six Basic Skills algebra probes across different time…

A Comparison of Simultaneous Prompting and Constant Time Delay Procedures in Teaching State Capitals

ERIC Educational Resources Information Center

Head, Kenneth David; Collins, Belva C.; Schuster, John W.; Ault, Melinda Jones

2011-01-01

This investigation compared the effectiveness and efficiency of constant time delay (CTD) and simultaneous prompting (SP) procedures in teaching discrete social studies facts to 4 high school students with learning and behavior disorders using an adapted alternating treatments design nested within a multiple probe design. The results indicated…

The 68mCu/68Cu isotope as a new probe for hyperfine studies: The nuclear moments

NASA Astrophysics Data System (ADS)

Fenta, A. S.; Pallada, S.; Correia, J. G.; Stachura, M.; Johnston, K.; Gottberg, A.; Mokhles Gerami, A.; Röder, J.; Grawe, H.; Brown, B. A.; Köster, U.; Mendonça, T. M.; Ramos, J. P.; Marsh, B. A.; Day Goodacre, T.; Amaral, V. S.; Pereira, L. M. C.; Borge, M. J. G.; Haas, H.

2016-09-01

Time Differential Perturbed Angular Correlation of γ-rays (TDPAC) experiments were performed for the first time in the decay of 68m Cu (6-, 721 \\text{keV}, 3.75 \\text{min}) produced at the ISOLDE facility at CERN. Due to the short half-life of the source isotope, the measurements were carried out online. The intermediate state (2+, 84.1 \\text{keV}, 7.84 \\text{ns}) offers the unique opportunity to study the electromagnetic fields acting at a copper probe in condensed matter via hyperfine interactions. The present work allowed determination of the nuclear moments for this state. The electric quadrupole moment |Q(2+,84.1 \\text{keV})|=0.110(3) \\text{b} was obtained from an experiment performed in Cu2O and the magnetic dipole moment |μ|=2.857(6) μ_\\text{N} from measurements in cobalt and nickel foils. The results are discussed in the framework of shell model calculations and the additivity rule for nuclear moments with respect to the robustness of the N = 40 sub-shell.

Large Observatory for x-ray Timing (LOFT-P): a Probe-class mission concept study

NASA Astrophysics Data System (ADS)

Wilson-Hodge, Colleen A.; Ray, Paul S.; Chakrabarty, Deepto; Feroci, Marco; Alvarez, Laura; Baysinger, Michael; Becker, Chris; Bozzo, Enrico; Brandt, Soren; Carson, Billy; Chapman, Jack; Dominguez, Alexandra; Fabisinski, Leo; Gangl, Bert; Garcia, Jay; Griffith, Christopher; Hernanz, Margarita; Hickman, Robert; Hopkins, Randall; Hui, Michelle; Ingram, Luster; Jenke, Peter; Korpela, Seppo; Maccarone, Tom; Michalska, Malgorzata; Pohl, Martin; Santangelo, Andrea; Schanne, Stephane; Schnell, Andrew; Stella, Luigi; van der Klis, Michiel; Watts, Anna; Winter, Berend; Zane, Silvia

2016-07-01

LOFT-P is a mission concept for a NASA Astrophysics Probe-Class (<$1B) X-ray timing mission, based on the LOFT M-class concept originally proposed to ESAs M3 and M4 calls. LOFT-P requires very large collecting area, high time resolution, good spectral resolution, broad-band spectral coverage (2-30 keV), highly flexible scheduling, and an ability to detect and respond promptly to time-critical targets of opportunity. It addresses science questions such as: What is the equation of state of ultra dense matter? What are the effects of strong gravity on matter spiraling into black holes? It would be optimized for sub-millisecond timing of bright Galactic X-ray sources including X-ray bursters, black hole binaries, and magnetars to study phenomena at the natural timescales of neutron star surfaces and black hole event horizons and to measure mass and spin of black holes. These measurements are synergistic to imaging and high-resolution spectroscopy instruments, addressing much smaller distance scales than are possible without very long baseline X-ray interferometry, and using complementary techniques to address the geometry and dynamics of emission regions. LOFT-P would have an effective area of >6 m2, > 10x that of the highly successful Rossi X-ray Timing Explorer (RXTE). A sky monitor (2-50 keV) acts as a trigger for pointed observations, providing high duty cycle, high time resolution monitoring of the X-ray sky with 20 times the sensitivity of the RXTE All-Sky Monitor, enabling multi-wavelength and multimessenger studies. A probe-class mission concept would employ lightweight collimator technology and large-area solid-state detectors, segmented into pixels or strips, technologies which have been recently greatly advanced during the ESA M3 Phase A study of LOFT. Given the large community interested in LOFT (>800 supporters*, the scientific productivity of this mission is expected to be very high, similar to or greater than RXTE ( 2000 refereed publications). We describe the results of a study, recently completed by the MSFC Advanced Concepts Office, that demonstrates that such a mission is feasible within a NASA probe-class mission budget.

State of the art review: Intravaginal probes for recording electromyography from the pelvic floor muscles.

PubMed

Keshwani, Nadia; McLean, Linda

2015-02-01

To survey commercially available intravaginal probes designed to record electromyography (EMG) from the pelvic floor muscles (PFMs), and to discuss the strengths and limitations of current technology. The MEDLINE EMBASE, CINAHL, PEDRO, and Cochrane databases were searched for articles in which intravaginal probes were described as having been used to record EMG from the PFMs. The World Wide Web was also searched using the Google search engine to find devices used to record EMG from the PFMs. Finally, a Canadian distributer of intravaginal probes was contacted to identify intravaginal EMG probes not identified through other methods. The specifications of each probe were determined through the manufacturer or their website, and each device was acquired by the investigators to verify the specifications and electrode configuration. The devices were evaluated against international standards for recording EMG data. Sixteen different models of commercially available intravaginal probes were identified: seven from published research papers, seven using the World Wide Web, and two through communication with a distributer. The probes vary in shape, dimensions, electrode positioning, and electrode configuration, with many designs prone to recording motion artifact, crosstalk, and/or inappropriate EMG signals. All commercially available intravaginal probes had deficiencies in their design such as problems with probe geometry, electrode size, location, and/or configuration. Improved intravaginal EMG probes should be developed for use in research and clinical practice. © 2013 Wiley Periodicals, Inc.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nenov, Artur, E-mail: Artur.Nenov@unibo.it; Giussani, Angelo; Segarra-Martí, Javier

Pump-probe electronic spectroscopy using femtosecond laser pulses has evolved into a standard tool for tracking ultrafast excited state dynamics. Its two-dimensional (2D) counterpart is becoming an increasingly available and promising technique for resolving many of the limitations of pump-probe caused by spectral congestion. The ability to simulate pump-probe and 2D spectra from ab initio computations would allow one to link mechanistic observables like molecular motions and the making/breaking of chemical bonds to experimental observables like excited state lifetimes and quantum yields. From a theoretical standpoint, the characterization of the electronic transitions in the visible (Vis)/ultraviolet (UV), which are excited viamore » the interaction of a molecular system with the incoming pump/probe pulses, translates into the determination of a computationally challenging number of excited states (going over 100) even for small/medium sized systems. A protocol is therefore required to evaluate the fluctuations of spectral properties like transition energies and dipole moments as a function of the computational parameters and to estimate the effect of these fluctuations on the transient spectral appearance. In the present contribution such a protocol is presented within the framework of complete and restricted active space self-consistent field theory and its second-order perturbation theory extensions. The electronic excited states of adenine have been carefully characterized through a previously presented computational recipe [Nenov et al., Comput. Theor. Chem. 1040–1041, 295-303 (2014)]. A wise reduction of the level of theory has then been performed in order to obtain a computationally less demanding approach that is still able to reproduce the characteristic features of the reference data. Foreseeing the potentiality of 2D electronic spectroscopy to track polynucleotide ground and excited state dynamics, and in particular its expected ability to provide conformational dependent fingerprints in dimeric systems, the performances of the selected reduced level of calculations have been tested in the construction of 2D electronic spectra for the in vacuo adenine monomer and the unstacked adenine homodimer, thereby exciting the L{sub b}/L{sub a} transitions with the pump pulse pair and probing in the Vis to near ultraviolet spectral window.« less

Investigation of excited 0+ states in 160Er populated via the (p, t) two-neutron transfer reaction

NASA Astrophysics Data System (ADS)

Burbadge, C.; Garrett, P. E.; Ball, G. C.; Bildstein, V.; Diaz Varela, A.; Dunlop, M. R.; Dunlop, R.; Faesternann, T.; Hertenberger, R.; Jamieson, D. S.; Kisliuk, D.; Leach, K. G.; Loranger, J.; MacLean, A. D.; Radich, A. J.; Rand, E. T.; Svensson, C. E.; Triambak, S.; Wirth, H.-F.

2018-05-01

Many efforts have been made in nuclear structure physics to interpret the nature of low-lying excited 0+ states in well-deformed rare-earth nuclei. However, one of the difficulties in resolving the nature of these states is that there is a paucity of data. In this work, excited 0+ states in the N = 92 nucleus 160Er were studied via the 162Er(p, t)160Er two-neutron transfer reaction, which is ideal for probing 0+ → 0+ transitions, at the Maier-Leibnitz-Laboratorium in Garching, Germany. Reaction products were momentum-analyzed with a Quadrupole-3-Dipole magnetic spectrograph. The 0+2 state was observed to be strongly populated with 18% of the ground state strength.

Attosecond Spectroscopy Probing Electron Correlation Dynamics

NASA Astrophysics Data System (ADS)

Winney, Alexander H.

Electrons are the driving force behind every chemical reaction. The exchange, ionization, or even relaxation of electrons is behind every bond broken or formed. According to the Bohr model of the atom, it takes an electron 150 as to orbit a proton[6]. With this as a unit time scale for an electron, it is clear that a pulse duration of several femtoseconds will not be sufficient to understanding electron dynamics. Our work demonstrates both technical and scientific achievements that push the boundaries of attosecond dynamics. TDSE studies show that amplification the yield of high harmonic generation (HHG) may be possible with transverse confinement of the electron. XUV-pump-XUV-probe shows that the yield of APT train can be sufficient for 2-photon double ionization studies. A zero dead-time detection system allows for the measurement of state-resolved double ionization for the first time. Exploiting attosecond angular streaking[7] probes sequential and non-sequential double ionization via electron-electron correlations with attosecond time resolution. Finally, using recoil frame momentum correlation, the fast dissociation of CH 3I reveals important orbital ionization dynamics of non-dissociative & dissociative, single & double ionization.

Probing the interaction between nanoparticles and lipid membranes by quartz crystal microbalance with dissipation monitoring

NASA Astrophysics Data System (ADS)

Yousefi, Nariman; Tufenkji, Nathalie

2016-12-01

There is increasing interest in using quartz crystal microbalance with dissipation monitoring (QCM-D) to investigate the interaction of nanoparticles (NPs) with model surfaces. The high sensitivity, ease of use and the ability to monitor interactions in real-time has made it a popular technique for colloid chemists, biologists, bioengineers and biophysicists. QCM-D has been recently used to probe the interaction of NPs with supported lipid bilayers (SLBs) as model cell membranes. The interaction of NPs with SLBs is highly influenced by the quality of the lipid bilayers. Unlike many surface sensitive techniques, using QCM-D, the quality of SLBs can be assessed in real-time, hence QCM-D studies on SLB-NP interactions are less prone to the artefacts arising from bilayers that are not well formed. The ease of use and commercial availability of a wide range of sensor surfaces also have made QCM-D a versatile tool for studying NP interactions with lipid bilayers. In this review, we summarize the state-of-the-art on QCM-D based techniques for probing the interactions of NPs with lipid bilayers.

Visualizing Chemical Bonds in Synthetic Molecules

NASA Astrophysics Data System (ADS)

Collins, Laura C.; Ruth, Anthony; Green, David B.; Janko, Boldizsar; Gomes, Kenjiro K.

