Exponential Decay Fitting Research Articles

Superfluorescence and nonlinear optical response of CH3NH3PbBr3-based mesostructures: applications to amplified spontaneous emission and ultrafast lasers.

Metal halide perovskites have unique luminescent properties that make them an attractive alternative for high quality light-emitting devices. However, the poor stability of perovskites with many defects and the long cycle time for the preparation of perovskite nanocomposites have hindered their production and application. Here, we prepared the perovskite mesostructures by embedding MAPbBr3 nanocrystals in the mesopores on the surface of silica nanospheres and mixing the nanospheres with silver nanowires and poly(methyl methacrylate) (PMMA), and further explored their optical properties. The perovskite mesostructures exhibited superfluorescence (SF) under 785 nm laser excitation and the decay time was as short as 0.59 ps using a double exponential decay fit. The optical nonlinearity of these perovskite mesostructures under two-photon excitation was investigated by the Z-scanning technique. The samples exhibited both two-photon absorption (TPA) and saturation absorption (SA) with nonlinear absorption coefficients β ranging approximately 0.15 to 0.89 cm/GW corresponding to the TPA, and a saturation intensity of about 0.026 GW/cm2 was determined. In addition, the quality of the perovskite mesostructures was shown to be significantly improved, including an increase in radiative efficiency and an extension of the optical gain lifetime. The samples were excited by a two-photon femtosecond laser pump at room temperature and atmospheric pressure, and the laser peak appeared at 540.1 nm with a low amplified spontaneous emission (ASE) threshold of 0.52 mJ/cm2. Moreover, the perovskite mesostructures have been added to the fiber laser system as a saturable absorber, and the Q-switched pulse is generated at the wavelength of 1.5 µm. Our work effectively demonstrates that perovskite mesostructured materials can be functionalized for photonic devices, paving the way for further exploration of complex, functional and practical perovskite.

A new method for estimating megacity NOx emissions and lifetimes from satellite observations

Abstract. We present a new method for estimating NOx emissions and effective lifetimes from large cities based on NO2 measurements from the TROPOspheric Monitoring Instrument (TROPOMI) (PAL dataset, May 2018–November 2021). As in previous studies, the estimate is based on the downwind plume evolution for different wind directions separately. The novelty of the presented approach lies in the simultaneous fit of downwind patterns for opposing wind directions, which makes the method far more robust (i.e., less prone to local minima with nonphysically high or low lifetimes) than a single exponential decay fit. In addition, the new method does not require the assumption of a city being a “point source” but also derives the spatial distribution of emissions. The method was successfully applied to 100 cities worldwide on a seasonal scale. Fitted emissions generally agree reasonably with the Emissions Database for Global Atmospheric Research (EDGAR) v6 (R=0.72) and are on average 14 % lower, while estimated uncertainties are still rather large (≈ 30 %–50 %). Lifetimes were found to be rather short (2.44 ± 0.68 h) and show no distinct dependency on season or latitude, which might be a consequence of discarding observations at high solar zenith angles (>65°). The main limitations of this and similar methods are the underlying assumptions of steady state (meaning constant emissions, wind fields and chemical conditions) within about 100 km downwind from a city, which is probably a simplification that is too strong in order to reach higher accuracies.

3D convolutional neural networks predict cellular metabolic pathway use from fluorescence lifetime decay data.

Fluorescence lifetime imaging of the co-enzyme reduced nicotinamide adenine dinucleotide (NADH) offers a label-free approach for detecting cellular metabolic perturbations. However, the relationships between variations in NADH lifetime and metabolic pathway changes are complex, preventing robust interpretation of NADH lifetime data relative to metabolic phenotypes. Here, a three-dimensional convolutional neural network (3D CNN) trained at the cell level with 3D NAD(P)H lifetime decay images (two spatial dimensions and one time dimension) was developed to identify metabolic pathway usage by cancer cells. NADH fluorescence lifetime images of MCF7 breast cancer cells with three isolated metabolic pathways, glycolysis, oxidative phosphorylation, and glutaminolysis were obtained by a multiphoton fluorescence lifetime microscope and then segmented into individual cells as the input data for the classification models. The 3D CNN models achieved over 90% accuracy in identifying cancer cells reliant on glycolysis, oxidative phosphorylation, or glutaminolysis. Furthermore, the model trained with human breast cancer cell data successfully predicted the differences in metabolic phenotypes of macrophages from control and POLG-mutated mice. These results suggest that the integration of autofluorescence lifetime imaging with 3D CNNs enables intracellular spatial patterns of NADH intensity and temporal dynamics of the lifetime decay to discriminate multiple metabolic phenotypes. Furthermore, the use of 3D CNNs to identify metabolic phenotypes from NADH fluorescence lifetime decay images eliminates the need for time- and expertise-demanding exponential decay fitting procedures. In summary, metabolic-prediction CNNs will enable live-cell and in vivo metabolic measurements with single-cell resolution, filling a current gap in metabolic measurement technologies.

