Transient Holes Research Articles

Can Light Alter the Yield of Plasmon-Driven Reactions on Gold and Gold-Palladium Nanoplates?

Noble-metal nanostructures, as well as their bimetallic analogues, catalyze a broad spectrum of plasmon-driven reactions. Catalytic properties of such nanostructures arise from light-generated surface plasmon resonances that decay forming transient hot electrons and holes. Hot carriers with "slower" dissipation rates accumulate on nanostructures generating an electrostatic potential. In this study, we examine whether light intensity can alter the electrostatic potential of mono- and bimetallic nanostructures changing yields of plasmon-driven reactions. Using tip-enhanced Raman spectroscopy (TERS), we quantified the yield of plasmon-driven transformations of 4-nitrobenzenethiol (4-NBT) and 3-mercaptobenzoic acid (3-MBA) on gold and gold-palladium nanoplates (AuNPs and Au@PdNPs, respectively). We found that on AuNPs 3-MBA decarboxylated forming thiophenol (TP), whereas 4-NBT was reduced to DMAB. The yield of both TP and DMAB gradually increased with increasing light intensity. On Au@PdNPs, 3-MBA could be reduced to 3-mercaptophenylmethanol (3-MPM), the yield of which was also directly dependent on the light intensity.

Effects of Chlorophyll Triplet States on the Kinetics of Spectral Hole Growth.

Spectral hole burning has been employed for decades to study various amorphous solids and proteins. Triplet states and respective transient holes were incorporated into theoretical models and software simulating nonphotochemical spectral hole burning (NPHB) and including all relevant distributions, in particular the distribution of the angle between the electric field of light E and transient dipole moment of the chromophore μ. The presence of a chlorophyll a triplet state with a lifetime of several milliseconds explains the slowdown of NPHB (on the depth vs illumination dose scale) with the increase of the light intensity, as well as larger hole depths observed in weak probe beam experiments, compared to those deduced from the hole growth kinetics (HGK) measurements (signal collected at a fixed wavelength while a stronger burning beam is on) in cytochrome b6f and chemically modified LH2. We also considered the solvent deuteration effects on triplet lifetime and concluded that both triplet states and local heating likely play a role in slowing down the HGK with increasing burn intensity.

Enabled/VASP is required to mediate proper sealing of opposing cardioblasts during Drosophila dorsal vessel formation.

The Drosophila dorsal vessel (DV) is comprised of two opposing rows of cardioblasts (CBs) that migrate toward the dorsal midline during development. While approaching the midline, CBs change shape, enabling dorsal and ventral attachments with their contralateral partners to create a linear tube with a central lumen. We previously demonstrated DV closure occurs via a "buttoning" mechanism where specific CBs advance ahead of their lateral neighbors, and attach creating transient holes, which eventually seal. Here, we investigate the role of the actin-regulatory protein enabled (Ena) in DV closure. Loss of Ena results in DV cell shape and alignment defects. Live analysis of DV formation in ena mutants shows a reduction in CB leading edge protrusion length and gaps in the DV between contralateral CB pairs. These gaps occur primarily between a specific genetic subtype of CBs, which express the transcription factor seven-up (Svp) and form the ostia inflow tracts of the heart. In WT embryos these gaps between Svp+ CBs are observed transiently during the final stages of DV closure. Our data suggest that Ena modulates the actin cytoskeleton in order to facilitate the complete sealing of the DV during the final stages of cardiac tube formation.

Tumor-Targeting Liposomes with Transient Holes Allowing Intact Rituximab Internally.

In this study, the strategy of transient generation of holes in the liposome surface has been shown to enable safe encapsulation of a high-molecular weight antibody (rituximab, Mw ∼140 kDa) within liposomes. These transient holes generated using our magnetoporation method allowed rituximab to safely enter the liposomes, and then the holes were plugged using hyaluronic acid grafted with 3-diethylaminopropylamine (DEAP). In the tumor microenvironment, the resulting liposomal rituximab was destabilized because of the ionization of the DEAP moiety at the acidic pH 6.5, resulting in extensive release of rituximab. Consequently, the rituximab released from the liposomes accumulated at high levels in tumors and bound to the CD20 receptors overexpressed on Burkitt lymphoma Ramos cells. This event led to significant enhancement in tumor cell ablation through rituximab-mediated complement-dependent cytotoxicity and Bcl-2 signaling inhibition-induced cell apoptosis.

