Fast Decay Research Articles

Water-in-Salt: Fast Dynamics, Structure, Thermodynamics, and Bulk Properties.

We present concentration-dependent dynamics of highly concentrated LiBr solutions and LiCl temperature-dependent dynamics for two high concentrations and compare the results to those of prior LiCl concentration-dependent data. The dynamical data are obtained using ultrafast optical heterodyne-detected optical Kerr effect (OHD-OKE). The OHD-OKE decays are composed of two pairs of biexponentials, i.e., tetra-exponentials. The fastest decay (t1) is the same as pure water's at all concentrations within error, while the second component (t2) slows slightly with concentration. The slower components (t3 and t4), not present in pure water, slow substantially, and their contributions to the decays increase significantly with increasing concentration, similar to LiCl solutions. Simulations of LiCl solutions from the literature show that the slow components arise from large ion/water clusters, while the fast components are from ion/water structures that are not part of large clusters. Temperature-dependent studies (15-95 °C) of two high LiCl concentrations show that decreasing the temperature is equivalent to increasing the room temperature concentration. The LiBr and LiCl concentration dependences and the two LiCl concentrations' temperature dependences all have bulk viscosities that are linearly dependent on τcslow, the correlation time of the slow dynamics (weighted averages of t3 and t4). Remarkably, all four viscosity vs 1/τCslow plots fall on the same line. Application of transition state theory to the temperature-dependent data yields the activation enthalpies and entropies for the dynamics of the large ion/water clusters, which underpin the bulk viscosity.

Temperature dependence of photo- and radio-luminescence and scintillation properties of Lu2YAl2.5Ga2.5O12:Ce,Mg multicomponent garnet crystals

Luminescence and scintillation properties of Lu2YAl2.5Ga2.5O12:Ce,Mg (0.02, 0.05 %) garnet crystals grown by the micro-pulling down method were investigated. The onset temperature for luminescence quenching at ∼365 K is determined from the temperature dependence of photoluminescence decay time. At room temperature, the Mg (0.05 %) sample exhibits high integral scintillation efficiency of ∼445 % of BGO crystal, light yield value of 23,500 photons/MeV, and fast scintillation decay times of 20 ns (15 %) + 54 ns (85 %). The higher radioluminescence intensity of the Mg (0.05 %) sample correlates with an appearance of its lower themally-stimulated luminescence intensity in 77–500 K range.

Bound Ca2+ moves faster and farther from single open channels than free Ca2.

A concept of Ca2+ nanodomains established in the cytoplasm after opening single-calcium channels helps mechanistically understand the physiological mechanisms of Ca2+ signaling. It predicts standing gradients of cytoplasmic free Ca2+ around single channels in the plasma membrane. The fate of bound Ca2+ attracted much less attention. This study aimed to examine the profiles of Ca2+ bound to low-mobility buffers such as bulky Ca2+-binding proteins. The solution of non-linear PDEs for an immobile buffer predicts fast decay of free [Ca2+] from the channel lumen and the traveling wave for bound Ca2+. For low-mobility buffers like calmodulin, the calculated profiles of free and bound Ca2+ are similar. Theoretical predictions are tested by imaging 1D profiles of Ca2+ bound to low-mobility fluo-4-dextran. The traveling waves of bound Ca2+ are observed that develop during the opening of single channels. The findings tempt to propose that Ca2+ signaling may not be solely related by the absolute free [Ca2+] at the sensor location, which is extremely localized, but determined by the time when a wave of bound Ca2+ reaches a threshold needed for sensor activation.

The dependence of thermoluminescence and optically stimulated luminescence properties of LiMgPO4: Tb,Sm,B on maximum heating temperatures

The dependence of thermoluminescence (TL) and optically stimulated luminescence (OSL) properties of LiMgPO4:Tb,Sm,B samples prepared by the high-temperature solid-state method on maximum heating temperatures was investigated for the first time. The TL glow curves showed the ratio of peak 3 to peak 2 increased with the increase of maximum heating temperature. The influence of OSL on maximum heating temperatures showed that the sensitivity of OSL reached the maximum at the maximum heating temperature of 1000°C, which is 11.6 times higher than that of 800 °C. The relative standard deviation of the repeatability is less than 1.5% regardless of the maximum heating temperature. The minimum measurable dose (MMD) could be significantly improved by optimizing OSL parameters, such as maximum heating temperature and readout time. The MMD as low as 0.31 µGy has been achieved. The residual OSL is up to 92.3% after irradiation for 24 h. LiMgPO4:Tb,Sm,B is highly sensitive to the maximum heating temperature. Considering fast decay time, high OSL sensitivity, good repeatability, low MMD and little fading, it is recommended that the maximum heating temperature of LiMgPO4:Tb,Sm,B is 1000°C. LiMgPO4:Tb,Sm,B has great potential for daily personal and environmental cumulative dose monitoring.