Comparison of phasor analysis and biexponential decay curve fitting of autofluorescence lifetime imaging data for machine learning prediction of cellular phenotypes.

Introduction: Autofluorescence imaging of the coenzymes reduced nicotinamide (phosphate) dinucleotide (NAD(P)H) and oxidized flavin adenine dinucleotide (FAD) provides a label-free method to detect cellular metabolism and phenotypes. Time-domain fluorescence lifetime data can be analyzed by exponential decay fitting to extract fluorescence lifetimes or by a fit-free phasor transformation to compute phasor coordinates. Methods: Here, fluorescence lifetime data analysis by biexponential decay curve fitting is compared with phasor coordinate analysis as input data to machine learning models to predict cell phenotypes. Glycolysis and oxidative phosphorylation of MCF7 breast cancer cells were chemically inhibited with 2-deoxy-d-glucose and sodium cyanide, respectively; and fluorescence lifetime images of NAD(P)H and FAD were obtained using a multiphoton microscope. Results: Machine learning algorithms built from either the extracted lifetime values or phasor coordinates predict MCF7 metabolism with a high accuracy (∼88%). Similarly, fluorescence lifetime images of M0, M1, and M2 macrophages were acquired and analyzed by decay fitting and phasor analysis. Machine learning models trained with features from curve fitting discriminate different macrophage phenotypes with improved performance over models trained using only phasor coordinates. Discussion: Altogether, the results demonstrate that both curve fitting and phasor analysis of autofluorescence lifetime images can be used in machine learning models for classification of cell phenotype from the lifetime data.

An optimization method for surface urban heat island footprint extraction based on anisotropy assumption

The footprint (FP) is the main indicator used to quantitatively analyse the surface urban heat island (SUHI) effect. Currently, SUHI FP extraction methods ignore the interference caused by the city shape and are mostly based on the isotropic expansion assumption, resulting in an exaggerated range. Therefore, a new approach for an optimization schema that leverages the assumptions of angle segmentation and anisotropy is proposed herein. This method divides an urban area and its buffer rings into 16 sectors with equal central angles and selects appropriate land surface temperature (LST) curves for an exponential decay fit. The final FP was determined using the SUHI extension distance and the reference rural LST. To verify the effectiveness of this method, SUHI FPs of 27 cities in the central region of the Yangtze River Delta (YRD) were extracted during the summer of 2019, and the results were compared with those derived from traditional methods. The results showed that the FPs calculated using this method were more detailed because they minimized the influence of urban shape, topography, and the surrounding landscape. Moreover, this method played a vital role in revealing the effect of the land use allocation outside urban area on the SUHI effect. This state-of-the-art method is useful for unveiling SUHI spatial distribution patterns and for providing scientific support for land planning for sustainable urban development.

Chiral-Controlled Cyclic Chemiluminescence Reactions for the Analysis of Enantiomer Amino Acids

The similarity and complexity of chiral amino acids (AAs) in complex samples remain a significant challenge in their analysis. In this work, the chiral metal-organic framework (MOF)-controlled cyclic chemiluminescence (CCL) reaction is developed and utilized in the analysis of enantiomer AAs. The chiral MOF of d-Co0.75Zn0.25-MOF-74 is designed and prepared by modifying the Co0.75Zn0.25-MOF-74 with d-tartaric acid. The developed chiral bimetallic MOF can not only offer the chiral recognize sites but also act as the catalyst in the cyclic luminol-H2O2 reaction. Moreover, a distinguishable CCL signal can be obtained on enantiomer AAs via the luminol-H2O2 reaction with the control of d-Co0.75Zn0.25-MOF-74. The amplified difference of enantiomer AAs can be quantified by the decay coefficient (k-values) which are calculated from the exponential decay fitting of their obtained CCL signals. According to simulation results, the selective recognition of 19 pairs of AAs is controlled by the pore size of the MOF-74 and their hydrogen-bond interaction with d-tartaric acid on the chiral MOF. Furthermore, the k-values can also be used to estimate the change of chiral AAs in complex samples. Consequently, this chiral MOF-controlled CCL reaction is applied to differentiate enantiomer AAs involved in the quality monitoring of dairy products and auxiliary diagnosis, which provides a new approach for chiral studies and their potential applications.

