Passive Channel Research Articles

Power Budget Improvement in Passive Optical Networks Using PAM4 Hierarchical Modulation

Hierarchical PAM4 modulation in passive optical network downstream channels is experimentally demonstrated as a way to redistribute power margin between users with different path losses due to unequal fiber distribution and split losses. Using hierarchical PAM4 modulation the most-significant bit (MSB) and less-significant bit (LSB) can be assigned to two different optical network units (ONU) groups, whose receiver sensitivity can be optimized to increase the power budget of the ONUs with higher path losses, effectively redistributing power margin of the ONUs with lower losses. A single-threshold receiver is sufficient for the MSB ONU type and a dual-threshold receiver coupled with an and logic gate for the LSB ONU type, both of which are simpler than a full PAM4 receiver with three thresholds. Sensitivity improvement in a 25 Gb/s system is achieved using unequal signal level spacing and separate detection of the binary tributary streams of the PAM4 channel. Power budget increase of up to 3.5 dB is reported with respect to a standard PAM4 transmission. Higher chromatic dispersion tolerance is also measured for the higher sensitivity ONU group, enabling transmission over up to 40 km of single-mode fiber for the MSB ONUs with no chromatic dispersion compensation.

Media exposure and tobacco product addiction beliefs: Findings from the 2015 Health Information National Trends Survey (HINTS–FDA 2015)

BackgroundAddiction beliefs about tobacco use are associated with intentions to use and use of tobacco products. Exposure to information about tobacco products in media sources may affect addiction beliefs. PurposeTo examine the relationship between media exposure and tobacco product addiction beliefs. MethodsA nationally representative sample of US adults (n=3738) from the 2015 National Cancer Institute's Health Information National Trends Survey was used to examine addiction beliefs about cigarettes, cigars, smokeless tobacco, electronic cigarettes, hookah/waterpipe tobacco, and roll-your-own cigarettes. We used logistic regression to examine the relationship between media exposure and addiction beliefs. We defined media exposure by hours exposed, as well as exposure to tobacco use health effects information through media sources including social media. We categorized media sources by whether respondents actively or passively engaged with the source. FindingsA majority (60.6% to 87.3%) of respondents believed that cigarettes, cigars, roll-your-own cigarettes and smokeless tobacco are addictive. Less than half of respondents believed that electronic cigarettes or hookah/waterpipes are addictive (45.2% and 49.8%, respectively). Respondents exposed to messages about tobacco use health effects on active media channels (e.g., social media) had greater odds of believing that smokeless tobacco (adjusted odds ratio [AOR]=1.48), hookah/waterpipe (AOR=1.69), and roll-your-own cigarettes (AOR=1.61) are addictive. Respondents exposed to tobacco use health effects messages on passive media channels (e.g., television), had greater odds of believing that cigarettes (AOR=2.76) and electronic cigarettes (AOR=2.12) are addictive. ConclusionsUS adult exposure to information about the health effects of tobacco use was associated with addiction beliefs about tobacco products.

Energy Landscape Modeling of Escape Time Distributions Reveals the Molecular Mechanism of α-Synuclein Translocation through a VDAC Nanopore

Elucidating the motion of uniformly charged polymers in nanoscale channels has been a scientifically and technologically fruitful enterprise. It has long been recognized that underlying this motion is a free energy landscape to which both entropy and electrostatics contribute, but this landscape has proven difficult to measure experimentally. Here we use a non-uniformly charged “diblock copolymer”-like neuronal protein, α-synuclein, to probe the energy landscape governing passage through a nanoscale pore. α-Synuclein is a naturally occurring, intrinsically disordered polypeptide associated with Parkinson disease pathology and mitochondrial bioenergetics. The motion of this electrically heterogeneous polymer through an outer mitochondrial membrane passive transport channel, the voltage-dependent anion channel (VDAC), depends on the electrical and membrane association properties of both the charged and uncharged regions of α-synuclein. We introduce complementary models that describe this motion in two limits: first, a simple Markov model accounts for the simultaneous interaction of multiple α-synuclein molecules with VDAC for high membrane surface α-synuclein coverage. Second, the detailed energy landscape of this motion in the dilute limit can be reconstructed from the entropic, electrostatic, and membrane binding components by optimizing a drift-diffusion framework to the experimental data. The models predict the probability of α-synuclein translocation across VDAC pore, with immediate implications for the (patho-)physiological role of α-synuclein in mitochondrial functioning. Finally, we show that the time-dependent effect of α-synuclein on the electrical properties of VDAC reports on the motion of the junction between the charged and uncharged regions of the polymer through the pore.