Photothermally Activated Electrospun Nanofiber Mats for High-Efficiency Surface-Mediated Gene Transfection.

Although electrospun nanofibers have been used to deliver functional genes into cells attached to the surface of the nanofibers, the controllable release of genes from nanofibers and the subsequent gene transfection with high efficiency remain challenging. Herein, photothermally activated electrospun hybrid nanofibers are developed for high-efficiency surface-mediated gene transfection. Nanofibers with a core-sheath structure are fabricated using coaxial electrospinning. Plasmid DNA (pDNA) encoding basic fibroblast growth factor is encapsulated in the fiber core, and gold nanorods with photothermal properties are embedded in the fiber sheath composed of poly(l-lactic acid) and gelatin. The nanofiber mats show excellent and controllable photothermal response under near-infrared irradiation. The permeability of the nanofibers is thereby enhanced to allow the rapid release of pDNA. In addition, transient holes are formed in the membranes of NIH-3T3 fibroblasts attached to the mat, thus facilitating delivery and transfection with pDNA and leading to increased proliferation and migration of the transfected cells in vitro. This work offers a facile and reliable method for the regulation of cell function and cell behavior via localized gene transfection, showing great potential for application in tissue engineering and cell-based therapy.

Stochastic induction time of attachment due to the formation of transient holes in the intervening water films between air bubbles and solid surfaces

HypothesisBubble attachment to hydrophobic solid surfaces is influenced by the liquid film instability. Inclusion of transiently formed holes within the film rather than the so-called hydrophobic force in the theory is expected to better describe and explain film rupture and triple contact line formation in the bubble–surface attachment process. The significance of surface hydrophobicity and hole formation renders the stochastic nature of the induction time of attachment. ExperimentsA combination of high-speed video microscopy and theoretical analysis was applied to investigate the induction time of attachment and critical film thickness of air bubbles rising freely perpendicularly to silica surfaces of different hydrophobicities. FindingsFilm rupture occurred statistically for shorter induction times and thicker films on the more hydrophobic surface, rejecting the conjecture of hydrophobic force. Computed results of the critical base radius of the transient holes causing film rupture were merged together nicely, independently of surface hydrophobicity. The paper sheds light on the significance of hydrophobicity on the attachment process by means of a novel and easily implemented methodology, without relying on the debatable hydrophobic force.

(Invited) Intermediates in PEC Water Oxidation — How They Come and How They Go

Atmospheric oxygen that we live on is the result of a fundamental evolutionary step in photosynthesis which occurred on Earth 2-3 billion years ago [Biello 2009]. The water oxidation in natural photosystem II accounts for 50% of this oxygen. The man-made analog to this natural process is water oxidation in photoelectrochemical cells - one of the most complex processes in physical chemistry. I will showcase how modern x-ray spectroscopy methods have assisted in the understanding of the molecular pro-cesses which occur in natural [Bora 2013, Ralston 2000, Visser 2001] and in man-made "photosystems". A most recent example is the element and orbital specific identification of transient electron holes in iron oxide [Braun 2012], chemical surface intermediates [Bora 2011] and changes in the water molecules in the electrochemical double layer during photoelectrochemical water oxidation [Braun 2016]. I will also demonstrate how the electronic structure evolution is quantitatively paralleled by the electric transport properties of the electrodes during operation. [Biello 2009] Biello D: The Origin of Oxygen in Earth's Atmosphere. In Scientific American 2009. [Bora 2011] Bora DK et al. Journal of Physical Chemistry C 2011, 115:5619-5625. [Bora 2013] Bora DK et al. JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA 2013, 190:93-105. [Braun 2012] Braun A et al. Journal of Physical Chemistry C 2012, 116:16870-16875. [Braun 2016] Braun A et al. Catalysis Today 2016, 260:72-81. [Ralston 2000] Ralston CY et al. Journal of the American Chemical Society 2000, 122:10553-10560. [Visser 2001] Visser H et al. Journal of the American Chemical Society 2001, 123:7031-7039.