The use of synthetic quantum systems makes it possible to study phenomena that cannot be probed by conventional experiments. We created synthetic molecules using atomic manipulation and directly imaged the chemical bonds using tunneling spectroscopy. These synthetic systems allow us to probe the structure and electronic properties of chemical bonds in molecules, including those that would be unstable in nature, with unprecedented detail. The experimental images of electronic states in our synthetic molecules show a remarkable match to the charge distribution predicted by density functional theory calculations. The statistical analysis of the spectroscopy of these molecules can be adapted in the future to quantify aromaticity, which has been difficult to quantify universally thus far due to vague definitions. We can also study anti-aromatic molecules which are unstable naturally, to illuminate the electronic consequences of antiaromaticity.

Polarization spectroscopy of the sodium dimer utilizing a triple-resonance technique in the presence of argon

NASA Astrophysics Data System (ADS)

Arndt, Phillip; Horton, Timothy; McFarland, Jacob; Bayram, Burcin; Miami University Spectroscopy Team

2015-05-01

The collisional dynamics of molecular sodium in the 61Σg electronic state is under investigation using a triple resonance technique in the presence of argon. A continuous wave ring dye laser is used to populate specific rovibrational levels of the A1Σu electronic state. A pump-probe technique is then employed where the pump laser populates the 61Σg state, and the probe laser dumps the population to the B1Σu state. From this level, fluorescence is detected as the system decays to the X1Σg state. We measure the polarization of this signal in the presence of various argon pressures. We will present our current work as well as the processes involved in the experiment. Financial support from the National Science Foundation (Grant No. NSF-PHY-1309571) is gratefully acknowledged.

Probing lithium-ion batteries' state-of-charge using ultrasonic transmission - Concept and laboratory testing

NASA Astrophysics Data System (ADS)

Gold, Lukas; Bach, Tobias; Virsik, Wolfgang; Schmitt, Angelika; Müller, Jana; Staab, Torsten E. M.; Sextl, Gerhard

2017-03-01

For electrically powered applications such as consumer electronics and especially for electric vehicles a precise state-of-charge estimation for their lithium-ion batteries is desired to reduce aging, e.g. avoiding detrimental states-of-charge. Today, this estimation is performed by battery management systems that solely rely on charge bookkeeping and cell voltage measurements. In the present work we introduce a new, physical probe for the state-of-charge based on ultrasonic transmission. Within the simple experimental setup raised cosine pulses are applied to lithium-ion battery pouch cells, whose signals are sensitive to changes in porosity of the graphite anode during charging/dis-charging and, therefore, to the state-of-charge. The underlying physical principle can be related to Biot's theory about propagation of waves in fluid saturated porous media and by including scattering by boundary layers inside the cell.

Preparation, Characterization and Application of Optical Switch Probes.

PubMed

Petchprayoon, Chutima; Marriott, Gerard

2010-08-01

Optical switches represent a new class of molecular probe with applications in high contrast imaging and optical manipulation of protein interactions. Small molecule, organic optical switches based on nitrospirobenzopyran (NitroBIPS) and their reactive derivatives and conjugates undergo efficient, rapid and reversible, orthogonal optically-driven transitions between a colorless spiro (SP) state and a colored merocyanine (MC) state. The excited MC-state also emits fluorescence, which serves as readout of the state of the switch. Defined optical perturbations of SP and MC generate a defined waveform of MC-fluorescence that can be isolated against unmodulated background signals by using a digital optical lock-in detection approach or to control specific dipolar interactions on proteins. The protocols describe general procedures for the synthesis and spectroscopic characterization of NitroBIPS and specifically labeled conjugates along with methods for the manipulation of dipolar interactions on proteins and imaging of the MC-state of NitroBIPS within living cells.

Target-cancer-cell-specific activatable fluorescence imaging probes: rational design and in vivo applications.

PubMed

Kobayashi, Hisataka; Choyke, Peter L

2011-02-15

Conventional imaging methods, such as angiography, computed tomography (CT), magnetic resonance imaging (MRI), and radionuclide imaging, rely on contrast agents (iodine, gadolinium, and radioisotopes, for example) that are "always on." Although these indicators have proven clinically useful, their sensitivity is lacking because of inadequate target-to-background signal ratio. A unique aspect of optical imaging is that fluorescence probes can be designed to be activatable, that is, only "turned on" under certain conditions. These probes are engineered to emit signal only after binding a target tissue; this design greatly increases sensitivity and specificity in the detection of disease. Current research focuses on two basic types of activatable fluorescence probes. The first developed were conventional enzymatically activatable probes. These fluorescent molecules exist in the quenched state until activated by enzymatic cleavage, which occurs mostly outside of the cells. However, more recently, researchers have begun designing target-cell-specific activatable probes. These fluorophores exist in the quenched state until activated within targeted cells by endolysosomal processing, which results when the probe binds specific receptors on the cell surface and is subsequently internalized. In this Account, we present a review of the rational design and in vivo applications of target-cell-specific activatable probes. In engineering these probes, researchers have asserted control over a variety of factors, including photochemistry, pharmacological profile, and biological properties. Their progress has recently allowed the rational design and synthesis of target-cell-specific activatable fluorescence imaging probes, which can be conjugated to a wide variety of targeting molecules. Several different photochemical mechanisms have been utilized, each of which offers a unique capability for probe design. These include self-quenching, homo- and hetero-fluorescence resonance energy transfer (FRET), H-dimer formation, and photon-induced electron transfer (PeT). In addition, the repertoire is further expanded by the option for reversibility or irreversibility of the signal emitted through these mechanisms. Given the wide range of photochemical mechanisms and properties, target-cell-specific activatable probes have considerable flexibility and can be adapted to specific diagnostic needs. A multitude of cell surface molecules, such as overexpressed growth factor receptors, are directly related to carcinogenesis and thus provide numerous targets highly specific for cancer. This discussion of the chemical, pharmacological, and biological basis of target-cell-specific activatable imaging probes, and methods for successfully designing them, underscores the systematic, rational basis for further developing in vivo cancer imaging.

Polyethylene glycol versus dual sugar assay for gastrointestinal permeability analysis: is it time to choose?

PubMed Central

van Wijck, Kim; Bessems, Babs AFM; van Eijk, Hans MH; Buurman, Wim A; Dejong, Cornelis HC; Lenaerts, Kaatje

2012-01-01

Background Increased intestinal permeability is an important measure of disease activity and prognosis. Currently, many permeability tests are available and no consensus has been reached as to which test is most suitable. The aim of this study was to compare urinary probe excretion and accuracy of a polyethylene glycol (PEG) assay and dual sugar assay in a double-blinded crossover study to evaluate probe excretion and the accuracy of both tests. Methods Gastrointestinal permeability was measured in nine volunteers using PEG 400, PEG 1500, and PEG 3350 or lactulose-rhamnose. On 4 separate days, permeability was analyzed after oral intake of placebo or indomethacin, a drug known to increase intestinal permeability. Plasma intestinal fatty acid binding protein and calprotectin levels were determined to verify compromised intestinal integrity after indomethacin consumption. Urinary samples were collected at baseline, hourly up to 5 hours after probe intake, and between 5 and 24 hours. Urinary excretion of PEG and sugars was determined using high-pressure liquid chromatography-evaporative light scattering detection and liquid chromatography-mass spectrometry, respectively. Results Intake of indomethacin increased plasma intestinal fatty acid-binding protein and calprotectin levels, reflecting loss of intestinal integrity and inflammation. In this state of indomethacin-induced gastrointestinal compromise, urinary excretion of the three PEG probes and lactulose increased compared with placebo. Urinary PEG 400 excretion, the PEG 3350/PEG 400 ratio, and the lactulose/rhamnose ratio could accurately detect indomethacin-induced increases in gastrointestinal permeability, especially within 2 hours of probe intake. Conclusion Hourly urinary excretion and diagnostic accuracy of PEG and sugar probes show high concordance for detection of indomethacin-induced increases in gastrointestinal permeability. This comparative study improves our knowledge of permeability analysis in man by providing a clear overview of both tests and demonstrates equivalent performance in the current setting. PMID:22888267

Impedance-controlled ultrasound probe

NASA Astrophysics Data System (ADS)

Gilbertson, Matthew W.; Anthony, Brian W.

2011-03-01

An actuated hand-held impedance-controlled ultrasound probe has been developed. The controller maintains a prescribed contact state (force and velocity) between the probe and a patient's body. The device will enhance the diagnostic capability of free-hand elastography and swept-force compound imaging, and also make it easier for a technician to acquire repeatable (i.e. directly comparable) images over time. The mechanical system consists of an ultrasound probe, ball-screw-driven linear actuator, and a force/torque sensor. The feedback controller commands the motor to rotate the ball-screw to translate the ultrasound probe in order to maintain a desired contact force. It was found that users of the device, with the control system engaged, maintain a constant contact force with 15 times less variation than without the controller engaged. The system was used to determine the elastic properties of soft tissue.

Solid-state nanopores of controlled geometry fabricated in a transmission electron microscope

NASA Astrophysics Data System (ADS)

Qian, Hui; Egerton, Ray F.

2017-11-01

Energy-filtered transmission electron microscopy and electron tomography were applied to in situ studies of the formation, shape, and diameter of nanopores formed in a silicon nitride membrane in a transmission electron microscope. The nanopore geometry was observed in three dimensions by electron tomography. Drilling conditions, such as probe current, beam convergence angle, and probe position, affect the formation rate and the geometry of the pores. With a beam convergence semi-angle of α = 22 mrad, a conical shaped nanopore is formed but at α = 45 mrad, double-cone (hourglass-shaped) nanopores were produced. Nanopores with an effective diameter between 10 nm and 1.8 nm were fabricated by controlling the drilling time.

Amplitude mode oscillations in pump-probe photoemission spectra from a d -wave superconductor

NASA Astrophysics Data System (ADS)

Nosarzewski, B.; Moritz, B.; Freericks, J. K.; Kemper, A. F.; Devereaux, T. P.

2017-11-01

Recent developments in the techniques of ultrafast pump-probe photoemission have made possible the search for collective modes in strongly correlated systems out of equilibrium. Including inelastic scattering processes and a retarded interaction, we simulate time- and angle-resolved photoemission spectroscopy (trARPES) to study the amplitude mode of a d -wave superconductor, a collective mode excited through the nonlinear light-matter coupling to the pump pulse. We find that the amplitude mode oscillations of the d -wave order parameter occur in phase at a single frequency that is twice the quasi-steady-state maximum gap size after pumping. We comment on the necessary conditions for detecting the amplitude mode in trARPES experiments.

Excited-State Vibrational Coherence in Perylene Bisimide Probed by Femtosecond Broadband Pump-Probe Spectroscopy.

PubMed

Son, Minjung; Park, Kyu Hyung; Yoon, Min-Chul; Kim, Pyosang; Kim, Dongho

2015-06-18

Broadband laser pulses with ultrashort duration are capable of triggering impulsive excitation of the superposition of vibrational eigenstates, giving rise to quantum beating signals originating from coherent wave packet motions along the potential energy surface. In this work, coherent vibrational wave packet dynamics of an N,N'-bis(2,6-dimethylphenyl)perylene bisimide (DMP-PBI) were investigated by femtosecond broadband pump-probe spectroscopy which features fast and balanced data acquisition with a wide spectral coverage of >200 nm. Clear modulations were observed in the envelope of the stimulated emission decay profiles of DMP-PBI with the oscillation frequencies of 140 and 275 cm(-1). Fast Fourier transform analysis of each oscillatory mode revealed characteristic phase jumps near the maxima of the steady-state fluorescence, indicating that the observed vibrational coherence originates from an excited-state wave packet motion. Quantum calculations of the normal modes at the low-frequency region suggest that low-frequency C-C (C═C) stretching motions accompanied by deformation of the dimethylphenyl substituents are responsible for the manifestation of such coherent wave packet dynamics.

Pump-probe studies of radiation induced defects and formation of warm dense matter with pulsed ion beams

NASA Astrophysics Data System (ADS)

Schenkel, T.; Persaud, A.; Gua, H.; Seidl, P. A.; Waldron, W. L.; Gilson, E. P.; Kaganovich, I. D.; Davidson, R. C.; Friedman, A.; Barnard, J. J.; Minior, A. M.