Tubulin on Biomimetic Mitochondrial Membranes: Structural Features and Lipid Discrimination

Dimeric tubulin, an abundant cytosolic water-soluble protein, has emerged as an important regulatory factor of the permeability of the voltage-dependent anion channel (VDAC) in the mitochondrial outer membrane, with implications for mitochondrial energetics as well as the Warburg effect observed in cancer cells. A wealth of recent in vitro and in vivo evidence points to a mechanism of this regulation, in which a charged C-terminal tail of tubulin inserts into the water-filled VDAC pore, thus blocking metabolite fluxes through this passive transport channel. The membrane-binding properties of tubulin have proven difficult to ascertain, as early work generated contradictory results regarding the tubulin-membrane association, including whether it was integral or peripheral in nature. Here we report on a comprehensive biophysical study of tubulin binding to lipid membranes with compositions that mimic the mitochondrial outer membrane. A combination of surface plasmon resonance, bilayer overtone (second harmonics) analysis, and single-channel recordings show that tubulin distinguishes between lamellar and non-lamellar lipid components of the membrane. To obtain the structural features of the tubulin heterodimer on the membrane surface, we have employed neutron reflectometry (NR) of tubulin on a tethered bilayer lipid membrane platform. The NR results definitively show that tubulin binds peripherally, and in combination with molecular dynamics (MD) simulations suggest the binding domain to be a highly conserved amphipathic α-helix on α-tubulin. Thus tubulin joins a short but growing list of amphitropic proteins that target cell and organelle membranes by sensing lipid packing defects via amphipathic α-helices, suggesting a pathway by which lipid homeostasis regulates mitochondrial function.

Drug targets: ligand and voltage gated ion channels

The elucidation of a drug target is one of the earliest and most important steps in the drug discovery process. Ion channels encompassing both the ligand gated and voltage gated types are the second most common drug targets after G-Protein Coupled Receptors (GPCR). Ion channels are basically pore forming membrane proteins specialized for conductance of ions as per the concentration gradient. They are further broadly classified based on the energy (ATP) dependence into active ion channels/pumps and passive ion channels. Gating is the regulatory mechanism of these ion channels by which binding of a specific molecule or alteration in membrane potential induces conformational change in the channel architecture to result in ion flow or its inhibition. Thus, the study of ligand and voltage gated ion channels becomes an important tool for drug discovery especially during the initial stage of target identification. This review aims to describe the ligand and voltage gated ion channels along with discussion on its subfamilies, channel architecture and key pharmacological modulators.

Neutronic calculation of fast reactors by the EUCLID/V1 integrated code

This article considers neutronic calculation of a fast-neutron lead-cooled reactor BREST-OD-300 by the EUCLID/V1 integrated code. The main goal of development and application of integrated codes is a nuclear power plant safety justification. EUCLID/V1 is integrated code designed for coupled neutronics, thermomechanical and thermohydraulic fast reactor calculations under normal and abnormal operating conditions. EUCLID/V1 code is being developed in the Nuclear Safety Institute of the Russian Academy of Sciences. The integrated code has a modular structure and consists of three main modules: thermohydraulic module HYDRA-IBRAE/LM/V1, thermomechanical module BERKUT and neutronic module DN3D. In addition, the integrated code includes databases with fuel, coolant and structural materials properties. Neutronic module DN3D provides full-scale simulation of neutronic processes in fast reactors. Heat sources distribution, control rods movement, reactivity level changes and other processes can be simulated. Neutron transport equation in multigroup diffusion approximation is solved. This paper contains some calculations implemented as a part of EUCLID/V1 code validation. A fast-neutron lead-cooled reactor BREST-OD-300 transient simulation (fuel assembly floating, decompression of passive feedback system channel) and cross-validation with MCU-FR code results are presented in this paper. The calculations demonstrate EUCLID/V1 code application for BREST-OD-300 simulating and safety justification.