Solid-state NMR study of photocatalytic oxidation of acetaldehyde over the flame-made F-TiO2 catalyst

Solid-state 13C high-power proton decoupling (HPDEC), cross-polarization (CP), and 2-dimensional (2D) 13C-13C homonuclear correlation NMR techniques were used to study the adsorption of acetaldehyde on the flame-made fluorinated TiO2 (F-TiO2) catalyst, subsequent photocatalytic oxidation, and complete photo-decomposition at the presence of oxygen under UV light irradiation. Crotonaldehyde is formed via the acid-catalyzed aldol condensation through the adsorption of acetaldehyde on the F-TiO2 catalyst at room temperature without light illumination. At the presence of molecular oxygen as an electron acceptor, surface bonded acetaldehyde and crotonaldehyde are completely oxidized by the transient holes in the oxygen framework generated by UV light irradiation. This work provides clear evidence for the formation of crotonaldehyde, acetic acid, and formic acid, along with acetate and formate complexes. The identified surfaces complexes participate actively in the photocatalytic oxidation and do not play a significant role in the poisoning of the active sites, at least in such concentrations. The reaction pathways are therefore established.

Statistical Study of Solar Dimmings Using CoDiT

Abstract We present the results from analyzing the physical and morphological properties of 154 dimmings (transient coronal holes) and the associated flares and coronal mass ejections (CMEs). Each dimming in our 2013 catalog was processed with the semi-automated Coronal Dimming Tracker using Solar Dynamics Observatory AIA 193 Å observations and HMI magnetograms. Instead of the typically used difference images, we used our coronal hole detection algorithm to detect transient dark regions “directly” in extreme ultraviolet (EUV) images. This allowed us to study dimmings as the footpoints of CMEs—in contrast with the larger, diffuse dimmings seen in difference images that represent the projected view of the rising, expanding plasma. Studying the footpoint-dimming morphology allowed us to better understand the CME structure in the low corona. While comparing the physical properties of dimmings, flares, and CMEs we were also able to identify relationships between the different parts of this complex eruptive phenomenon. We found that larger dimmings are longer-lived, suggesting that it takes longer to “close down” large open magnetic regions. Also, during their growth phase, smaller dimmings acquire a higher magnetic flux imbalance (i. e., become more unipolar) than larger dimmings. Furthermore, we found that the EUV intensity of dimmings (indicative of local electron density) correlates with how much plasma was removed and how energetic the eruption was. Studying the morphology of dimmings (single, double, fragmented) also helped us identify different configurations of the quasi-open magnetic field.

Modeling Inductive Switching Characteristics of High-Speed Buffer Layer IGBT

In this study, a physics-based compact model for high-speed buffer layer insulated gate bipolar transistor (IGBT) is proposed. The model utilizes the 1-D Fourier-based solution of ambipolar diffusion equation (ADE) implemented in MATLAB and Simulink. Based on the improved understanding on the inductive switching behavior of a high-speed buffer layer IGBT, the ADE is solved for all injection levels instead of high-level injection only as usually done. Assuming high-level injection condition in the buffer layer, the excess carrier transport, redistribution and recombination in the buffer layer are redescribed. Moreover, some physical characteristics such as the low conductivity of N-base at turn-on transient and free holes appeared in the depletion layer during turn-off process are also considered in the model. Finally, the double-pulse switching tests for a commercial field stop IGBT and a light punch-through carrier-stored trench bipolar transistor are used to validate the proposed model. The simulation results are compared with experiment results and good agreement is obtained.