2014-10-01

We report results from the 2nd generation Neutralized Drift Compression Experiment at Berkeley Lab. NDCX-II is a pulsed, linear induction accelerator designed to drive thin foils to warm dense matter (WDM) states with peak temperatures of ~ 1 eV using intense, short pulses of 1.2 MeV lithium ions. Tunability of the ion beam enables pump-probe studies of radiation effects in solids as a function of excitation density, from isolated collision cascades to the onset of phase-transitions and WDM. Ion channeling is an in situ diagnostic of damage evolution during ion pulses with a sensitivity of <0.1% displacements per atom. We will report results from damage evolution studies in thin silicon crystals with Li + and K + beams. Detection of channeled ions tracks lattice disorder evolution with a resolution of ~ 1 ns using fast current measurements. We will discuss pump-probe experiments with pulsed ion beams and the development of diagnostics for WDM and multi-scale (ms to fs) access to the materials physics of collision cascades e.g. in fusion reactor materials. Work performed under auspices of the US DOE under Contract No. DE-AC02-05CH11231.

Chemical Probes of Histone Lysine Methyltransferases

PubMed Central

2015-01-01

Growing evidence suggests that histone methyltransferases (HMTs, also known as protein methyltransferases (PMTs)) play an important role in diverse biological processes and human diseases by regulating gene expression and the chromatin state. Therefore, HMTs have been increasingly recognized by the biomedical community as a class of potential therapeutic targets. High quality chemical probes of HMTs, as tools for deciphering their physiological functions and roles in human diseases and testing therapeutic hypotheses, are critical for advancing this promising field. In this review, we focus on the discovery, characterization, and biological applications of chemical probes for HMTs. PMID:25423077

Picosecond Transient Photoconductivity in Functionalized Pentacene Molecular Crystals Probed by Terahertz Pulse Spectroscopy

NASA Astrophysics Data System (ADS)

Hegmann, F. A.; Tykwinski, R. R.; Lui, K. P.; Bullock, J. E.; Anthony, J. E.

2002-11-01

We have measured transient photoconductivity in functionalized pentacene molecular crystals using ultrafast optical pump-terahertz probe techniques. The single crystal samples were excited using 800nm, 100fs pulses, and the change in transmission of time-delayed, subpicosecond terahertz pulses was used to probe the photoconducting state over a temperature range from 10 to 300K. A subpicosecond rise in photoconductivity is observed, suggesting that mobile carriers are a primary photoexcitation. At times longer than 4ps, a power-law decay is observed consistent with dispersive transport.

Photon-assisted Beam Probes for Low Temperature Plasmas and Installation of Neutral Beam Probe in Helimak

NASA Astrophysics Data System (ADS)

Garcia de Gorordo, Alvaro; Hallock, Gary A.; Kandadai, Nirmala

2008-11-01

The Heavy Ion Beam Probe (HIBP) diagnostic has successfully measured the electric potential in a number of major plasma devices in the fusion community. In contrast to a Langmuir probe, the HIBP measures the exact electric potential rather than the floating potential. It is also has the advantage of being a very nonperturbing diagnostic. We propose a new photon-assisted beam probe technique that would extend the HIBP type of diagnostics into the low temperature plasma regime. We expect this method to probe plasmas colder than 10 eV. The novelty of the proposed diagnostic is a VUV laser that ionizes the probing particle. Excimer lasers produce the pulsed VUV radiation needed. The lasers on the market don't have a short enough wavelength too ionize any ion directly and so we calculate the population density of excited states in a NLTE plasma. These new photo-ionization techniques can take an instantaneous one-dimensional potential measurement of a plasma and are ideal for nonmagnitized plasmas where continuous time resolution is not required. Also the status of the Neutral Beam Probe installation on the Helimak experiment will be presented.

Carrier-envelope phase effects for a dipolar molecule interacting with two-color pump-probe laser pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng Taiwang; Brown, Alex

2004-12-01

The interaction of a two-level dipolar molecule with two laser pulses, where one laser's frequency is tuned to the energy level separation (pump laser) while the second laser's frequency is extremely small (probe laser), is investigated. A dipolar molecule is one with a nonzero difference between the permanent dipole moments of the molecular states. As shown previously [A. Brown, Phys. Rev. A 66, 053404 (2002)], the final population transfer between the two levels exhibits a dependence on the carrier-envelope phase of the probe laser. Based on the rotating-wave approximation (RWA), an effective Hamiltonian is derived to account for the basicmore » characteristics of the carrier-envelope phase dependence effect. By analysis of the effective Hamiltonian, scaling properties of the system are found with regard to field strengths, pulse durations, and frequencies. According to these scaling properties, the final-state population transfer can be controlled by varying the carrier-envelope phase of the probe laser field using lasers with weak field strengths (low intensities) and relatively long pulse durations. In order to examine the possible roles of background states, the investigation is extended to a three-level model. It is demonstrated that the carrier-envelope phase effect still persists in a well-defined manner even when neighboring energy levels are present. These results illustrate the potential of utilizing excitation in dipolar molecules as a means of measuring the carrier-envelope phase of a laser pulse or if one can manipulate the carrier envelope phase, as a method of controlling population transfer in dipolar molecules. The results also suggest that the carrier-envelope phases must be taken into account properly when performing calculations involving pump-probe excitation schemes with laser frequencies which differ widely in magnitude.« less

Microwave-Based Oxidation State and Soot Loading Determination on Gasoline Particulate Filters with Three-Way Catalyst Coating for Homogenously Operated Gasoline Engines.

PubMed

Dietrich, Markus; Jahn, Christoph; Lanzerath, Peter; Moos, Ralf

2015-09-02

Recently, a novel method emerged to determine the oxygen storage degree of three way catalysts (TWC) by a microwave-based method. Up to now, this method has been investigated only in lab-scale reactors or under steady state conditions. This work expands those initial studies. A TWC-coated gasoline particulate filter was investigated in a dynamic engine test bench simulating a typical European driving cycle (NEDC). It could be shown that both the oxygen storage degree and the soot loading can be monitored directly, but not simultaneously due to their competitive effects. Under normal driving conditions, no soot accumulation was observed, related to the low raw emissions and the catalytic coating of the filter. For the first time, the quality factor of the cavity resonator in addition to the resonance frequency was used, with the benefit of less cross sensitivity to inconstant temperature and water. Therefore, a temperature dependent calibration of the microwave signal was created and applied to monitor the oxidation state in transient driving cycles. The microwave measurement mirrors the oxidation state determined by lambda probes and can be highly beneficial in start-stop phases (where lambda-probes do not work) and to determine the oxygen storage capacity (OSC) without unnecessary emissions.

Microwave-Based Oxidation State and Soot Loading Determination on Gasoline Particulate Filters with Three-Way Catalyst Coating for Homogenously Operated Gasoline Engines

PubMed Central

Dietrich, Markus; Jahn, Christoph; Lanzerath, Peter; Moos, Ralf

2015-01-01

Recently, a novel method emerged to determine the oxygen storage degree of three way catalysts (TWC) by a microwave-based method. Up to now, this method has been investigated only in lab-scale reactors or under steady state conditions. This work expands those initial studies. A TWC-coated gasoline particulate filter was investigated in a dynamic engine test bench simulating a typical European driving cycle (NEDC). It could be shown that both the oxygen storage degree and the soot loading can be monitored directly, but not simultaneously due to their competitive effects. Under normal driving conditions, no soot accumulation was observed, related to the low raw emissions and the catalytic coating of the filter. For the first time, the quality factor of the cavity resonator in addition to the resonance frequency was used, with the benefit of less cross sensitivity to inconstant temperature and water. Therefore, a temperature dependent calibration of the microwave signal was created and applied to monitor the oxidation state in transient driving cycles. The microwave measurement mirrors the oxidation state determined by lambda probes and can be highly beneficial in start-stop phases (where lambda-probes do not work) and to determine the oxygen storage capacity (OSC) without unnecessary emissions. PMID:26340629

On-line biofilm monitoring by "BIOX" electrochemical probe.

PubMed

Mollica, A; Cristiani, P

2003-01-01

The innovative electrochemical monitoring probe (BIOX) recently developed to improve the antifouling treatments of cooling systems in industrial plants is presented. On the basis of the good results obtained from applications on marine sites, some research has been stated to validate this technique in biofilm growth and prevention of microbial corrosion in fresh and drinking waters.

Nanoscience

DTIC Science & Technology

2011-07-22

L., Upgrading of Existing X - Ray Photoelectron Spectrometer Capabilities for Development and Analysis of Novel Energetic NanoCluster materials (DURIP...References From the Technical Reports database Allara, David L., Pennsylvania State University, Upgrading of Existing X - Ray Photoelectron...Scanning probe  X - ray Of these techniques, the most popularly used is the scanning probe, also known as the Dip-Pen Nanolithography (DPN) technique

Effect of Sequence Polymorphisms on Performance of Two Real-Time PCR Assays for Detection of Herpes Simplex Virus

PubMed Central

Stevenson, Jeffery; Hymas, Weston; Hillyard, David

2005-01-01

Herpes simplex virus (HSV) is the most common cause of acquired, sporadic encephalitis in the United States. PCR identification of HSV in spinal fluid has become the diagnostic gold standard due to its sensitivity and potential for speed, replacing other methods such as culture. We developed a real-time PCR assay to detect HSV, using a new type of hybridization probe, the Eclipse probe. In this study, we ran 323 samples (171 positives and 152 negatives) with the Eclipse real-time PCR assay and compared these results with another PCR assay using gel detection. The real-time assay agreed with our reference method for 319 out of the 323 samples tested (99%). Using two different real-time PCR platforms, we discovered that SNPs within the amplicon's probe binding region that are used to distinguish HSV-1 from HSV-2 can decrease assay sensitivity. This problem is potentially a general one for assays using fluorescent probes to detect target amplification in a real-time format. While real-time PCR can be a powerful tool in the field of infectious disease, careful sequence evaluation and clinical validation are essential in creating an effective assay. PMID:15872272

Storage and retrieval of light pulse in coupled quantum wells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Jibing, E-mail: liu0328@foxmail.com; Liu, Na; Shan, Chuanjia

In this paper, we propose an effective scheme to create a frequency entangled states based on bound-to-bound inter-subband transitions in an asymmetric three-coupled quantum well structure. A four-subband cascade configuration quantum well structure is illuminated with a pulsed probe field and two continuous wave control laser fields to generate a mixing field. By properly adjusting the frequency detunings and the intensity of coupling fields, the conversion efficiency can reach 100%. A maximum entangled state can be achieved by selecting a proper length of the sample. We also numerically investigate the propagation dynamics of the probe pulse and mixing pulse, themore » results show that two frequency components are able to exchange energy through a four-wave mixing process. Moreover, by considering special coupling fields, the storage and retrieval of the probe pulse is also numerically simulated.« less

Dynamics at Lys-553 of the acto-myosin interface in the weakly and strongly bound states.

PubMed Central

MacLean, J J; Chrin, L R; Berger, C L

2000-01-01

Lys-553 of skeletal muscle myosin subfragment 1 (S1) was specifically labeled with the fluorescent probe FHS (6-[fluorescein-5(and 6)-carboxamido]hexanoic acid succinimidyl ester) and fluorescence quenching experiments were carried out to determine the accessibility of this probe at Lys-553 in both the strongly and weakly actin-bound states of the MgATPase cycle. Solvent quenchers of varying charge [nitromethane, (2,2,6, 6-tetramethyl-1-piperinyloxy) (TEMPO), iodide (I(-)), and thallium (Tl(+))] were used to assess both the steric and electrostatic accessibilities of the FHS probe at Lys-553. In the strongly bound rigor (nucleotide-free) and MgADP states, actin offered no protection from solvent quenching of FHS by nitromethane, TEMPO, or thallium, but did decrease the Stern-Volmer constant by almost a factor of two when iodide was used as the quencher. The protection from iodide quenching was almost fully reversed with the addition of 150 mM KCl, suggesting this effect is ionic in nature rather than steric. Conversely, actin offered no protection from iodide quenching at low ionic strength during steady-state ATP hydrolysis, even with a significant fraction of the myosin heads bound to actin. Thus, the lower 50 kD subdomain of myosin containing Lys-553 appears to interact differently with actin in the weakly and strongly bound states. PMID:10692329

Structural changes of polyacids initiated by their neutralization with various alkali metal hydroxides. Diffusion studies in poly(acrylic acid)s.