RSEDM: A New Rotational-Scan Exponential Decay Model for Extracting the Surface Urban Heat Island Footprint

Surface urban heat islands are widely focused on due to their close relationship with a series of environmental issues. Obtaining a precise footprint is an important prerequisite for heat island research. However, the land surface temperature curves used for calculating footprint are affected by factors such as the complexity of land-use types, thereby affecting the accuracy of footprint. Therefore, the rotational-scan exponential decay model is developed in this paper, which first takes the gravity center of an urban area as the origin of polar coordinates, specifies due north as the starting direction, and rotationally scans the suburbs that are within 20 km outside urban areas in a clockwise direction at an angle of 1°. The eligible suburbs are screened out according to the built-up area rate, water body rate, and merge tolerance. Then, exponential decay fitting of the temperature curve is performed to obtain the extension distance of the heat island and the background temperature, which are used to determine the final footprint. Based on the method, the footprints of 15 cities were calculated and compared with those of the traditional method. The results show that: (1) this method could effectively eliminate the influence of a large number of contiguous built-up areas and water bodies in the suburbs on the footprint calculation, thus greatly improving the accuracy of the temperature curve and footprint. (2) Three of four cities had the largest footprint boundary in spring. All four cities had the strongest heat island intensity in summer and the smallest footprint boundary and intensity in winter. (3) Coupling effect would aggravate the negative impact of heat islands in the suburbs and threaten the suburban environment. As a state-of-the-art method, it can enhance the calculation accuracy and precisely reflect the spatial pattern of footprint, which is of great significance for the sustainable development of cities.

Stress relaxation behavior of left ventricular myocardium in mice

BackgroundMyocardial tissues are known to exhibit viscoelastic behavior, i.e., the myocardial wall stress is gradually decaying when stretched at a constant level, referred to as stress relaxation behavior. The study of this behavior becomes important in structural heart diseases, where both passive and active relaxation behaviors of the myocardium may alter. As myocardial tissues display a complex, 3D micro‐architecture, the anisotropy of stress relaxation remains understudied. Our objective in this study was to investigate the anisotropy of (passive) stress relaxation behavior of the left ventricular (LV) myocardium in healthy small animals.MethodsWe used biaxial stress relaxation tests in wild‐type murine specimens (n=2). Full‐thickness myocardium LV free wall (LVFW) specimens were isolated from the mouse hearts (Fig. 1a), with the slab edges being aligned with the longitudinal (apex‐to‐outflow‐tract), circumferential, and radial directions of the LV. The specimens were mounted in a biaxial mechanical testing machine along the circumferential and longitudinal directions. The specimens were stretched in three different loading protocols with circumferential‐to‐longitudinal strain ratios of 30:30, 15:30, and 30:15%. The samples were loaded to the peak strain at a rate of 0.01 s‐1 and held at this stretch for 10 minutes to allow the relaxation. The time‐varying stress was recorded. We used an exponential decay fit to estimate the stress relaxation time constants in both directions.ResultsStress relaxation time constants showed noticeable differences between multiple loading ratios with equibiaxial loading (30:30) having the largest relaxation time constant followed by the circumferential stress in the 30:15 ratio (Fig. 1b). The larger strains led to larger stress relaxation constants (Fig. 1b‐c) indicating a strain‐dependent viscoelastic behavior. The quasi‐static equibiaxial loading of the same specimens resulted in a nearly isotropic behavior (not shown here), exhibiting insignificant contrast between the stresses in the circumferential and longitudinal directions. Interestingly, the contrast in the relaxation behavior between the circumferential and longitudinal directions were similarly insignificant (Fig. 1b). Non‐equibiaxial loadings (15:30 and 13:50) showed significantly faster relaxation for the direction with smaller strains (Fig. 1b).ConclusionsMyocardial tissue viscoelasticity is an important behavior contributing to both diastolic and systolic cardiac function, which remains understudied, especially in case of structural heart diseases associated with impaired relaxation in the LV. Our study suggests that stress relaxation behavior is prominent in the LV myocardium and may exhibit different relaxation behavior depending on strain magnitudes and strain ratios along different directions. The level of anisotropy in stress relaxation was found to be similar to the level of anisotropy in the tissue quasi‐static behavior. These results serve to motivate further studies to fully characterize the viscoelastic behavior of LV myocardium and its contribution to the LV relaxation and filling in murine models of LV diseases.