Abstract 2293: Vector-free engineering of immune cells for adoptive cell therapy

Abstract Ex vivo manipulation of the immune system for therapeutic purposes has shown incredible clinical promise with the advent of cell therapies such as Chimeric Antigen Receptor modified T-Cell Therapies (CAR-T). However expanding methods to manipulate cells beyond using plasmids and viruses requires a new delivery paradigm. Here we describe a microfluidic approach discovered at MIT where cells are mechanically deformed as they pass through a constriction smaller than the cell diameter. The resulting controlled application of compression and shear forces results in the formation of transient holes that enable the diffusion of material from the surrounding buffer directly into the cytosol. The method was recognized as one of the World Changing Ideas of 2014 by Scientific American since it has demonstrated the ability to deliver a range of material, such as nanoparticles and proteins to primary cells including embryonic stem cells and immune cells. This is in contrast to existing vector-based and physical methods that have limitations, including their reliance on exogenous materials or electrical fields, which can lead to toxicity or oncogenic off-target effects. Supporting the enabling potential of the new deformation based method, we previously reported that delivering protein transcription factors to primary fibroblasts produces a 10-fold improvement in induced pluripotent stem cell colony formation relative to electroporation and cell-penetrating peptides. In this work we describe the use of the vector-free technology to deliver antigen protein directly to the cytoplasm of antigen presenting cells to drive a powerful antigen specific T-cell response. Current efforts to use antigen presenting cells to drive T-cell responses rely on an inefficient process called cross-presentation that relies on material escaping the endosome and entering the cytoplasm. We believe that by delivering antigen directly to the cytoplasm of antigen presenting cells we can overcome this long standing barrier and drive powerful and specific T-cell responses. Our results show that by adoptively transferring antigen presenting cells that have antigen delivered into them we can drive a significant T-cell response. Specifically, we found that this results in a ∼50x increase in antigen specific T-cells in vivo when compared to endocytosis. This advance has the potential to dramatically enhance the therapeutic potential of therapeutic vaccination with antigenic material for the treatment of a wide variety of cancers. Indeed, the ability to deliver structurally diverse materials to difficult-to-transfect primary cells indicate that this method could potentially enable many novel clinical applications. Citation Format: Armon Sharei, Jonathan Gilbert, Darrell Irvine, Klavs Jensen, Robert Langer. Vector-free engineering of immune cells for adoptive cell therapy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2293.

Structural Heterogeneity in the Localized Excited States of Poly(3-hexylthiophene).

Transient hole-burning and resonantly enhanced Raman spectroscopies are used to probe heterogeneities among localized singlet excitons of poly(3-hexylthiophene) in solution. Transient hole-burning spectroscopy facilitated by population dumping through wavelength-selective stimulated emission exposes inhomogeneous broadening of the exciton absorption band in the near-infrared, as reflected by correlations between stimulated emission and excited-state absorption transition energies. Dump-induced spectral diffusion of the exciton absorption band reflects structural fluctuations in the locally excited polymer. This diffusion is observed to occur slightly faster or slower than the nonequilibrium relaxation that follows direct excitation of the polymer (8-9 ps), with the time scale for diffusion varying with subpopulation: dumping across small vs large band gaps results in diffusion over 5 vs 35 ps, respectively. Furthermore, incomplete spectral relaxation of transient holes reflects that subsets of locally excited structural motifs prepared through photoexcitation cannot interchange through structural fluctuations that occur over the singlet-exciton lifetime. Raman spectra of the C═C/C-C stretching region collected in resonance at energies across the exciton absorption band exhibit frequency and intensity trends (Raman "dispersion") ascribed to variation in the local effective conjugation length. Together, results explicitly reveal heterogeneities among excitonic states associated with variations and fluctuations in local conformational order.

ACCRETION FLOW DYNAMICS OF MAXI J1836-194 DURING ITS 2011 OUTBURST FROM TCAF SOLUTION

ABSTRACT The Galactic transient X-ray binary MAXI J1836-194 was discovered on 2011 August 29. Here we make a detailed study of the spectral and timing properties of its 2011 outburst using archival data from the RXTE Proportional Counter Array instrument. The evolution of accretion flow dynamics of the source during the outburst through spectral analysis with Chakrabarti–Titarchuk’s two-component advective flow (TCAF) solution as a local table model in XSPEC. We also fitted spectra with combined disk blackbody and power-law models and compared it with the TCAF model fitted results. The source is found to be in hard and hard-intermediate spectral states only during the entire phase of this outburst. No soft or soft-intermediate spectral states are observed. This could be due to the fact that this object belongs to a special class of sources (e.g., MAXI J1659-152, Swift J1753.5-0127, etc.) that have very short orbital periods and that the companion is profusely mass-losing or the disk is immersed inside an excretion disk. In these cases, flows in the accretion disk are primarily dominated by low viscous sub-Keplerian flow and the Keplerian rate is not high enough to initiate softer states. Low-frequency quasi-periodic oscillations (QPOs) are observed sporadically although as in normal outbursts of transient black holes, monotonic evolutions of QPO frequency during both rising and declining phases are observed. From the TCAF fits, we find the mass of the black hole in the range of 7.5–11 M ⊙, and from time differences between peaks of the Keplerian and sub-Keplerian accretion rates we obtain a viscous timescale for this particular outburst, ∼10 days.