PubMed

Masiak, Michal; Hyk, Wojciech; Stojek, Zbigniew; Ciszkowska, Malgorzata

2007-09-27

The changes in the three-dimensional structure of the poly(acrylic acid), PAA, induced by incorporation of various alkali-metal counterions have been evaluated by studying diffusion of an uncharged probe (1,1'-ferrocenedimethanol) in the polymeric media. The studies are supported by the measurements of conductivity and viscosity of the polymeric media. Solutions of linear PAA of four different sizes (molecular weights: 450,000, 750,000, 1,250,000, 4,000,000) were neutralized with hydroxides of alkali metals of group 1 of the periodic table (Li, Na, K, Rb, Cs) to the desired neutralization degree. The transport properties of the obtained polyacrylates were monitored by measuring the changes in the probe diffusion coefficient during the titration of the polyacids. The probe diffusivity was determined from the steady-state current of the probe voltammetric oxidation at disk microelectrodes. Diffusivity of the probe increases with the increase in the degree of neutralization and with the increase in viscosity. It reaches the maximum value at about 60-80% of the polyacid neutralization. The way the probe diffusion coefficients change is similar in all polyacid solutions and gels. The increase in the size of a metal cation causes, in general, an enhancement in the transport of probe molecules. The biggest differences in the probe diffusivities are between lithium and cesium polyacrylates. The differences between the results obtained for cesium and rubidium are not statistically significant due to lack of good precision of the voltammetric measurements. The measurements of the electric conductivity of polyacrylates and the theoretical predictions supplemented the picture of electrostatic interactions between the polyanionic chains and the metal cations of increasing size. In all instances of the PAAs, the viscosity of the solutions rapidly increases in the 0-60% range of neutralization and then becomes constant in the 60-100% region. With the exception of the shortest chain polyacid, the formation of a rigid medium (gel) has been observed in the experiments with all cations. After the end point of the titration was passed, a sudden drop in the viscosity and the disappearance of the gelatinous structure were seen. The largest value of viscosity has been recorded for the longest chain polyacid. The change in the cation of the strong base used did not affect the viscosity of the polymeric system.

Photochemical Kinetics of a Phosphine Oxide Free Radical Initiator from Femtosecond UV-Pump/Mid-IR-Probe Spectroscopy.

PubMed

Straub, Steffen; Lindner, Jörg; Vöhringer, Peter

2017-07-06

Femtosecond UV-pump/mid-infrared-probe spectroscopy was used to explore in detail the primary photochemical events of the free radical initiator, (2,4,6-trimethylbenzoyl)diphenylphosphine oxide, in liquid dichloromethane solution at room temperature. Following electronic excitation of its lowest excited singlet state, S 1 , the radical initiator undergoes an intersystem crossing to the triplet ground state, T 1 , with a time constant of 135 ps. A subsequent α-cleavage occurs from the triplet state with a time constant of 15 ps and yields a trimethylbenzoyl radical together with a diphenylphosphinoyl radical. Transient absorptions from the S 1 and T 1 states are observed that can be assigned to the P═O stretching mode and the symmetric in-plane deformation mode of the trimethylphenyl moiety of the radical initiator.

Information geometry of Gaussian channels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Monras, Alex; CNR-INFM Coherentia, Napoli; CNISM Unita di Salerno

2010-06-15

We define a local Riemannian metric tensor in the manifold of Gaussian channels and the distance that it induces. We adopt an information-geometric approach and define a metric derived from the Bures-Fisher metric for quantum states. The resulting metric inherits several desirable properties from the Bures-Fisher metric and is operationally motivated by distinguishability considerations: It serves as an upper bound to the attainable quantum Fisher information for the channel parameters using Gaussian states, under generic constraints on the physically available resources. Our approach naturally includes the use of entangled Gaussian probe states. We prove that the metric enjoys some desirablemore » properties like stability and covariance. As a by-product, we also obtain some general results in Gaussian channel estimation that are the continuous-variable analogs of previously known results in finite dimensions. We prove that optimal probe states are always pure and bounded in the number of ancillary modes, even in the presence of constraints on the reduced state input in the channel. This has experimental and computational implications. It limits the complexity of optimal experimental setups for channel estimation and reduces the computational requirements for the evaluation of the metric: Indeed, we construct a converging algorithm for its computation. We provide explicit formulas for computing the multiparametric quantum Fisher information for dissipative channels probed with arbitrary Gaussian states and provide the optimal observables for the estimation of the channel parameters (e.g., bath couplings, squeezing, and temperature).« less

Charge Transfer Dynamics at Dye-Sensitized ZnO and TiO2 Interfaces Studied by Ultrafast XUV Photoelectron Spectroscopy

PubMed Central

Borgwardt, Mario; Wilke, Martin; Kampen, Thorsten; Mähl, Sven; Xiao, Manda; Spiccia, Leone; Lange, Kathrin M.; Kiyan, Igor Yu.; Aziz, Emad F.

2016-01-01

Interfacial charge transfer from photoexcited ruthenium-based N3 dye molecules into ZnO thin films received controversial interpretations. To identify the physical origin for the delayed electron transfer in ZnO compared to TiO2, we probe directly the electronic structure at both dye-semiconductor interfaces by applying ultrafast XUV photoemission spectroscopy. In the range of pump-probe time delays between 0.5 to 1.0 ps, the transient signal of the intermediate states was compared, revealing a distinct difference in their electron binding energies of 0.4 eV. This finding strongly indicates the nature of the charge injection at the ZnO interface associated with the formation of an interfacial electron-cation complex. It further highlights that the energetic alignment between the dye donor and semiconductor acceptor states appears to be of minor importance for the injection kinetics and that the injection efficiency is dominated by the electronic coupling. PMID:27073060

The relationship between the macroscopic state of electrons and the properties of chorus waves observed by the Van Allen Probes

NASA Astrophysics Data System (ADS)

Yue, Chao; An, Xin; Bortnik, Jacob; Ma, Qianli; Li, Wen; Thorne, Richard M.; Reeves, Geoffrey D.; Gkioulidou, Matina; Mitchell, Donald G.; Kletzing, Craig A.

2016-08-01

Plasma kinetic theory predicts that a sufficiently anisotropic electron distribution will excite whistler mode waves, which in turn relax the electron distribution in such a way as to create an upper bound on the relaxed electron anisotropy. Here using whistler mode chorus wave and plasma measurements by Van Allen Probes, we confirm that the electron distributions are well constrained by this instability to a marginally stable state in the whistler mode chorus waves generation region. Lower band chorus waves are organized by the electron β∥e into two distinct groups: (i) relatively large-amplitude, quasi-parallel waves with β∥e≳0.025 and (ii) relatively small-amplitude, oblique waves with β∥e≲0.025. The upper band chorus waves also have enhanced amplitudes close to the instability threshold, with large-amplitude waves being quasi-parallel whereas small-amplitude waves being oblique. These results provide important insight for studying the excitation of whistler mode chorus waves.

Structure-based Design, Synthesis, Biochemical and Pharmacological Characterization of Novel Salvinorin A Analogues as Active State Probes of the κ-Opioid Receptor

PubMed Central

Yan, Feng; Bikbulatov, Ruslan V.; Mocanu, Viorel; Dicheva, Nedyalka; Parker, Carol E.; Wetsel, William C.; Mosier, Philip D.; Westkaemper, Richard B.; Allen, John A.; Zjawiony, Jordan K.; Roth, Bryan L.

2009-01-01

Salvinorin A, the most potent naturally occurring hallucinogen, has gained increasing attention since the κ-opioid receptor (KOR) was identified as its principal molecular target by us (Roth et al, PNAS, 2002). Here we report the design, synthesis and biochemical characterization of novel, irreversible, salvinorin A-derived ligands suitable as active state probes of the KOR. Based on prior substituted cysteine accessibility and molecular modeling studies, C3157.38 was chosen as a potential anchoring point for covalent labeling of salvinorin A-derived ligands. Automated docking of a series of potential covalently-bound ligands suggested that either a haloacetate moiety or other similar electrophilic groups could irreversibly bind with C3157.38. 22-thiocyanatosalvinorin A (RB-64) and 22-chlorosalvinorin A (RB-48) were both found to be extraordinarily potent and selective KOR agonists in vitro and in vivo. As predicted based on molecular modeling studies, RB-64 induced wash-resistant inhibition of binding with a strict requirement for a free cysteine in or near the binding pocket. Mass spectrometry (MS) studies utilizing synthetic KOR peptides and RB-64 supported the hypothesis that the anchoring residue was C3157.38 and suggested one biochemical mechanism for covalent binding. These studies provide direct evidence for the presence of a free cysteine in the agonist-bound state of KOR and provide novel insights into the mechanism by which salvinorin A binds to and activates KOR. PMID:19555087

Polycyclic aromatic hydrocarbons in stellar medium

NASA Astrophysics Data System (ADS)

Rastogi, Shantanu

2005-06-01

Polycyclic Aromatic Hydrocarbons (PAHs) are an important com- ponent of the Interstellar Medium (ISM). They are being used as probes for understanding of process and conditions of different astrophysical environments. The understanding of their IR spectra and its variations with PAH size and ionization state is useful in characterizing the ISM. Spectral features of model graphene sheets and also that of smaller PAH molecules are reported. The variation of intensity with charge state of the molecule shows that cations give a better correlation with observations. The relationship between changes in charge distribution with intensity changes upon ionization has been probed.

What does the dot-probe task measure? A reverse correlation analysis of electrocortical activity.

PubMed

Thigpen, Nina N; Gruss, L Forest; Garcia, Steven; Herring, David R; Keil, Andreas

2018-06-01

The dot-probe task is considered a gold standard for assessing the intrinsic attentive selection of one of two lateralized visual cues, measured by the response time to a subsequent, lateralized response probe. However, this task has recently been associated with poor reliability and conflicting results. To resolve these discrepancies, we tested the underlying assumption of the dot-probe task-that fast probe responses index heightened cue selection-using an electrophysiological measure of selective attention. Specifically, we used a reverse correlation approach in combination with frequency-tagged steady-state visual potentials (ssVEPs). Twenty-one participants completed a modified dot-probe task in which each member of a pair of lateralized face cues, varying in emotional expression (angry-angry, neutral-angry, neutral-neutral), flickered at one of two frequencies (15 or 20 Hz), to evoke ssVEPs. One cue was then replaced by a response probe, and participants indicated the probe orientation (0° or 90°). We analyzed the ssVEP evoked by the cues as a function of response speed to the subsequent probe (i.e., a reverse correlation analysis). Electrophysiological measures of cue processing varied with probe hemifield location: Faster responses to left probes were associated with weak amplification of the preceding left cue, apparent only in a median split analysis. By contrast, faster responses to right probes were systematically and parametrically predicted by diminished visuocortical selection of the preceding right cue. Together, these findings highlight the poor validity of the dot-probe task, in terms of quantifying intrinsic, nondirected attentive selection irrespective of probe/cue location. © 2018 Society for Psychophysiological Research.

Probing defect states in polycrystalline GaN grown on Si(111) by sub-bandgap laser-excited scanning tunneling spectroscopy

NASA Astrophysics Data System (ADS)

Hsiao, F.-M.; Schnedler, M.; Portz, V.; Huang, Y.-C.; Huang, B.-C.; Shih, M.-C.; Chang, C.-W.; Tu, L.-W.; Eisele, H.; Dunin-Borkowski, R. E.; Ebert, Ph.; Chiu, Y.-P.

2017-01-01

We demonstrate the potential of sub-bandgap laser-excited cross-sectional scanning tunneling microscopy and spectroscopy to investigate the presence of defect states in semiconductors. The characterization method is illustrated on GaN layers grown on Si(111) substrates without intentional buffer layers. According to high-resolution transmission electron microscopy and cathodoluminescence spectroscopy, the GaN layers consist of nanoscale wurtzite and zincblende crystallites with varying crystal orientations and hence contain high defect state densities. In order to discriminate between band-to-band excitation and defect state excitations, we use sub-bandgap laser excitation. We probe a clear increase in the tunnel current at positive sample voltages during sub-bandgap laser illumination for the GaN layer with high defect density, but no effect is found for high quality GaN epitaxial layers. This demonstrates the excitation of free charge carriers at defect states. Thus, sub-bandgap laser-excited scanning tunneling spectroscopy is a powerful complimentary characterization tool for defect states.