An engineered outer membrane pore enables an efficient oxygenation of aromatics and terpenes

Biocatalysis with cytochrome P450 enzymes are important for the industrial production of fine chemicals, pharmaceuticals, fragrance and flavor compounds since chemoselective hydroxylation of aromatics and terpenes are chemically difficult to achieve. A few P450 based industrial processes have been developed based on whole cell catalysis. However, the outer membrane of microbial cells forms an effective barrier, which reduces the uptake of hydrophobic substrates. The coexpression of outer membrane proteins in E. coli such as the ferric hydroxamate uptake protein (FhuA) can provide alternative solutions to chemical or physical methods for increasing compound flux through the outer membrane of E. coli and thereby to boost productivities. In this study we employed an engineered FhuA Δ1-160 variant in which the “cork domain” was removed (first 160 residues are deleted); FhuA Δ1-160 has a cross-section of 39–46Å with a “free” inner diameter of about 14 Å that serves as passive diffusion channel. FhuA WT and Δ1-160 were coexpressed on a bicistronic system with two P450 BM3 variants for regiospecific hydroxylation of aromatic compounds toluene and anisole as well as for oxidation of two terpenes (α)-pinene and (R)-(+)-limonene. The presence of FhuA Δ1‐160 resulted in a doubled product concentration for toluene (35μ to 50μM), anisole (25μM to 45μM), pinene (12μM to 20μM) and limonene (12μM to 25μM) and five times higher for the coumarin derivative BCCE. In order to characterizes and compensate for expression variations a quantification method based on Chromeo546-labled StrepTactinII was developed to quantify the number of FhuA Δ1-160 in the outer E. coli membrane (∼44000 of FhuA Δ1-160 per cell). Morphology studies showed that a 6% E. coli surface coverage can be achieved with FhuA Δ1‐160 without significantly influencing the E. coli rod shape. In summary, FhuA Δ1-160 efficiently increases uptake of hydrophobic aromatics and terpenes for whole-cell biotransformations and can likely be used for other enzymes and/or substrates.

Line-imaging VISAR for laser-driven equations of state experiments

The paper presents the diagnostic system for velocity measurements in laser- driven equations of state experiments. Two Mach-Zehnder line-imaging VISAR-type (velocity interferometer system for any reflector) interferometers form a vernier measuring system and can measure velocity in the interval of 5 to 50 km/s. Also, the system includes a passive channel that records target luminescence in the shock wave front. Spatial resolution of the optical layout is about 5 μm.

Effect of pulsed electric fields pre-treatment on mass transport during the osmotic dehydration of organic kiwifruit

Abstract Recently, some authors have applied pulsed electric fields (PEF) as a pre-treatment of osmotic dehydration, showing a faster kinetics of dehydration. Osmotic dehydration of fruit tissue shows complex mass transfer mechanism associated with active and passive transports of the vegetal matrix, usually driven by electrolytes. The aim of this work was to analyze the effect of different PEF values (100, 250, 400 V/cm) as a pre-treatment of the osmotic dehydration (61.5 °Bx, up to 120 min) on mass transport mechanism of organic kiwifruit. A thermodynamic model able to describe the mass transfer and tissue deformation in kiwifruit was developed. It was possible to conclude that pulsed electric field as a pre-treatment, remove a part of the native electrolytes, reducing the activity of protein active pumps, leaving alone the passive protein channels as a main mass transmembrane transport and therefore affecting to the regular functionality of cell homeostasis system. Industrial relevance This research develops a thermodynamic model able to describe mass transfer and kiwifruit deformation during OD and using PEF as a pre-treatment. Moreover, a deep analysis of active and passive mechanisms transports affected by PEF was done. The results of this research have demonstrated that PEF used as a pre-treatment of OD accelerated water mass transfer and removes part of the fruit natives electrolytes, affecting the functionality of the cell homeostasis system. Therefore, the present work represents an opportunity in the design of new candying products (less calories and sweetness).

PP.16.03] IS TRANSIENT RECEPTOR POTENTIAL VANILLOID TYPE 1 (TRPV1) A NEW TARGET FOR CARDIOPROTECTION?