Do transient white holes have a place in Nature?

The white-hole sector of Kruskal's solution is almost never used in physical applications. However, it can provide a radically different take on the gravitational collapse process, avoiding the problems appearing within the standard paradigm. In this contribution we will try to draw attention to some bouncing geometries that make a democratic usage of the black and white sectors of Kruskal's solution. We will argue that this type of behaviour could be perfectly natural in some approaches to the next physical level beyond classical General Relativity.

Black Hole Spin via Continuum Fitting and the Role of Spin in Powering Transient Jets

The spins of ten stellar black holes have been measured using the continuum-fitting method. These black holes are located in two distinct classes of X-ray binary systems, one that is persistently X-ray bright and another that is transient. Both the persistent and transient black holes remain for long periods in a state where their spectra are dominated by a thermal accretion disk component. The spin of a black hole of known mass and distance can be measured by fitting this thermal continuum spectrum to the thin-disk model of Novikov and Thorne; the key fit parameter is the radius of the inner edge of the black hole’s accretion disk. Strong observational and theoretical evidence links the inner-disk radius to the radius of the innermost stable circular orbit, which is trivially related to the dimensionless spin parameter a ∗ of the black hole (|a ∗|<1). The ten spins that have so far been measured by this continuum-fitting method range widely from a ∗≈0 to a ∗>0.95. The robustness of the method is demonstrated by the dozens or hundreds of independent and consistent measurements of spin that have been obtained for several black holes, and through careful consideration of many sources of systematic error. Among the results discussed is a dichotomy between the transient and persistent black holes; the latter have higher spins and larger masses. Also discussed is recently discovered evidence in the transient sources for a correlation between the power of ballistic jets and black hole spin.

A vector-free microfluidic platform for intracellular delivery

Intracellular delivery of macromolecules is a challenge in research and therapeutic applications. Existing vector-based and physical methods have limitations, including their reliance on exogenous materials or electrical fields, which can lead to toxicity or off-target effects. We describe a microfluidic approach to delivery in which cells are mechanically deformed as they pass through a constriction 30-80% smaller than the cell diameter. The resulting controlled application of compression and shear forces results in the formation of transient holes that enable the diffusion of material from the surrounding buffer into the cytosol. The method has demonstrated the ability to deliver a range of material, such as carbon nanotubes, proteins, and siRNA, to 11 cell types, including embryonic stem cells and immune cells. When used for the delivery of transcription factors, the microfluidic devices produced a 10-fold improvement in colony formation relative to electroporation and cell-penetrating peptides. Indeed, its ability to deliver structurally diverse materials and its applicability to difficult-to-transfect primary cells indicate that this method could potentially enable many research and clinical applications.

Emulsion ageing: effect on the dynamics of oil exchange in oil-in-water emulsions

Emulsions are highly dynamic entropically stabilised systems. In oil-in-water emulsions, it is generally believed that oil transfer from one droplet to another via a series of destabilisation processes (e.g. Ostwald ripening or coalescence) leads to droplet growth. Rapid oil exchange between oil droplets of toluene in toluene/Triton X-100/water emulsions was recently evidenced, without any measurable concomitant change in emulsion droplet size. This dynamic process is the result of oil permeation upon droplet collision through transient holes at the surface of the surfactant layer or via reversible partial coalescence of the oil droplets, i.e. a fusion/fission mechanism. The kinetics of the oil exchange can be monitored by pulsed field gradient-NMR. The time constant of the oil exchange equates to the critical NMR observation time, Δswitch. Here we probe this rapid oil exchange between droplets as a function of emulsion age. The timescale of emulsion ageing is determined from static light scattering and macroscopic phase separation data. The timescale of the dynamic oil exchange is extracted from the NMR data. The switching time Δswitch, is an increasing function of emulsion age. Three effects must be considered when explaining the kinetics of oil exchange as a function of emulsion age: (1) the increasing droplet size; larger droplets move more slowly and interact with one another less frequently leading to a decrease in both the collision frequency and the rate of oil exchange; (2) the increased droplet concentration that arises upon emulsion ageing, reducing the average distance between droplets and (3) the properties of the interfacial domain.