Spectroscopic Studies of the Super Relaxed State of Skeletal Muscle

PubMed Central

Naber, Nariman; Pate, Edward; Canton, Marcella; Reggiani, Carlo; Cooke, Roger

2016-01-01

In the super-relaxed state of myosin, ATPase activity is strongly inhibited by binding of the myosin heads to the core of the thick filament in a structure known as the interacting-heads motif. In the disordered relaxed state myosin heads are not bound to the core of the thick filament and have an ATPase rate that is 10 fold greater. In the interacting-heads motif the two regulatory light chains appear to bind to each other. We have made single cysteine mutants of the regulatory light chain, placed both paramagnetic and fluorescent probes on them, and exchanged them into skinned skeletal muscle fibers. Many of the labeled light chains tended to disrupt the stability of the super-relaxed state, and showed spectral changes in the transition from the disordered relaxed state to the super-relaxed state. These data support the putative interface between the two regulatory light chains identified by cryo electron microscopy and show that both the divalent cation bound to the regulatory light chain and the N-terminus of the regulatory light chain play a role in the stability of the super-relaxed state. One probe showed a shift to shorter wavelengths in the super-relaxed state such that a ratio of intensities at 440nm to that at 520nm provided a measure of the population of the super-relaxed state amenable for high throughput screens for finding potential pharmaceuticals. The results provide a proof of concept that small molecules that bind to this region can destabilize the super-relaxed state and provide a method to search for small molecules that do so leading to a potentially effective treatment for Type 2 diabetes and obesity. PMID:27479128

Probing Long-Range Configurations of Molecular Hydrogen

NASA Astrophysics Data System (ADS)

McCormack, Elizabeth

2011-05-01

Very long-range molecular configurations are of interest in a variety of contexts, for example, in the astro-chemistry of cold molecular clouds and in planetary atmospheres, including our own. Such states can be more than 10 times the size of the ground state and often possess energies above multiple ionization potentials and dissociation limits resulting in diverse and complex decay dynamics. Many of these configurations possess a double-well character arising from the interaction of molecular Rydberg states, repulsive doubly-excited states, and ionic states. The ion pair in hydrogen, an unusual molecular configuration consisting of one proton shrouded in a cloud of two electrons separated very far from the other proton, is notoriously difficult to create and study. We report results from on our investigation of such states using resonantly enhanced multi-photon ionization via the E,F v = 6, J = 0, 1, and 2 states to probe the H(n = 1) + H(n = 3) dissociation threshold energy region. Both molecular and atomic ion production were detected as a function of wavelength by using a time-of-flight mass spectrometer. Below threshold a series of highly excited vibrational levels of several long range states are observed. Above threshold broad resonances are observed with energies that agree well with the predictions of a mass-scaled Rydberg formula for bound states of the H+ H- ion pair. Measured linewidths, quantum defects, and rotational dependences are reported for ion pair principal quantum numbers in the range of n = 130 to 206. Our new results can be compared to recent experimental work using a different excitation scheme, which was the first spectroscopic observation of heavy Rydberg states in hydrogen, and new ab initio theoretical work. Supported by the National Science Foundation.

Probing solid catalysts under operating conditions: electrons or X-rays?

PubMed

Thomas, John Meurig; Hernandez-Garrido, Juan-Carlos

2009-01-01

Seeing is believing: In light of recent advances, the pros and cons of using electrons and X-rays for in situ studies of catalysts are analyzed: by using X-rays the structure of bound reactants at steady state are obtained from extended X-ray adsorption fine structure spectroscopy (EXAFS) data (see graph), thereby affording mechanistic insights.

Research at the Stanford Center for Radar Astronomy

NASA Technical Reports Server (NTRS)

1972-01-01

The research is reported in the applications of radar and radio techniques to the study of the solar system, and to space programs. Experiments reported include: bistatic-radar on Apollo missions, development of an unmanned geophysical observatory in the Antartic, Bragg scattering probes of sea states, characteristics of dense solar wind disturbances, and satellite communications for Alaska.

Solid State Cooling with Advanced Oxide Materials

DTIC Science & Technology

2014-06-03

Department of Materials Science and Engineering , Department of Mechanical Science and Engineering , and Department of Electrical and Computer... Engineering University of Illinois, Urbana-Champaign Program Overview The focus of this program was to probe electro-(magneto-)caloric materials for... engineering systems by developing theoretical and experimental approaches to study thermodynamic properties and effects in thin film systems. Despite

Real time monitoring of rat liver energy state during ischemia.

PubMed

Barbiro, E; Zurovsky, Y; Mayevsky, A

1998-11-01

Hepatic failure is one of the major problems developed during the posttransplantation period. A possible cause of hepatic failure is the prolonged ischemia induced during the implantation procedure. Hepatic ischemia leads to a reduction in oxygen supply, ATP level decline, liver metabolism impairment, and finally organ failure. The purpose of this study was to estimate the functional state of the liver by monitoring liver blood flow and the mitochondrial NADH redox state simultaneously and continuously during in situ liver ischemia followed by reperfusion. Measurements were performed using the multiprobe developed in our laboratory consisting of fibers for the measurement of relative liver blood flow (laser Doppler flowmetry) and mitochondrial redox state (NADH fluorescence). The experimental procedure included the temporary interruption of blood flow to the liver using three types of ischemia, hepatic artery occlusion, portal vein occlusion, and simultaneous occlusion of hepatic artery and portal vein, followed by a reperfusion period. These preliminary experiments showed a significant decrease in liver blood flow, following the three types of liver ischemia, and a significant increase in NADH levels. The probe used in this study incorporates the advantage of monitoring NADH and liver blood flow simultaneously and continuously from the same area on the surface of the liver. Since each of these two parameters is not calibrated in absolute units, the simultaneous monitoring decreases possible artifacts. Also, it will allow us to determine of the coupling between tissue blood flow and oxidative phosphorylation. It is believed that the measurements of respiratory chain dysfunction might predict organ viability in clinical organ transplantation situations. Using this probe may also help to decrease the variability in liver blood flow monitoring since liver blood flow monitoring is supported simultaneously with the mitochondrial redox state, which supplies the information on liver metabolic and functional state. Copyright 1998 Academic Press.

Fluorescence In Situ Hybridization Probe Validation for Clinical Use.

PubMed

Gu, Jun; Smith, Janice L; Dowling, Patricia K

2017-01-01

In this chapter, we provide a systematic overview of the published guidelines and validation procedures for fluorescence in situ hybridization (FISH) probes for clinical diagnostic use. FISH probes-which are classified as molecular probes or analyte-specific reagents (ASRs)-have been extensively used in vitro for both clinical diagnosis and research. Most commercially available FISH probes in the United States are strictly regulated by the U.S. Food and Drug Administration (FDA), the Centers for Disease Control and Prevention (CDC), the Centers for Medicare & Medicaid Services (CMS) the Clinical Laboratory Improvement Amendments (CLIA), and the College of American Pathologists (CAP). Although home-brewed FISH probes-defined as probes made in-house or acquired from a source that does not supply them to other laboratories-are not regulated by these agencies, they too must undergo the same individual validation process prior to clinical use as their commercial counterparts. Validation of a FISH probe involves initial validation and ongoing verification of the test system. Initial validation includes assessment of a probe's technical specifications, establishment of its standard operational procedure (SOP), determination of its clinical sensitivity and specificity, development of its cutoff, baseline, and normal reference ranges, gathering of analytics, confirmation of its applicability to a specific research or clinical setting, testing of samples with or without the abnormalities that the probe is meant to detect, staff training, and report building. Ongoing verification of the test system involves testing additional normal and abnormal samples using the same method employed during the initial validation of the probe.

Reply to "Comment on `Dynamics of slow light and light storage in a Doppler-broadened electromagnetically-induced-transparency medium: A numerical approach' "

NASA Astrophysics Data System (ADS)

Gou, Shih-Chuan; Su, Shih-Wei; Yu, Ite A.

2017-10-01

A damping term in the theoretical model of our paper [Phys. Rev. A 83, 013827 (2011), 10.1103/PhysRevA.83.013827] was questioned by the author of the Comment. The author argued this damping term cannot exactly describe the spontaneous decay or quantum jump process and, thus, concluded that our results are prone to be incorrect. However, the physics of electromagnetically induced transparency (EIT) is mainly determined by the ground-state coherence and the optical coherence of the probe transition. We show here that the damping term in our paper described the relaxation process of optical coherence in the EIT system, but not the spontaneous decay process of the population. The case of spontaneous decay used in the argument of the Comment is not an issue in typical EIT studies, in which the probe field is weak and treated as the perturbation. Furthermore, the experimental data in the paper were taken under the condition of a weak probe field. Our theoretical model in the weak-probe condition actually deals with the two coherences of EIT physics, and is suitable for analysis of the data. We believe the results of the study, focusing on the dynamics of slow light and light storage in Doppler-broadened EIT media, are correct.

Simulation of Mach Probes in Non-Uniform Magnetized Plasmas: the Influence of a Background Density Gradient

NASA Astrophysics Data System (ADS)

Haakonsen, Christian Bernt; Hutchinson, Ian H.

2013-10-01

Mach probes can be used to measure transverse flow in magnetized plasmas, but what they actually measure in strongly non-uniform plasmas has not been definitively established. A fluid treatment in previous work has suggested that the diamagnetic drifts associated with background density and temperature gradients affect transverse flow measurements, but detailed computational study is required to validate and elaborate on those results; it is really a kinetic problem, since the probe deforms and introduces voids in the ion and electron distribution functions. A new code, the Plasma-Object Simulator with Iterated Trajectories (POSIT) has been developed to self-consistently compute the steady-state six-dimensional ion and electron distribution functions in the perturbed plasma. Particle trajectories are integrated backwards in time to the domain boundary, where arbitrary background distribution functions can be specified. This allows POSIT to compute the ion and electron density at each node of its unstructured mesh, update the potential based on those densities, and then iterate until convergence. POSIT is used to study the impact of a background density gradient on transverse Mach probe measurements, and the results compared to the previous fluid theory. C.B. Haakonsen was supported in part by NSF/DOE Grant No. DE-FG02-06ER54512, and in part by an SCGF award administered by ORISE under DOE Contract No. DE-AC05-06OR23100.

Measurement of damping and temperature: Precision bounds in Gaussian dissipative channels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Monras, Alex; Illuminati, Fabrizio

2011-01-15

We present a comprehensive analysis of the performance of different classes of Gaussian states in the estimation of Gaussian phase-insensitive dissipative channels. In particular, we investigate the optimal estimation of the damping constant and reservoir temperature. We show that, for two-mode squeezed vacuum probe states, the quantum-limited accuracy of both parameters can be achieved simultaneously. Moreover, we show that for both parameters two-mode squeezed vacuum states are more efficient than coherent, thermal, or single-mode squeezed states. This suggests that at high-energy regimes, two-mode squeezed vacuum states are optimal within the Gaussian setup. This optimality result indicates a stronger form ofmore » compatibility for the estimation of the two parameters. Indeed, not only the minimum variance can be achieved at fixed probe states, but also the optimal state is common to both parameters. Additionally, we explore numerically the performance of non-Gaussian states for particular parameter values to find that maximally entangled states within d-dimensional cutoff subspaces (d{<=}6) perform better than any randomly sampled states with similar energy. However, we also find that states with very similar performance and energy exist with much less entanglement than the maximally entangled ones.« less

Mind wandering at the fingertips: automatic parsing of subjective states based on response time variability

PubMed Central

Bastian, Mikaël; Sackur, Jérôme

2013-01-01

Research from the last decade has successfully used two kinds of thought reports in order to assess whether the mind is wandering: random thought-probes and spontaneous reports. However, none of these two methods allows any assessment of the subjective state of the participant between two reports. In this paper, we present a step by step elaboration and testing of a continuous index, based on response time variability within Sustained Attention to Response Tasks (N = 106, for a total of 10 conditions). We first show that increased response time variability predicts mind wandering. We then compute a continuous index of response time variability throughout full experiments and show that the temporal position of a probe relative to the nearest local peak of the continuous index is predictive of mind wandering. This suggests that our index carries information about the subjective state of the subject even when he or she is not probed, and opens the way for on-line tracking of mind wandering. Finally we proceed a step further and infer the internal attentional states on the basis of the variability of response times. To this end we use the Hidden Markov Model framework, which allows us to estimate the durations of on-task and off-task episodes. PMID:24046753

Topology, edge states, and zero-energy states of ultracold atoms in one-dimensional optical superlattices with alternating on-site potentials or hopping coefficients

NASA Astrophysics Data System (ADS)

He, Yan; Wright, Kevin; Kouachi, Said; Chien, Chih-Chun

2018-02-01

One-dimensional superlattices with periodic spatial modulations of onsite potentials or tunneling coefficients can exhibit a variety of properties associated with topology or symmetry. Recent developments of ring-shaped optical lattices allow a systematic study of those properties in superlattices with or without boundaries. While superlattices with additional modulating parameters are shown to have quantized topological invariants in the augmented parameter space, we also found localized or zero-energy states associated with symmetries of the Hamiltonians. Probing those states in ultracold atoms is possible by utilizing recently proposed methods analyzing particle depletion or the local density of states. Moreover, we summarize feasible realizations of configurable optical superlattices using currently available techniques.