Objective: Nowadays, cardiac arrest is a major cause of mortality in industrial countries. In France 120 000 persons are touched every year. Recently, it has been shown that isoflurane allows at the same time a pre- and a post-conditioning of the heart under experimental and clinical ischemic conditions in order to decrease infarct size (Landoni et al., 2013). Design and method: In the context of infarct, intracellular calcium overload is known to be one of the aggravating factors of ischemic injuries. Generally, isoflurane appears to modulate intracellular calcium content (Tampo et al., 2009). Calcium homeostasis is regulated by several Ca2+ pumps and channels located at the sarcolemma or at the reticulum membrane. Among them, we find calcium passive leak channels, such as TRPV1. In skeletal muscle, we recently demonstrated that TRPV1 is located in the longitudinal part of the SR and respond to pharmacological and physiological activations (Lotteau et al., 2013). We have also evidenced that TRPV1 is a potential target of isoflurane (unpublished data). Our hypothesis is that TRPV1 could similarly be one of the isoflurane targets in cardiac muscle. Results: Biochemical analysis and intracellular Ca2+ measurements were performed on cardiomyocytes from wild-type and TRPV1-KO mice. Our in vitro results show that: (i) TRPV1 is expressed in cardiac cells; (ii) an increase in intracellular calcium concentration ([Ca2+]i) is elicited under TRPV1 activation; (iii) TRPV1 could be a direct target of isoflurane. In parallel, our in vivo results indicate that a pharmacological preconditioning by isoflurane decrease the infarct size, probably though activation of TRPV1. Conclusions: According to the fact that TRPV1 activity can be modulated by a lot of pharmacological molecules and volatile anesthetics, this channel may serve as therapeutic target to reduce the infarct size.

Narrow Spectral Width FP Lasers for High-Speed Short-Reach Applications

While being cost effective and robust to external optical feedback, conventional Fabry–Perot (FP) semiconductor laser diodes cannot be used for fiber-optic communication systems beyond 1 Gb/s with span requirement over several kilometers due to the mode partition noise (MPN) caused by their multimode operation nature. In order to reduce the MPN-induced power penalty, we have proposed a narrow spectral width FP laser, which incorporates a built-in bandpass filter with its peak wavelength detuned from the material gain peak. Both simulation and experimental results show that this design can effectively narrow the root-mean-square width of the optical spectrum approximately by half. Within a given spectral width, we have also studied the impact of the number of longitudinal modes on the mode partition statistics k factor, aiming at further reducing the MPN-induced power penalty. The proposed laser exhibits noticeable better transmission performances over the conventional FP laser in simulation, and is expected to find its potential applications in high-speed short-reach, yet cost-sensitive fiber transmission systems, such as the passive optical access networks and Fibre channels for optical interconnection.

Detection and Parameter Estimation for Jitterbug Covert Channel Based on Coefficient of Variation

Jitterbug is a passive network covert timing channel supplying reliable stealthy transmission. It is also the basic manner of some improved covert timing channels designed for higher undetectability. The existing entropy-based detection scheme based on training sample binning may suffer from model mismatching, which results in detection performance deterioration. In this paper, a new detection method based on the feature of Jitterbug covert channel traffic is proposed. A fixed binning strategy without training samples is used to obtain bins distribution feature. Coefficient of variation (CV) is calculated for several sets of selected bins and the weighted mean is used to calculate the final CV value to distinguish Jitterbug from normal traffic. Furthermore, the timing window parameter of Jitterbug is estimated based on the detected traffic. Experimental results show that the proposed detection method can achieve high detection performance even with interference of network jitter, and the parameter estimation method can provide accurate values after accumulating plenty of detected samples.

Pupil Size Changes as an Active Information Channel for Biofeedback Applications.

Pupil size is usually regarded as a passive information channel that provides insight into cognitive and affective states but defies any further control. However, in a recent study (Ehlers et al. 2015) we demonstrate that sympathetic activity indexed by pupil dynamics allows strategic interference by means of simple cognitive techniques. Utilizing positive/negative imaginings, subjects were able to expand pupil diameter beyond baseline variations; albeit with varying degrees of success and only over brief periods. The current study provides a comprehensive replication on the basis of considerable changes to the experimental set-up. Results show that stricter methodological conditions (controlled baseline settings and specified user instructions) strengthen the reported effect, whereas overall performance increases by one standard deviation. Effects are thereby not restricted to pupillary level. Parallel recordings of skin conductance changes prove a general enhancement of induced autonomic arousal. Considering the stability of the results across studies, we conclude that pupil size information exceeds affective monitoring and may constitute an active input channel in human-computer interaction. Furthermore, since variations in pupil diameter reliably display self-induced changes in sympathetic arousal, the relevance of this parameter is strongly indicated for future approaches in clinical biofeedback.