On the Relationship Between EB-3 Profiles and Microtubules Growth in Cultured Cells.

Microtubules are dynamic structures undergoing rapid growth and shrinkage in living cells and in vitro. The growth of microtubules in vitro was analyzed with subpixel precision (Maurer et al., Current Biology, 2014, 24 (4), 372–384); however, to what extent these results could be applied for microtubules growing in vivo remains largely unknown. Particularly, the question is whether microtubule growth velocity in cells could be sufficiently approximated by a Gaussian distribution or its variability requires a more sophisticated description? Addressing this question, we used time-lapse microscopy and mathematical modeling, and we analyzed EB-3 comets forming on microtubules of cultured cells with subpixel precision. Parameters of comets (shape, form, and velocity) were used as topological characteristics of 3D voxel objects. Using regression analysis, we determined the real positions of the microtubule tips in time-lapse sequences. By exponential decay fitting of the restored comet intensity profile, we found that in vivo EB-3 rapidly exchanges on growing microtubule ends with a decoration time ∼ 2 s. We next developed the model showing that the best correlation between comet length and microtubule end growth velocity is at time intervals close to the decoration time. In the cells, EB comet length positively correlates with microtubule growth velocity in preceding time intervals, while demonstrating no correlation in subsequent time intervals. Correlation between comet length and instantaneous growth velocity of microtubules remains under nocodazole treatment when mean values of both parameters decrease. Our data show that the growth of microtubules in living cells is well-approximated by a constant velocity with large stochastic fluctuations.

P‐GeSe/n‐ReS2 Heterojunction Rectifier Exhibiting A Fast Photoresponse with Ultra‐High Frequency‐Switching Applications

AbstractThe most emerging 2D‐materials‐based heterostructures are considered promising candidates because of their multifunctional logic applications for electric and optoelectronic devices. Here, a high gate tunable rectification in van der Waals heterostructure composed of n‐type rhenium disulfide (n‐ReS2) and p‐type germanium selenide (p‐GeSe), using pure Ohmic contacts, is reported. The large rectification ratio (RR) deprived of any Schottky contribution is tuned up to 4 × 105 because of the sharp interface of p‐GeSe and n‐ReS2. The sheet‐thickness effect over the rectification is also observed in the p‐GeSe/n‐ReS2 heterostructure as well. The profound photovoltaic measurements under lights of different power intensities depict a high photo responsivity of 3.9 × 103 A W−1 with an external quantum efficiency of 87% and specific detectivity (D* = 1.5 × 1012). The fast growth (16.6 µs) and decay times (12.3 µs) are extracted by the exponential rise and decay fitting. Moreover, practical applications of the p‐GeSe/n‐ReS2 heterostructure devices are exhibited by observing inverter behavior and high‐frequency switching operations, which is also the breakthrough of this research. Fabrication of such smart devices based on transition metal dichalcogenides (TMDs) van der Waals heterostructures may enhance the energy harvesting as well as the multifunctional logic switches.

Single ion qubit with estimated coherence time exceeding one hour

Realizing a long coherence time quantum memory is a major challenge of current quantum technology. Until now, the longest coherence-time of a single qubit was reported as 660 s in a single 171Yb+ ion-qubit through the technical developments of sympathetic cooling and dynamical decoupling pulses, which addressed heating-induced detection inefficiency and magnetic field fluctuations. However, it was not clear what prohibited further enhancement. Here, we identify and suppress the limiting factors, which are the remaining magnetic-field fluctuations, frequency instability and leakage of the microwave reference-oscillator. Then, we observe the coherence time of around 5500 s for the 171Yb+ ion-qubit, which is the time constant of the exponential decay fit from the measurements up to 960 s. We also systematically study the decoherence process of the quantum memory by using quantum process tomography and analyze the results by applying recently developed resource theories of quantum memory and coherence. Our experimental demonstration will accelerate practical applications of quantum memories for various quantum information processing, especially in the noisy-intermediate-scale quantum regime.