Objective Properties from Subjective Quantum States: Environment as a Witness

NASA Astrophysics Data System (ADS)

Ollivier, Harold; Poulin, David; Zurek, Wojciech H.

2004-11-01

We study the emergence of objective properties in open quantum systems. In our analysis, the environment is promoted from a passive role of a reservoir selectively destroying quantum coherence to an active role of amplifier selectively proliferating information about the system. We show that only preferred pointer states of the system can leave a redundant and therefore easily detectable imprint on the environment. Observers who—as is almost always the case—discover the state of the system indirectly (by probing a fraction of its environment) will find out only about the corresponding pointer observable. Many observers can act in this fashion independently and without perturbing the system. They will agree about its state. In this operational sense, preferred pointer states exist objectively.

Probing the Single-Particle Character of Rotational States in F 19 Using a Short-Lived Isomeric Beam

NASA Astrophysics Data System (ADS)

Santiago-Gonzalez, D.; Auranen, K.; Avila, M. L.; Ayangeakaa, A. D.; Back, B. B.; Bottoni, S.; Carpenter, M. P.; Chen, J.; Deibel, C. M.; Hood, A. A.; Hoffman, C. R.; Janssens, R. V. F.; Jiang, C. L.; Kay, B. P.; Kuvin, S. A.; Lauer, A.; Schiffer, J. P.; Sethi, J.; Talwar, R.; Wiedenhöver, I.; Winkelbauer, J.; Zhu, S.

2018-03-01

A beam containing a substantial component of both the Jπ=5+ , T1 /2=162 ns isomeric state of F 18 and its 1+, 109.77-min ground state is utilized to study members of the ground-state rotational band in F 19 through the neutron transfer reaction (d ,p ) in inverse kinematics. The resulting spectroscopic strengths confirm the single-particle nature of the 13 /2+ band-terminating state. The agreement between shell-model calculations using an interaction constructed within the s d shell, and our experimental results reinforces the idea of a single-particle-collective duality in the descriptions of the structure of atomic nuclei.

Probing Extreme-density Matter with Gravitational-wave Observations of Binary Neutron Star Merger Remnants

DOE Office of Scientific and Technical Information (OSTI.GOV)

Radice, David; Bernuzzi, Sebastiano; Pozzo, Walter Del

We present a proof-of-concept study, based on numerical-relativity simulations, of how gravitational waves (GWs) from neutron star merger remnants can probe the nature of matter at extreme densities. Phase transitions and extra degrees of freedom can emerge at densities beyond those reached during the inspiral, and typically result in a softening of the equation of state (EOS). We show that such physical effects change the qualitative dynamics of the remnant evolution, but they are not identifiable as a signature in the GW frequency, with the exception of possible black hole formation effects. The EOS softening is, instead, encoded in themore » GW luminosity and phase and is in principle detectable up to distances of the order of several megaparsecs with advanced detectors and up to hundreds of megaparsecs with third-generation detectors. Probing extreme-density matter will require going beyond the current paradigm and developing a more holistic strategy for modeling and analyzing postmerger GW signals.« less

High-Resolution Measurement of the Turbulent Frequency-Wavenumber Power Spectrum in a Laboratory Magnetosphere

NASA Astrophysics Data System (ADS)

Qian, T. M.; Mauel, M. E.

2017-10-01

In a laboratory magnetosphere, plasma is confined by a strong dipole magnet, where interchange and entropy mode turbulence can be studied and controlled in near steady-state conditions. Whole-plasma imaging shows turbulence dominated by long wavelength modes having chaotic amplitudes and phases. Here, we report for the first time, high-resolution measurement of the frequency-wavenumber power spectrum by applying the method of Capon to simultaneous multi-point measurement of electrostatic entropy modes using an array of floating potential probes. Unlike previously reported measurements in which ensemble correlation between two probes detected only the dominant wavenumber, Capon's ``maximum likelihood method'' uses all available probes to produce a frequency-wavenumber spectrum, showing the existence of modes propagating in both electron and ion magnetic drift directions. We also discuss the wider application of this technique to laboratory and magnetospheric plasmas with simultaneous multi-point measurements. Supported by NSF-DOE Partnership in Plasma Science Grant DE-FG02-00ER54585.

Femtosecond pump-probe photoionization-photofragmentation spectroscopy: photoionization-induced twisting and coherent vibrational motion of azobenzene cation.

PubMed

Ho, Jr-Wei; Chen, Wei-Kan; Cheng, Po-Yuan

2009-10-07

We report studies of ultrafast dynamics of azobenzene cation using femtosecond photoionization-photofragmentation spectroscopy. In our experiments, a femtosecond pump pulse first produces an ensemble of azobenzene cations via photoionization of the neutrals. A delayed probe pulse then brings the evolving ionic system to excited states that ultimately undergo ion fragmentation. The dynamics is followed by monitoring either the parent-ion depletion or fragment-ion formation as a function of the pump-probe delay time. The observed transients for azobenzene cation are characterized by a constant ion depletion modulated by a rapidly damped oscillatory signal with a period of about 1 ps. Theoretical calculations suggest that the oscillation arises from a vibration motion along the twisting inversion coordinate involving displacements in CNNC and phenyl-ring torsions. The oscillation is damped rapidly with a time constant of about 1.2 ps, suggesting that energy dissipation from the active mode to bath modes takes place in this time scale.

Probing the binding interaction of a phenazinium dye with serum transport proteins: a combined fluorometric and circular dichroism study.

PubMed

Bose, Debosreeta; Sarkar, Deboleena; Chattopadhyay, Nitin

2010-01-01

In the present investigation, an attempt has been made to study the interaction of phenosafranin (PSF), a cationic phenazinium dye with the transport proteins, bovine serum albumin (BSA) and human serum albumin (HSA), employing steady-state and time-resolved fluorometric and circular dichroism (CD) techniques. The photophysical properties of the dye are altered on binding with the serum proteins. An explicit study with respect to the modification of the fluorescence and fluorescence anisotropy upon binding, effect of denaturant, fluorescence lifetime and CD measurements reveal that the dye binds to both BSA and HSA with almost the same affinity. Far-UV CD spectra indicate a decrease in the percentage of alpha-helicity only for BSA upon binding with the probe. Near-UV CD responses indicate an alteration in the tertiary structure of both the transport proteins because of binding.

Simultaneous Optical Measurements of Axial and Tangential Steady-State Blade Deflections

NASA Technical Reports Server (NTRS)

Kurkov, Anatole P.; Dhadwal, Harbans S.

1999-01-01

Currently, the majority of fiber-optic blade instrumentation is being designed and manufactured by aircraft-engine companies for their own use. The most commonly employed probe for optical blade deflection measurements is the spot probe. One of its characteristics is that the incident spot on a blade is not fixed relative to the blade, but changes depending on the blade deformation associated with centrifugal and aerodynamic loading. While there are geometrically more complicated optical probe designs in use by different engine companies, this paper offers an alternate solution derived from a probe-mount design feature that allows one to change the probe axial position until the incident spot contacts either a leading or a trailing edge. By tracing the axial position of either blade edge one is essentially extending the deflection measurement to two dimensions, axial and tangential. The blade deflection measurements were obtained during a wind tunnel test of a fan prototype.

Sensitive fluorescence on-off probes for the fast detection of a chemical warfare agent mimic.

PubMed

Khan, Muhammad Shar Jhahan; Wang, Ya-Wen; Senge, Mathias O; Peng, Yu

2018-01-15

Two highly sensitive probes bearing a nucleophilic imine moiety have been utilized for the selective detection of chemical warfare agent (CWA) mimics. Diethyl chlorophosphate (DCP) was used as mimic CWAs. Both iminocoumarin-benzothiazole-based probes not only demonstrated a remarkable fluorescence ON-OFF response and good recognition, but also exhibited fast response times (10s) along with color changes upon addition of DCP. Limits of detection for the two sensors 1 and 2 were calculated as 0.065μM and 0.21μM, respectively, which are much lower than most other reported probes. These two probes not only show high sensitivity and selectivity in solution, but can also be applied for the recognition of DCP in the gas state, with significant color changes easily observed by the naked eye. Copyright © 2017 Elsevier B.V. All rights reserved.

Photonic switching based on the photoinduced birefringence in bacteriorhodopsin films

NASA Astrophysics Data System (ADS)

Huang, Yuhua; Wu, Shin-Tson; Zhao, Youyuan

2004-03-01

Photoinduced birefringence in bacteriorhodopsin films was investigated using pump-probe method and its application for photonic switching explored. A diode-pumped second-harmonic YAG laser was used as a pumping beam and a diode laser at λ=660 nm was used as a probing beam. The pump and probe beams overlap at the sample. Without the pumping beam, the probing light cannot transmit the analyzer to the detector. However, due to the photoinduced anisotropy, a portion of the probing light is detected when the pumping beam is present. Since λ=660 nm is far from the absorption peak (˜570 nm) of the ground state, the photoinduced birefringence predominates. Using the intensity-dependent photoinduced birefringence in a bacteriorhodopsin film, we have demonstrated a photonic switch with ˜1000:1 contrast ratio, ˜0.6 s rise time and ˜1.5 s decay time.

pathChirp: Efficient Available Bandwidth Estimation for Network Paths

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cottrell, Les

2003-04-30

This paper presents pathChirp, a new active probing tool for estimating the available bandwidth on a communication network path. Based on the concept of ''self-induced congestion,'' pathChirp features an exponential flight pattern of probes we call a chirp. Packet chips offer several significant advantages over current probing schemes based on packet pairs or packet trains. By rapidly increasing the probing rate within each chirp, pathChirp obtains a rich set of information from which to dynamically estimate the available bandwidth. Since it uses only packet interarrival times for estimation, pathChirp does not require synchronous nor highly stable clocks at the sendermore » and receiver. We test pathChirp with simulations and Internet experiments and find that it provides good estimates of the available bandwidth while using only a fraction of the number of probe bytes that current state-of-the-art techniques use.« less

System dynamics of subcellular transport.

PubMed

Chen, Vivien Y; Khersonsky, Sonya M; Shedden, Kerby; Chang, Young Tae; Rosania, Gus R

2004-01-01

In pharmacokinetic experiments, interpretations often hinge on treating cells as a "black box": a single, lumped compartment or boundary. Here, a combinatorial library of fluorescent small molecules was used to visualize subcellular transport pathways in living cells, using a kinetic, high content imaging system to monitor spatiotemporal variations of intracellular probe distribution. Most probes accumulate in cytoplasmic vesicles and probe kinetics conform to a nested, two-compartment dynamical system. At steady state, probes preferentially partition from the extracellular medium to the cytosol, and from the cytosol to cytoplasmic vesicles, with hydrophobic molecules favoring sequestration. Altogether, these results point to a general organizing principle underlying the system dynamics of subcellular, small molecule transport. In addition to plasma membrane permeability, subcellular transport phenomena can determine the active concentration of small molecules in the cytosol and the efflux of small molecules from cells. Fundamentally, direct observation of intracellular probe distribution challenges the simple boundary model of classical pharmacokinetics, which considers cells as static permeability barriers.