0215 : Is Transient Receptor Potential Vanilloid Type 1 (TRPV1) a target of isoflurane in cardiomyocytes?

During a myocardial infarct, oxygen and nutrients deprivation triggers a reticular stress disrupting the Ca2+ balance of the cardiac cell. Several Ca2+ pumps and channels located at the sarcolemma or at the reticulum membrane are key players in this maintenance of Ca2+ homeostasis. Among them, we find passive leak channels, such as TRPs. Their involvement in myocardial ischemia-reperfusion injury has gained recognition recently, but the underlying mechanisms are not yet well understood. TRPV1 represents a non-selective cation channel that is activated by capsaicin, pH and high temperature. In skeletal muscle, we recently demonstrated that TRPV1 is located in the longitudinal part of the SR and respond to pharmacological and physiological activations (Lotteau et al., 2013). We questioned here whether TRPV1 might have a role in heart physiology. Biochemical analysis and intracellular Ca2+ measurements were performed on cardiomyocytes from wild-type and TRPV1-KO mice. Our in vitro results show that: (i) TRPV1 is expressed in cardiac cells; (ii) an increase in intracellular calcium concentration ([Ca2+]i) is elicited under TRPV1 activation; (iii) TRPV1 could be a direct target of isoflurane. In parallel, our in vivo results indicate that a pharmacological preconditioning by isoflurane decrease the infarct size, probably though activation of TRPV1. Ca2+ is central for the heart function, through its physiological role in excitation- contraction coupling, and the detrimental impact of Ca2+ overload during myocardial ischemia-reperfusion. It appears crucial to clarify the role of calcium leak channels such as TRPV1 channels in regulating Ca2+ homeostasis. According to the fact that TRPV1 activity can be modulated by a lot of pharmacological molecules, TRPV1 may serve as therapeutic target to reduce the infarct size. The author hereby declares no conflict of interest

Developmental Profile of Ion Channel Specializations in the Avian Nucleus Magnocellularis.

Ultrafast and temporally precise action potentials (APs) are biophysical specializations of auditory brainstem neurons; properties necessary for encoding sound localization and communication cues. Fundamental to these specializations are voltage dependent potassium (KV) and sodium (NaV) ion channels. Here, we characterized the functional development of these ion channels and quantified how they shape AP properties in the avian cochlear nucleus magnocellularis (NM). We report that late developing NM neurons (embryonic [E] days 19–21) generate fast APs that reliably phase lock to sinusoidal inputs at 75 Hz. In contrast, early developing neurons (<E12) have slower and less reliable APs that preferentially fire to lower frequencies (5–10 Hz). With development, the membrane time constant of NM neurons became faster, while input resistance and capacitance decreased. Change in input resistance was due to a 2-fold increase in KV current from E10 to E21 and when high-voltage activated potassium (K+HVA) channels were blocked, APs for all ages became significantly slower. This was most evident for early developing neurons where the ratio of K+HVA current accounted for ~85% of the total KV response. This ratio dropped to ~50% for late developing neurons, suggesting a developmental upregulation of low-voltage activated potassium (K+LVA) channels. Indeed, blockade of K+LVA eliminated remaining current and increased neural excitability for late developing neurons. We also report developmental changes in the amplitude, kinetics and voltage dependence of NaV currents. For early developing neurons, increase in NaV current amplitude was due to channel density while channel conductance dominated for late developing neurons. From E10 to E21, NaV channel currents became faster but differed in their voltage dependence; early developing neurons (<E16) had similar NaV channel inactivation voltages while late developing NM neurons (>E19) contained NaV channels that inactivate at more negative voltages, suggesting alterations in NaV channel subtypes. Taken together, our results indicate that the refinement of passive and active ion channel properties operate differentially in order to develop fast and reliable APs in the avian NM.