Biomass crops as a soil amendment in cultivated histosols: Can we reach carbon equilibrium?

AbstractPeatlands are known to perform essential economical, societal and regulating functions. Once they are drained to provide optimal crop growth conditions, however, a series of degradation processes is generated. Wind and water erosion, subsidence and soil organic matter oxidation are the main causes of degradation observed in cultivated histosols. This study evaluated the decomposition dynamics and chemical changes of three biomass crops during an in‐situ incubation in a cultivated histosol. The decomposition dynamics characterized in the field study were then used in a simulation to determine if sustainability could be reached by using biomass crops as a soil amendment. The results showed that an exponential decay fitting curve best represented the weight loss of sorghum [Sorghum bicolor (L.) Moench] in the in‐situ bags over time, while a logistic fitting curve best represented that of miscanthus (Miscanthus X giganteus) and willow (Salix miyabeana). The quality of the crop determined the initial and overall decomposition dynamics observed. The loss of carbon from the crushed biomass crop was much more important in sorghum than in miscanthus and willow. The long‐term simulation of histosol amendment revealed that using miscanthus and willow at input rates of 7.5 and 10 T of carbon per year, respectively, would be sufficient to ensure sustainability. Improving knowledge on carbon loss in cultivated histosols as related to soil and crop management would help in developing a soil amendment program at the farm scale. In addition, more knowledge is needed to determine the impact of long‐term and successive amendment with biomass crops on the physical and biochemical properties of histosols.

Release of Pharmaceutical Peptides in an Aggregated State: Using Fibrillar Polymorphism to Modulate Release Levels

Traditional approaches to achieve sustained delivery of pharmaceutical peptides traditionally use co-excipients (e.g., microspheres and hydrogels). Here, we investigate the release of an amyloidogenic glucagon analogue (3474) from an aggregated state and the influence of surfactants on this process. The formulation of peptide 3474 in dodecyl maltoside (DDM), rhamnolipid (RL), and sophorolipid (SL) led to faster fibrillation. When the aggregates were subjected to multiple cycles of release by repeated resuspension in fresh buffer, the kinetics of the release of soluble peptide 3474 from different surfactant aggregates all followed a simple exponential decay fit, with half-lives of 5–18 min and relatively constant levels of release in each cycle. However, different amounts of peptide are released from different aggregates, ranging from 0.015 mg/mL (3475-buffer) up to 0.03 mg/mL (3474-DDM), with 3474-buffer and 3474-RL in between. In addition to higher release levels, 3474-DDM aggregates showed a different amyloid FTIR structure, compared to 3474-RL and 3474-SL aggregates and a faster rate of degradation by proteinase K. This demonstrates that the stability of organized peptide aggregates can be modulated to achieve differences in release of soluble peptides, thus coupling aggregate polymorphism to differential release profiles. We achieved aggregate polymorphism by the addition of different surfactants, but polymorphism may also be reached through other approaches, including different excipients as well as changes in pH and salinity, providing a versatile handle to control release profiles.

Localized Surface Plasmon on 6H SiC with Ag Nanoparticles

Silver (Ag) nanoparticles (NPs) were deposited on the surface of bulk Nitrogen-Boron co-doped 6H silicon carbide (SiC), and the Ag NPs were observed to induce localized surface plasmons (LSP) resonances on the SiC substrate, which was expected to improve the internal quantum efficiency (IQE) of the emissions of the donor-acceptor pairs of the SiC substrate. Room-temperature measurements of photoluminescence (PL), transmittance and time-resolved photoluminescence (TRPL) were applied to characterize the LSP resonances. Through the finite-difference time-domain (FDTD) simulation of the LSP resonance of an Ag nanoparticle on the SiC substrate, it is predicted that when the diameter of the cross section on the xy plane of the Ag nanoparticle is greater than 225 nm, the LSP starts to enhance the PL intensity. With implementation of a 3rd order exponential decay fitting model to the TRPL results, it is found that the average minority carrier lifetime of the SiC substrate decreased.

Detection of bubble nucleation event in superheated drop detector by the pressure sensor

Superheated drop detector consisting of drops of superheated liquid suspended in polymer or gel matrix is of great demand, mainly because of its insensitivity to s-particles and ?-rays and also because of the low cost. The bubble nucleation event is detected by measuring the acoustic shock wave released during the nucleation process. The present work demonstrates the detection of bubble nucleation events by using the pressure sensor. The associated circuits for the measurement are described in this article. The detection of events is verified by measuring the events with the acoustic sensor. The measurement was done using drops of various sizes to study the effect of the size of the drop on the pressure recovery time. Probability of detection of events has increased for larger size of the superheated drops and lesser volume of air in contact with the gel matrix. The exponential decay fitting to the pressure sensor signals shows the dead time for pressure recovery of such a drop detector to be a few microseconds.