Probing the early stages of shock-induced chondritic meteorite formation at the mesoscale

PubMed Central

Rutherford, Michael E.; Chapman, David J.; Derrick, James G.; Patten, Jack R. W.; Bland, Philip A.; Rack, Alexander; Collins, Gareth S.; Eakins, Daniel E.

2017-01-01

Chondritic meteorites are fragments of asteroids, the building blocks of planets, that retain a record of primordial processes. Important in their early evolution was impact-driven lithification, where a porous mixture of millimetre-scale chondrule inclusions and sub-micrometre dust was compacted into rock. In this Article, the shock compression of analogue precursor chondrite material was probed using state of the art dynamic X-ray radiography. Spatially-resolved shock and particle velocities, and shock front thicknesses were extracted directly from the radiographs, representing a greatly enhanced scope of data than could be measured in surface-based studies. A statistical interpretation of the measured velocities showed that mean values were in good agreement with those predicted using continuum-level modelling and mixture theory. However, the distribution and evolution of wave velocities and wavefront thicknesses were observed to be intimately linked to the mesoscopic structure of the sample. This Article provides the first detailed experimental insight into the distribution of extreme states within a shocked powder mixture, and represents the first mesoscopic validation of leading theories concerning the variation in extreme pressure-temperature states during the formation of primordial planetary bodies. PMID:28555619

Subnanosecond spectrofluorimetry of new indolocarbazole derivatives in solutions and protein complexes and their dipole moments

NASA Astrophysics Data System (ADS)

Nemkovich, N. A.; Kruchenok, Yu. V.; Sobchuk, A. N.; Detert, H.; Wrobel, N.; Chernyavskiĭ, E. A.

2009-08-01

The spectral and temporal characteristics of new 6,12-dimethoxyindolo[3,2- b]carbazole, 5,11-dimethyl-6,12-dimethoxyindolo[3,2- b]carbazole, and 5,11-dihexyl-6,12-di(hexyloxy)indolo[3,2- b]carbazole fluorescence probes in organic solvents and protein complexes are studied. The dipole moments of indolocarbazoles in 1,4-dioxane were measured by electrooptical absorption method. The measured dipole moments have values within the range of (3.1-3.6) × 10-30 C m in the equilibrium ground state and increase to (4.8-5.6) × 10-30 C m after excitation. The excited state lifetime of indolocarbazole derivatives increases with increasing polarity and viscosity of the environment. The binding of indolocarbazoles with trypsinogen and human serum albumin increases the fluorescence intensity, changes the intensity ratio of fluorescence bands, and increases the average excited state lifetime of indolocarbazoles. The analysis of the instantaneous fluorescence spectra and fluorescence decay parameters at different wavelengths revealed the existence of several types of probe binding sites in proteins. It is found that the fluorescence characteristics of indolocarbazole derivatives depend on the conformation rearrangements of trypsinogen due to its thermal denaturation.

Preparation and Characterization of Fluorescent Derivatives of Chicken Egg White Lysozyme

NASA Technical Reports Server (NTRS)

Sumida, John; Forsythe, Elizabeth; Pusey, Marc

2000-01-01

Fluorescence is one of the most versatile and powerful tools for the study of macromolecules. While most proteins are intrinsically fluorescent, working at crystallization concentrations require the use of covalently prepared derivatives added as tracers. This approach requires derivatives that do not markedly affect the crystal packing. We have prepared a number of fluorescent derivatives of chicken egg white lysozyme with probes bound to one of two different sites on the protein molecule. Lucifer yellow, cascade blue, and 5-(2-aminoethyl)aminonapthalene-l-sulfonic acid (EDANS) have been attached to the side chain carboxyl of asp101 using a carbodiimide coupling procedure. asp101 lies within the active site cleft, and it is believed that the probes are at least partially "buried" within that cleft. Lucifer yellow and MANS probes with iodoacetamide reactive groups have been bound to hisl5, located on the "back side" of the molecule relative to the active site. The fluorescently labeled protein is readily purified from the starting material by cation exchange chromatography. All the derivatives fluoresce in both the solution and the crystalline states. Fluorescence characterization has focused on determining the bound probe quantum yields, lifetimes, absorption and emission spectra, and quenching by added solutes in comparison to the free probe. No appreciable changes are found in the lifetimes of any of the probes except for cascade blue, where Tau(sub free) = 3.52 ns vrs Tau(sub bound) = 2.8 ns. Spectral shifts are found in most cases. Particularly strong quenching upon binding is found in the case of the cascade blue derivative, likely due to probe interactions with the active site cleft. While none of the asp101 bound probes are well quenched by commonly employed solutes, such as potassium and sodium iodide, acrylamide, primuline, the chloride salts of manganese, cesium, and cobalt, trifluoroacetamide, trichloroethanol, and thallium iodide, in those cases where quenching is observed the bound probe is less efficiently quenched relative to the free probe. This indicates that the bound probes are less accessible to the bulk solution, an expected finding for attachment within the active site cleft. Attempts have been made to bind other molecules to these sites, with varying success. Interestingly, all three probes contain one or more sulfonate ((Ar-S03)-) groups. We have not been successful in binding analogous probes without sulfate groups such as pyrene, or with derivatized sulfonate groups such as dansyl type probes, analogous to MANS but where the sulfonate group is derivatized, Ar-S02-N2C2H7. None of the probes is rigidly bound to the protein, i.e., they all have a probe motion superimposed on that of the protein.

Controlling electronic couplings with tunable long wavelength pulses: Study of Autler-Townes splitting and XUV emission spectra

NASA Astrophysics Data System (ADS)

Harkema, Nathan; Liao, Chen-Ting; Sandhu, Arvinder

2017-04-01

Attosecond transient absorption spectroscopy (ATAS) enables the study of excited electron dynamics with unprecedented temporal and energy resolution. Many ATAS experiments use an extreme ultraviolet (XUV) pump pulse and a near-infrared (NIR) probe fixed at the fundamental laser frequency ( 800 nm) to study the light induced effects on electronic structure of atoms and molecules. We extend the technique by using an optical parametric amplifier in one arm of our setup, which allows us to independently tune the frequency of the probe pulse from 1200 to 1800 nm. These long-wavelength pulses allow us to explore a new regime, where we can control the couplings between nearby electronic states to alter the transient absorption lineshapes in atoms. We use this technique to investigate the 4p-3s detuning dependent Autler-Townes splitting of the 4p state in Helium. Light induced Floquet structures extending into the continuum are observed in our study. We demonstrate new tunable XUV emission channels from four-wave mixing processes, and the efficiency of these emissions can be strongly enhanced through resonant couplings. The tunable IR induced electronic couplings are also used to influence the autoionization dynamics in Argon. This work is supported by NSF Grant No. PHY-1505556 and ARO Grant No. W911NF-14-1-0383.

Collisional x- and A-State Kinetics of CN Using Transient Sub-Doppler Hole Burning

NASA Astrophysics Data System (ADS)

Hause, Michael L.; Sears, Trevor J.; Hall, Gregory E.

2010-06-01

We examine the collisional kinetics of the CN radical using transient hole-burning and saturation recovery. Narrow velocity groups of individual hyperfine levels in CN are depleted (X2Σ^+) and excited (A2Π) with a saturation laser, and probed by a counterpropagating, frequency modulated probe beam. Recovery of the unsaturated absorption is recorded following abrupt termination of an electro optically switched pulse of saturation light. Pressure-dependent recovery kinetics are measured for precursors, ethane dinitrile, NCCN, and pyruvonitrile, CH_3COCN, and buffer gases, helium, argon and nitrogen with rate coefficients ranging from 0.7-2.0 x 10-9 cm3 s-1 molec-1. In the case of NCCN, recovery kinetics are for two-level saturation resonances, where the signal observed is a combination of X- and A-state kinetics. Similar rates occur for three-level crossover resonances, which can be chosen to probe selectively the hole-filling in the X state or the decay of velocity-selected A state radicals. However in the case of CH_3COCN, which has a dipole moment of 3.45 D, the X-state kinetics are faster than the A-state due to an efficient dipole-dipole rotational energy transfer mechanism as the X-state dipole moment is 1.5 D and the A-state dipole moment is 0.06 D. The observed recovery rates are 2-3 times faster than the estimated rotationally inelastic contribution and are a combination of inelastic and velocity-changing elastic collisions. Acknowledgment: This work was carried out under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.

(1) Majorana fermions in pinned vortices; (2) Manipulating and probing Majorana fermions using superconducting circuits; and (3) Controlling a nanowire spin-orbit qubit via electric-dipole spin resonance

NASA Astrophysics Data System (ADS)

Nori, Franco

2014-03-01

We study a heterostructure which consists of a topological insulator and a superconductor with a hole. This system supports a robust Majorana fermion state bound to the vortex core. We study the possibility of using scanning tunneling spectroscopy (i) to detect the Majorana fermion in this setup and (ii) to study excited states bound to the vortex core. The Majorana fermion manifests itself as an H-dependent zero-bias anomaly of the tunneling conductance. The excited states spectrum differs from the spectrum of a typical Abrikosov vortex, providing additional indirect confirmation of the Majorana state observation. We also study how to manipulate and probe Majorana fermions using super-conducting circuits. In we consider a semiconductor nanowire quantum dot with strong spin-orbit coupling (SOC), which can be used to achieve a spin-orbit qubit. In contrast to a spin qubit, the spin-orbit qubit can respond to an external ac electric field, i.e., electric-dipole spin resonance. We develop a theory that can apply in the strong SOC regime. We find that there is an optimal SOC strength ηopt = √ 2/2, where the Rabi frequency induced by the ac electric field becomes maximal. Also, we show that both the level spacing and the Rabi frequency of the spin-orbit qubit have periodic responses to the direction of the external static magnetic field. These responses can be used to determine the SOC in the nanowire. FN is partly supported by the RIKEN CEMS, iTHES Project, MURI Center for Dynamic Magneto-Optics, JSPS-RFBR Contract No. 12-02-92100, Grant-in-Aid for Scientific Research (S), MEXT Kakenhi on Quantum Cybernetics, and the JSPS via its FIRST program.

Feedback control of plasma instabilities with charged particle beams and study of plasma turbulence

NASA Technical Reports Server (NTRS)

Tham, Philip Kin-Wah

1994-01-01

A new non-perturbing technique for feedback control of plasma instabilities has been developed in the Columbia Linear Machine (CLM). The feedback control scheme involves the injection of a feedback modulated ion beam as a remote suppressor. The ion beam was obtained from a compact ion beam source which was developed for this purpose. A Langmuir probe was used as the feedback sensor. The feedback controller consisted of a phase-shifter and amplifiers. This technique was demonstrated by stabilizing various plasma instabilities to the background noise level, like the trapped particle instability, the ExB instability and the ion-temperature-gradient (ITG) driven instability. An important feature of this scheme is that the injected ion beam is non-perturbing to the plasma equilibrium parameters. The robustness of this feedback stabilization scheme was also investigated. The principal result is that the scheme is fairly robust, tolerating about 100% variation about the nominal parameter values. Next, this scheme is extended to the unsolved general problem of controlling multimode plasma instabilities simultaneously with a single sensor-suppressor pair. A single sensor-suppressor pair of feedback probes is desirable to reduce the perturbation caused by the probes. Two plasma instabilities the ExB and the ITG modes, were simultaneously stabilized. A simple 'state' feedback type method was used where more state information was generated from the single sensor Langmuir probe by appropriate signal processing, in this case, by differentiation. This proof-of-principle experiment demonstrated for the first time that by designing a more sophisticated electronic feedback controller, many plasma instabilities may be simultaneously controlled. Simple theoretical models showed generally good agreement with the feedback experimental results. On a parallel research front, a better understanding of the saturated state of a plasma instability was sought partly with the help of feedback. A plasma instability is usually observed in its saturated state and appears as a single feature in the frequency spectrum with a single azimuthal and parallel wavenumbers. The physics of the non-zero spectral width was investigated in detail because the finite spectral width can cause "turbulent" transport. One aspect of the "turbulence" was investigated by obtaining the scaling of the linear growth rate of the instabilities with the fluctuation levels. The linear growth rates were measured with the established gated feedback technique. The research showed that the ExB instability evolves into a quasi-coherent state when the fluctuation level is high. The coherent aspects were studied with a bispectral analysis. Moreover, the single spectral feature was discovered to be actually composed of a few radial harmonics. The radial harmonics play a role in the nonlinear saturation of the instability via three-wave coupling.