Local measurements and virtual pricing signals for residential demand side management

Demand side management and response schemes have the potential to reduce peak demand and improve grid utilization (improving the peak-to-base ratio). Existing methods often rely on accurate predictions or knowledge of the future demand, and most require a bi-directional communication infrastructure. This paper proposes two novel demand management approaches that do not have either of these requirements. The demand management problem is formulated as a constrained optimization problem to meet end-user energy demand subject to the physical limits of the electrical network. The adopted model focuses on the last mile of distribution networks and accounts for transformer load, line load and phase unbalance limitations. The optimization problem is solved iteratively, in a distributed and computationally tractable manner. In the first method, the behaviour of all users is coordinated through a time-varying price signal (a virtual price) that reflects how much power can be distributed given the network constraints. This virtual price signal is broadcast to all end-users by the Distribution Service Operator through a passive uni-directional communication channel. In the second method, an algorithm local to the user approximates the state of congestion in the network using the historical local voltage measurements. This method does not require a communication infrastructure. The performance of both methods is compared and their resulting behaviours are illustrated using a realistic simulation relevant to a typical Australian suburban low voltage distribution network.

Toward a biophysical understanding of the salt stress response of individual plant cells

We present and explore a kinetic model of ion transport across and between the membranes of an isolated plant cell with an emphasis on the cell's response to salt (Na+) stress. The vacuole, cytoplasm and apoplast are treated as concentric regions separated by tonoplast and plasma membranes. The model includes the transport of Na+, K+, Cl− and H+ across both membranes via primary active proton pumps, secondary active antiporters and symporters, as well as passive ion channels. In addition, water transport is included, allowing us to investigate both the osmotic and ionic components of salt stress. The model's predictions of steady state and transient cytosolic pH and Na+ concentrations were found to be quantitatively comparable to measured experimental values. Through an extensive simulation study we have identified and characterized scenarios in which individual transport processes (H+ pumps, Na+/H+ antiporters and channels involved in the transport of Na+) and their combinations have major effects on the level of Na+ in each of the cell compartments. This systematic study emulates the effects of overexpressing and inhibiting transporter genes by genetic modification and hence we have compared our simulations with observations from experiments conducted on transgenic plants. The simulations suggest that overexpressing tonoplast Na+/H+ antiporter genes and tonoplast H+ pump genes lead to an increase in the storage of Na+ in the vacuole (helping the cell to maintain water uptake under salt stress), with only a transient influence on the cytoplasmic Na+ concentration. The model predicts effects of varying the expression of transporter genes (individually or in combination) which have yet to be investigated in experiments. For example, our findings indicate that simultaneously overexpressing plasma membrane and tonoplast Na+/H+ antiporter genes would lead to improvements in both ionic and osmotic stress tolerance. The results demonstrate the importance of simultaneously modelling the transport of Na+ across both the tonoplast and plasma membrane, a task not undertaken previously.

Modeling Both Active and Passive Microwave Remote Sensing of Snow Using Dense Media Radiative Transfer (DMRT) Theory With Multiple Scattering and Backscattering Enhancement

In this paper, we incorporate the cyclical terms in dense media radiative transfer (DMRT) theory to model combined active and passive microwave remote sensing of snow over the same scene. The inclusion of cyclical terms is crucial if the DMRT is used to model both the active and passive contributions with the same model parameters. This is a necessity when setting out on a joint active/passive retrieval. Previously, the DMRT model has been applied to active and passive separately, and in each case with a separate set of model parameters. The traditional DMRT theory only includes the ladder terms of the Feynman diagrams. The cyclical terms are important in multiple volume scattering and volume–surface interactions. This leads to backscattering enhancement which represents itself as a narrow peak centered at backward direction. This effect is of less significance in passive remote sensing since emissivity is relating to the angular integral of bistatic scattering coefficients. The inclusion of cyclical terms in first-order radiative transfer (RT) accounts for the enhancement of the double bounce contribution and makes the results the same as that of distorted Born approximation in volume–surface interactions. In this paper, we develop the methodology of cyclical corrections within the framework of DMRT beyond first order to all orders of multiple scattering. The active DMRT equation is solved using a numerical iterative approach followed by cyclical corrections. Both quasi-crystalline approximation (QCA)–Mie theory with sticky spheres and bicontinuous media scattering model are used to illustrate the results. The cyclical correlation introduces around 1 dB increase in backscatter with a moderate snowpack optical thickness of ${\sim}\text{0.2}$ . The bicontinuous/DMRT model is next applied to compare with data acquired in the Nordic Snow Radar Experiment (NoSREx) campaign in the snow season of 2010–2011. The model results are validated against coincidental active and passive measurements using the same set of physical parameters of snow in all frequency and polarization channels. Results show good agreement in multiple active and passive channels.