A Study on the Change of Positive Vergence and Accommodative power according to Illumination

Purpose: The purpose of this study is to investigate changes of positive vergence and accommodative power with illumination. Methods: 49 subjects(mean age:24.51±2.82) having no systemic and ocular disease were recruited. Illuminance environment is going to use the light meter ((LX-101, Lutron, USA) and dimmers to change the light intensity from 10 lux to 1000 lux measured the amplitude of accommodation and far/near positive vergence. Results: Amplitude of accommodation was lowest to 8.51 D with 10 lux and the highest to 9.12 D with 800 lux. As the illuminance increases, the exponential decay fit(y=9.09-0.62e-) was maintained while also increasing amplitude of accommodation. Break point of distance positive vergence was higher by 20.81 △ at low illuminance of 10 lux, near positive vergence was higher by 21.42 △ at low illuminance of 10 lux. The exponential decay fit of Distance/near positive vergence were y=17.08+4.66e- and y=20.93+0.63e- , respectively. Conclusions: As the illuminance increases while amplitude of accommodation is increasing, Distance/near positive vergence was increase in low light, while temporarily reduced while increasing illuminance showed a pattern that changes less.

Comprehensive Hemodynamic Analysis of Arteriolar Networks in the Rat Gluteus Maximus Muscle

IntroductionTheoretical blood flow models enable comprehensive analysis of blood flow, pressure, resistance, and hematocrit distribution within microvascular networks. However, the validity of data produced by such models is dependent on the detail of its experimentally derived inputs. Currently, many theoretical models of skeletal muscle hemodynamics are limited to incorporating experimental inputs from small network segments or trees, or from non‐locomotive tissues such as the mesentery. Thus, the objective of this study was to utilize recently collected experimental (geometric and topological) data from complete arteriolar networks of locomotive skeletal muscle as inputs for our computational blood flow model. Using outputs from theoretical simulations, we evaluated inter‐network hemodynamic variability in an effort to describe the level of functional homology among skeletal muscle arteriolar networks.MethodsThe rat GM provides the ideal experimental model to study locomotive skeletal muscle. Its planar geometry and uniform thinness enable access (within a single focal plane) to its entire microcirculation for microscopic imaging and perturbation. Using intravital videomicroscopy, the GM (n=4) was scanned under baseline conditions and photomontages were compiled (~400 images per network). Photomontages were registered to a MATLAB x–y coordinate system and scaled digital networks were generated. Approximately 1500 discrete nodes were used to mathematically model each network, with an average length of approximately 100 μm between each node, resulting in 179 to 239 vessel segments per network. A previously established two‐phase blood flow model (MATLAB) was used to simulate and assess the hemodynamic properties of each arteriolar network including heterogeneity within each network and variability between networks.ResultsBlood flow rate in each vessel segment decayed exponentially with increasing (1A to 9A) arteriolar order for each network (Exponential Decay fit: R2 0.71 to 0.88). Additionally, the coefficients of variation (a measure of blood flow distribution) at each order ranged from 30.24% to 86.79%. Log‐log plots between blood flow and arteriolar diameter showed a strong correlation for each network (Linear Regression, R2 0.65 to 0.86) with similar slopes of regression lines (3.08 to 3.81).ConclusionSimulation results show strong homology in blood flow properties between all the networks considered. Other hemodynamic properties such as RBC flow and hematocrit, as well as overall resistance, are now being analyzed with respect to both arteriolar order and diameter. This analysis allows detailed comparison of the hemodynamic properties of the different arteriolar networks studied, including the extent to which observed topological and geometric homologies result in similar hemodynamic outcomes.Support or Funding InformationNSERC

Temporal binning of time-correlated single photon counting data improves exponential decay fits and imaging speed.