Moderators of age effects on attention bias toward threat and its association with anxiety.

PubMed

Namaky, Nauder; Beltzer, Miranda L; Werntz, Alexandra J; Lambert, Ann E; Isaacowitz, Derek M; Teachman, Bethany A

2017-07-01

The current study used a research domain criteria (RDoC) approach to assess age differences in multiple indicators of attention bias and its ties to anxiety, examining stimulus domain and cognitive control as moderators of older adults' oft-cited positivity effect (bias towards positive and away from negative stimuli, when compared to younger adults). 38 Younger adults and 38 older adults were administered a battery of cognitive control and trait and state anxiety measures, and completed a dot-probe task to assess attention bias, during which reaction time and fixation duration (using eye-tracking) were recorded for negative and neutral social (a salient threat domain for younger adults) and physical (a salient threat domain for older adults) stimuli. Mixed-effects models demonstrated that older adults were faster to react to dot-probe trials when the probe appeared in the place of negative (vs. neutral) physical stimuli, but displayed no difference in reaction time for social stimuli. Also, older (vs. younger) adults with lower levels of cognitive control were less negatively biased in their visual fixation to social stimuli. A negative reaction time attention bias on the dot-probe task predicted greater trait anxiety among participants with low levels of cognitive control, with a more complex pattern predicting state anxiety. Older adults do attend to social and physical stimuli differently. When stimuli concern a social threat, older adults do not preferentially attend to either neutral or negative stimuli. However, when stimuli concern physical threat, older adults preferentially attend to negative stimuli. Threat biases are associated with anxiety at all ages for those with low cognitive control. Copyright © 2016. Published by Elsevier B.V.

Study of the relaxation rate of photoexcited indole molecules by the interferometric pump-and-probe method at picosecond resolution

NASA Astrophysics Data System (ADS)

Glazov, A. L.; Il'ina, A. D.; Sukharev, A. A.; Vasyutinskii, O. S.

2017-09-01

We present a new interferometric method that can be used for studying the dynamics of photoinduced processes in biologically important molecules at ultrahigh temporal resolution. The method is based upon the detection of changes in the refractive index of a substance excited by pulsed radiation of a femtosecond laser, which are measured by the pump-and-probe technique using time-delayed pulses of the same laser. The high sensitivity and stability of the interferometer allow this method to be used for monitoring variation of the concentration of short-lived excited states of biomolecules in solution. The proposed method has been verified by application to indole solutions in propylene glycol. The upper estimate of the lifetime of photoexcited indole molecules in solution amounted to about 40 ps.

Voltage-Driven Conformational Switching with Distinct Raman Signature in a Single-Molecule Junction.

PubMed

Bi, Hai; Palma, Carlos-Andres; Gong, Yuxiang; Hasch, Peter; Elbing, Mark; Mayor, Marcel; Reichert, Joachim; Barth, Johannes V

2018-04-11

Precisely controlling well-defined, stable single-molecule junctions represents a pillar of single-molecule electronics. Early attempts to establish computing with molecular switching arrays were partly challenged by limitations in the direct chemical characterization of metal-molecule-metal junctions. While cryogenic scanning probe studies have advanced the mechanistic understanding of current- and voltage-induced conformational switching, metal-molecule-metal conformations are still largely inferred from indirect evidence. Hence, the development of robust, chemically sensitive techniques is instrumental for advancement in the field. Here we probe the conformation of a two-state molecular switch with vibrational spectroscopy, while simultaneously operating it by means of the applied voltage. Our study emphasizes measurements of single-molecule Raman spectra in a room-temperature stable single-molecule switch presenting a signal modulation of nearly 2 orders of magnitude.

Pivot methods for global optimization

NASA Astrophysics Data System (ADS)

Stanton, Aaron Fletcher

A new algorithm is presented for the location of the global minimum of a multiple minima problem. It begins with a series of randomly placed probes in phase space, and then uses an iterative redistribution of the worst probes into better regions of phase space until a chosen convergence criterion is fulfilled. The method quickly converges, does not require derivatives, and is resistant to becoming trapped in local minima. Comparison of this algorithm with others using a standard test suite demonstrates that the number of function calls has been decreased conservatively by a factor of about three with the same degrees of accuracy. Two major variations of the method are presented, differing primarily in the method of choosing the probes that act as the basis for the new probes. The first variation, termed the lowest energy pivot method, ranks all probes by their energy and keeps the best probes. The probes being discarded select from those being kept as the basis for the new cycle. In the second variation, the nearest neighbor pivot method, all probes are paired with their nearest neighbor. The member of each pair with the higher energy is relocated in the vicinity of its neighbor. Both methods are tested against a standard test suite of functions to determine their relative efficiency, and the nearest neighbor pivot method is found to be the more efficient. A series of Lennard-Jones clusters is optimized with the nearest neighbor method, and a scaling law is found for cpu time versus the number of particles in the system. The two methods are then compared more explicitly, and finally a study in the use of the pivot method for solving the Schroedinger equation is presented. The nearest neighbor method is found to be able to solve the ground state of the quantum harmonic oscillator from a pure random initialization of the wavefunction.

Through-wafer optical probe characterization for microelectromechanical systems positional state monitoring and feedback control

NASA Astrophysics Data System (ADS)

Dawson, Jeremy M.; Chen, Jingdong; Brown, Kolin S.; Famouri, Parviz F.; Hornak, Lawrence A.

2000-12-01

Implementation of closed-loop microelectromechanical system (MEMS) control enables mechanical microsystems to adapt to the demands of the environment that they are actuating, opening a broad range of new opportunities for future MEMS applications. Integrated optical microsystems have the potential to enable continuous in situ optical interrogation of MEMS microstructure position fully decoupled from the means of mechanical actuation that is necessary for realization of feedback control. We present the results of initial research evaluating through-wafer optical microprobes for surface micromachined MEMS integrated optical position monitoring. Results from the through-wafer free-space optical probe of a lateral comb resonator fabricated using the multiuser MEMS process service (MUMPS) indicate significant positional information content with an achievable return probe signal dynamic range of up to 80% arising from film transmission contrast. Static and dynamic deflection analysis and experimental results indicate a through-wafer probe positional signal sensitivity of 40 mV/micrometers for the present setup or 10% signal change per micrometer. A simulation of the application of nonlinear sliding control is presented illustrating position control of the lateral comb resonator structure given the availability of positional state information.

Resolving the excited state equilibrium of peridinin in solution.

PubMed

Papagiannakis, Emmanouil; Larsen, Delmar S; van Stokkum, Ivo H M; Vengris, Mikas; Hiller, Roger G; van Grondelle, Rienk

2004-12-14

The carotenoid peridinin is abundant in the biosphere, as it is the main pigment bound by the light-harvesting complexes of dinoflagellates, where it collects blue and green sunlight and transfers energy to chlorophyll a with high efficiency. Its molecular structure is particularly complex, giving rise to an intricate excited state manifold, which includes a state with charge-transfer character. To disentangle the excited states of peridinin and understand their function in vivo, we applied dispersed pump-probe and pump-dump-probe spectroscopy. The preferential depletion of population from the intramolecular charge transfer state by the dump pulse demonstrates that the S(1) and this charge transfer state are distinct entities. The ensuing dump-induced dynamics illustrates the equilibration of the two states which occurs on the time scale of a few picoseconds. Additionally, the dump pulse populates a short-lived ground state intermediate, which is suggestive of a complex relaxation pathway, probably including structural reorientation or solvation of the ground state. These findings indicate that the unique intramolecular charge transfer state of peridinin is an efficient energy donor to chlorophyll a in the peridinin-chlorophyll-protein complex and thus plays a significant role in global light harvesting.

Atomic force microscopy of RNA: State of the art and recent advancements.

PubMed

Schön, Peter

2018-01-01

The atomic force microscope (AFM) has become a powerful tool for the visualization, probing and manipulation of RNA at the single molecule level. AFM measurements can be carried out in buffer solution in a physiological medium, which is crucial to study the structure and function of biomolecules, also allowing studying them at work. Imaging the specimen in its native state is a great advantage compared to other high resolution methods such as electron microscopy and X-ray diffraction. There is no need to stain, freeze or crystallize biological samples. Moreover, compared to NMR spectroscopy for instance, for AFM studies the size of the biomolecules is not limiting. Consequently the AFM allows one also to investigate larger RNA molecules. In particular, structural studies of nucleic acids and assemblies thereof, have been carried out by AFM routinely including ssRNA, dsRNA and nucleoprotein complexes thereof, as well as RNA aggregates and 2D RNA assemblies. These are becoming increasingly important as novel unique building blocks in the emerging field of RNA nanotechnology. In particular by AFM unique information can be obtained on these RNA based assemblies. Moreover, the AFM is of fundamental relevance to study biological relevant RNA interactions and dynamics. In this short review a brief overview will be given on structural studies that have been done related to AFM topographic imaging of RNA, RNA assemblies and aggregates. Finally, an overview on AFM beyond imaging will be provided. This includes force spectroscopy of RNA under physiological conditions in aqueous buffer to probe RNA interaction with proteins and ligands as well as other AFM tip based RNA probing. Important applications include the detection and quantification of RNA in biological samples. A selection of recent highlights and breakthroughs will be provided related to structural and functional studies by AFM. The main intention of this short review to provide the reader with a flavor of what AFM is able to contribute to RNA research and engineering. Copyright © 2017 Elsevier Ltd. All rights reserved.

The happy spotlight: positive mood and selective attention to rewarding information.

PubMed

Tamir, Maya; Robinson, Michael D

2007-08-01

Positive mood states are thought to sensitize individuals to rewards in their environment, presumably in the service of approach-related decision making and behavior. From a selective attention standpoint, such mood-related effects should be associated with selective attention biases favoring rewarding stimuli. No prior results along these lines have been reported. Therefore, the authors conducted a systematic program of research designed to document such relations. Study 1 found that daily positive mood states were associated with attention to reward words in a spatial probe task. Studies 2-5 replicated this association in the context of mood manipulations. The latter studies also show that the effect generalizes across different mood manipulation procedures, is specific to positive mood states, and is particularly apparent in relation to rewarding (vs. non-rewarding) positive stimuli. The results extend our knowledge of mood-cognition relations and have important implications for understanding the social cognitive consequences of positive mood states.

Electric dipole moments of the fluorescent probes Prodan and Laurdan: experimental and theoretical evaluations.

PubMed

Vequi-Suplicy, Cíntia C; Coutinho, Kaline; Lamy, M Teresa

2014-03-01

Several experimental and theoretical approaches can be used for a comprehensive understanding of solvent effects on the electronic structure of solutes. In this review, we revisit the influence of solvents on the electronic structure of the fluorescent probes Prodan and Laurdan, focusing on their electric dipole moments. These biologically used probes were synthesized to be sensitive to the environment polarity. However, their solvent-dependent electronic structures are still a matter of discussion in the literature. The absorption and emission spectra of Prodan and Laurdan in different solvents indicate that the two probes have very similar electronic structures in both the ground and excited states. Theoretical calculations confirm that their electronic ground states are very much alike. In this review, we discuss the electric dipole moments of the ground and excited states calculated using the widely applied Lippert-Mataga equation, using both spherical and spheroid prolate cavities for the solute. The dimensions of the cavity were found to be crucial for the calculated dipole moments. These values are compared to those obtained by quantum mechanics calculations, considering Prodan in vacuum, in a polarizable continuum solvent, and using a hybrid quantum mechanics-molecular mechanics methodology. Based on the theoretical approaches it is evident that the Prodan dipole moment can change even in the absence of solute-solvent-specific interactions, which is not taken into consideration with the experimental Lippert-Mataga method. Moreover, in water, for electric dipole moment calculations, it is fundamental to consider hydrogen-bonded molecules.