Dynamics and Energy Contributions for Transport of Unfolded Pertactin through a Protein Nanopore.

To evaluate the physical parameters governing translocation of an unfolded protein across a lipid bilayer, we studied protein transport through aerolysin, a passive protein channel, at the single-molecule level. The protein model used was the passenger domain of pertactin, an autotransporter virulence protein. Transport of pertactin through the aerolysin nanopore was detected as transient partial current blockades as the unfolded protein partially occluded the aerolysin channel. We compared the dynamics of entry and transport for unfolded pertactin and a covalent end-to-end dimer of the same protein. For both the monomer and the dimer, the event frequency of current blockades increased exponentially with the applied voltage, while the duration of each event decreased exponentially as a function of the electrical potential. The blockade time was twice as long for the dimer as for the monomer. The calculated activation free energy includes a main enthalpic component that we attribute to electrostatic interactions between pertactin and the aerolysin nanopore (despite the low Debye length), plus an entropic component due to confinement of the unfolded chain within the narrow pore. Comparing our experimental results to previous studies and theory suggests that unfolded proteins cross the membrane by passing through the nanopore in a somewhat compact conformation according to the "blob" model of Daoud and de Gennes.

Fractional laser-assisted drug delivery: Active filling of laser channels with pressure and vacuum alteration.

Ablative fractional laser (AFXL) is rapidly evolving as one of the foremost techniques for cutaneous drug delivery. While AFXL has effectively improved topical drug-induced clearance rates of actinic keratosis, treatment of basal cell carcinomas (BCCs) has been challenging, potentially due to insufficient drug uptake in deeper skin layers. This study sought to investigate a standardized method to actively fill laser-generated channels by altering pressure, vacuum, and pressure (PVP), enquiring its effect on (i) relative filling of individual laser channels; (ii) cutaneous deposition and delivery kinetics; (iii) biodistribution and diffusion pattern, estimated by mathematical simulation. Franz diffusion chambers (FCs) were used to evaluate the PVP-technique, comparing passive (AFXL) and active (AFXL + PVP) channel filling. A fractional CO2-laser generated superficial (225 µm;17.5 mJ/channel) and deep (1200 µm; 130.5 mJ/channel) channels, and PVP was delivered as a 3-minutes cycle of 1 minute pressure (+1.0 atm), 1 minute vacuum (-1.0 atm), and 1 minute pressure (+1.0 atm). Filling of laser channels was visualized with a colored biomarker liquid (n = 12 FCs, n = 588 channels). Nuclear magnetic resonance quantified intracutaneous deposition of topically applied polyethylene glycol (PEG400) over time (10 minutes, 1 hour, and 4 hours), investigated with (n = 36 FCs) and without (n = 30 FCs) PVP-filling. Two-dimensional mathematical simulation was used to simulate intradermal biodistribution and diffusion at a depth of 1,000 µm. Active filling with application of PVP increased the number of filled laser channels. At a depth of 1,000 µm, filling increased from 44% (AFXL) to 94% with one PVP cycle (AFXL + PVP; P < 0.01). Active filling greatly enhanced intracutaneous deposition of PEG400, resulting in a rapid delivery six-folding uptake at 10 minutes (AFXL 54 µg/ml vs. AFXL + PVP 303 µg/ml, P < 0.01). AFXL alone generated an inhomogeneous uptake of PEG400, which greatly improved with active filling, resulting in a uniform uptake within the entire tissue. Active filling with PVP secures filling of laser channels and induces a deeper, greater, more rapid delivery than conventional AFXL. This delivery technique has promise to improve treatment efficacy for medical treatments of dermally invasive lesions, such as BCCs.