Sonoporation: Gene transfer using ultrasound.

Genes can be transferred using viral or non-viral vectors. Non-viral methods that use plasmid DNA and short interference RNA (siRNA) have advantages, such as low immunogenicity and low likelihood of genomic integration in the host, when compared to viral methods. Non-viral methods have potential merit, but their gene transfer efficiency is not satisfactory. Therefore, new methods should be developed. Low-frequency ultrasound irradiation causes mechanical perturbation of the cell membrane, allowing the uptake of large molecules in the vicinity of the cavitation bubbles. The collapse of these bubbles generates small transient holes in the cell membrane and induces transient membrane permeabilization. This formation of small pores in the cell membrane using ultrasound allows the transfer of DNA/RNA into the cell. This phenomenon is known as sonoporation and is a gene delivery method that shows great promise as a potential new approach in gene therapy. Microbubbles lower the threshold of cavity formation. Complexes of therapeutic genes and microbubbles improve the transfer efficiency of genes. Diagnostic ultrasound is potentially a suitable sonoporator because it allows the real-time monitoring of irradiated fields.

A complex state transition from the black hole candidate Swift J1753.5−0127

We present our monitoring campaign of the outburst of the black-hole candidate Swift J1753.5-0127, observed with the Rossi X-ray Timing Explorer and the Swift satellites. After ~4.5 years since its discovery, the source had a transition to the hard intermediate state. We performed spectral and timing studies of the transition showing that, unlike the majority of the transient black holes, the system did not go to the soft states but it returned to the hard state after a few months. During this transition Swift J1753.5-0127 features properties which are similar to those displayed by the black hole Cygnus X-1. We compared Swift J1753.5-0127 to one dynamically confirmed black hole and two neutron stars showing that its power spectra are in agreement with the binary hosting a black hole. We also suggest that the prolonged period at low flux that followed the initial flare is reminiscent of that observed in other X-ray binaries, as well as in cataclysmic variables.

AN EXTREME X-RAY DISK WIND IN THE BLACK HOLE CANDIDATE IGR J17091–3624

{\it Chandra} spectroscopy of transient stellar-mass black holes in outburst has clearly revealed accretion disk winds in soft, disk--dominated states, in apparent anti-correlation with relativistic jets in low/hard states. These disk winds are observed to be highly ionized, dense, and to have typical velocities of $\sim$1000 km/s or less projected along our line of sight. Here, we present an analysis of two {\it Chandra} High Energy Transmission Grating spectra of the Galactic black hole candidate IGR J17091$-$3624 and contemporaneous EVLA radio observations, obtained in 2011. The second {\it Chandra} observation reveals an absorption line at 6.91$\pm$0.01 keV; associating this line with He-like Fe XXV requires a blue-shift of $9300^{+500}_{-400}$ km/s (0.03$c$, or the escape velocity at 1000 R$_{Schw}$). This projected outflow velocity is an order of magnitude higher than has previously been observed in stellar-mass black holes, and is broadly consistent with some of the fastest winds detected in active galactic nuclei. A potential feature at 7.32 keV, if due to Fe XXVI, would imply a velocity of $\sim 14600$ km/s (0.05$c$), but this putative feature is marginal. Photoionization modeling suggests that the accretion disk wind in IGR J17091$-$3624 may originate within 43,300 Schwarzschild radii of the black hole, and may be expelling more gas than accretes. The contemporaneous EVLA observations strongly indicate that jet activity was indeed quenched at the time of our {\it Chandra} observations. We discuss the results in the context of disk winds, jets, and basic accretion disk physics in accreting black hole systems.