Time-correlated single photon counting (TCSPC) enables acquisition of fluorescence lifetime decays with high temporal resolution within the fluorescence decay. However, many thousands of photons per pixel are required for accurate lifetime decay curve representation, instrument response deconvolution, and lifetime estimation, particularly for two-component lifetimes. TCSPC imaging speed is inherently limited due to the single photon per laser pulse nature and low fluorescence event efficiencies (<10%) required to reduce bias towards short lifetimes. Here, simulated fluorescence lifetime decays are analyzed by SPCImage and SLIM Curve software to determine the limiting lifetime parameters and photon requirements of fluorescence lifetime decays that can be accurately fit. Data analysis techniques to improve fitting accuracy for low photon count data were evaluated. Temporal binning of the decays from 256 time bins to 42 time bins significantly (p<0.0001) improved fit accuracy in SPCImage and enabled accurate fits with low photon counts (as low as 700 photons/decay), a 6-fold reduction in required photons and therefore improvement in imaging speed. Additionally, reducing the number of free parameters in the fitting algorithm by fixing the lifetimes to known values significantly reduced the lifetime component error from 27.3% to 3.2% in SPCImage (p<0.0001) and from 50.6% to 4.2% in SLIM Curve (p<0.0001). Analysis of nicotinamide adenine dinucleotide-lactate dehydrogenase (NADH-LDH) solutions confirmed temporal binning of TCSPC data and a reduced number of free parameters improves exponential decay fit accuracy in SPCImage. Altogether, temporal binning (in SPCImage) and reduced free parameters are data analysis techniques that enable accurate lifetime estimation from low photon count data and enable TCSPC imaging speeds up to 6x and 300x faster, respectively, than traditional TCSPC analysis.

Elution dynamics of M13 bacteriophage bound to streptavidin immobilized in a microfluidic channel

Microfluidic biopanning can reduce a sample size and improve the reproducibility of biopanning. However, there is no practical guideline for optimal experimental conditions to identify high affinity peptides, including incubation and washing times and washing and elution flow rates. Here we investigated the elution dynamics of M13 phage displaying a well-known streptavidin-binding peptide motif, histidine-proline-glutamine (HPQ), to streptavidin immobilized in a polydimethylsiloxane microfluidic channel via a biotin-polyethylene glycol linker. The phages bound to streptavidin were eluted using an acidic buffer, which weakens the molecular interactions of HPQ and streptavidin. Various washing flow rates were examined to determine the effects of drag forces on the elution of phages, and the total force per phage combined with the drag force was calculated. The critical washing drag force and washing time were 5.9×10-8 dyne and 1.1 min, respectively, as obtained by fitting the data using a sigmoidal function. The dissociation rate constant of HPQ-displaying phage (2.0×10-2 min-1) was also obtained from the double exponential decay fitting. Our work provides a practically useful approach to the optimization of experimental parameters for the design of a microfluidic biopanning platform.

SU‐E‐T‐78: A Study of Dose Falloff Gradient in RapidArc Planning of Lung SBRT

Purpose:Rapid dose falloff beyond PTV is an important criterion for normal tissue sparing in SBRT. RTOG protocols use D2cm and R50% for plan quality evaluation. This study is aimed at analyzing the dose falloff gradient beyond the PTV extending into normal tissue structures and to ascertain the impact of PTV geometry and location on the dose falloff gradient in RapidArc planning of lung SBRTMethods:In this retrospective study, we analyzed 39 clinical RapidArc lung SBRT treatment plans that met RTOG‐0915 criteria. Planning was done on Eclipse 8.9 for delivery on either Novalis NTx or TrueBeam STx equipped with HD MLCs. PTV volumes ranged between 5.3 and 113 cc (2.2 to 6 cm sphere equivalent diameter respectively) and their geographic locations were distributed in both lungs. 6X, 6X‐FFF, 10X, and 10X‐FFF energies were used for planning. All of these SBRT plans were planned using either 2 or 3 full or hemi arcs, with moderate couch kicks. Dose falloff gradients were obtained by generating 7 concentric 5 mm rings beyond PTV surface. Mean dose in each ring is used to evaluate percentage dose falloff gradient as a function of distance from the PTV surface.Results:The mean percentage dose falloff beyond PTV surface in all plans followed an exponential decay and the data was modeled with double exponential decay fit. Photon energy selection in the plan had a minimal impact on the mean percentage dose fall off beyond PTV surface.Conclusion:Dose falloff beyond PTV surface as a function of distance can be ascertained by the use of the double exponential decay fit coefficients in RapidArc planning of lung SBRT. This will help also in plan quality evaluation in addition to D2cm and R50% defined by RTOG.