Strongly Luminescent Tetradentate Palladium(II)‐TADF Emitters. Blue TADF And TADF‐Sensitized OLEDs with External Quantum Efficiencies Over 23%

AbstractDue to the low‐lying Pd(4d)‐orbitals, luminescent palladium(II) complexes usually show 3IL phosphorescence (IL = intraligand) with excited state lifetimes in the range of hundreds of microseconds, which limits their application in blue organic light‐emitting diodes (OLEDs). Here, a molecular design strategy for the development of strongly luminescent Pd(II)‐based thermally activated delayed fluorescence (TADF) emitters with fast radiative decay rate constants and reverse intersystem crossing rate (kRISC) constants is presented. The synthesized tetradentate [Pd(N*C*C^N)] TADF emitters show sky‐blue to yellow (λmax = 484–565 nm) emission with excited state lifetimes in the range of 0.9−8.7 µs and high photoluminescence quantum yield of up to 77% in CH2Cl2 solution. In 5 wt.% 2,8‐bis(diphenylphosphoryl)dibenzo[b,d]furan (PPF) thin films, these [Pd(N*C*C^N)] TADF complexes display blue to sky‐blue (476−496 nm) emission with quantum yields close to unity. Variable‐temperature emission lifetime measurements, femtosecond time‐resolved spectroscopy, and density functional theory (DFT) and time‐dependent DFT (TDDFT) calculations together reveal ultrafast kRISC rate constants of these [Pd(N*C*C^N)] TADF emitters. Using these Pd(II)‐TADF emitters as dopants, sky‐blue TADF and blue TADF‐sensitized OLEDs with small efficiency roll‐offs achieved high maximum external quantum efficiencies (EQEs) of 24.8% and 23.1%, respectively.

Effect of Molecular Dynamics and Internal Water Contact on the Photophysical Properties of Red pH-Sensitive Proteins.

The pH dependence of the absorption and (time-resolved) fluorescence of two red-shifted fluorescent proteins, mCardinal and mNeptune, was investigated. Decay-associated spectra were measured following fluorescence excitation at 470 nm in PBS buffer with a pH that ranged from 5.5 to 8.0. The fluorescence of both proteins shows two different decay components. mCardinal exhibits an increase in the long-lived fluorescence component with acidification from 1.34 ns at pH 8.0 to 1.62 ns at pH 5.5. An additional fast decay component with 0.64 ns at pH 8.0 up to 1.1 ns at pH 5.5 was found to be blue-shifted compared to the long-lived component. The fluorescence lifetime of mNeptune is insensitive to pH. DAS of mCardinal were simulated assuming a coupled two-level system to describe the 1S state of the chromophore within two different conformations of the protein. MD simulations were conducted to correlate the experimentally observed pH-induced change in the lifetime in mCardinal with its molecular properties. While the chromophores of both protein variants are stabilized by the same number of hydrogen bonds, it was found that the chromophore in mCardinal exhibits more water contacts compared to mNeptune. In mCardinal, interaction between the chromophore and Glu-145 is reduced as compared to mNeptune, but interaction with Thr-147 which is Ser-147 in mNeptune is stronger in mCardinal. Therefore, the dynamics of the excited-state proton transfer (ESPT) might be different in mCardinal and mNeptune. The pH dependency of ESPT is suggested as a key mechanism for pH sensitivity.

Long-Lived and Bright Biexcitons in Quantum Dots with Parabolic Band Potentials.

Multiple exciton physics in semiconductor nanocrystals play an important role in optoelectronic devices. This work investigates radially alloyed CdZnSe/CdS nanocrystals with suppressed Auger recombination due to the spatial separation of carriers, which also underpins their performance in optical gain and scintillation experiments. Due to suppressed Auger recombination, the biexciton lifetime is greater than 10 ns, much longer than most nanocrystals. The samples show optical gain, amplified spontaneous emission, and lasing at thresholds <2 excitons per particle. They also show broad gain bandwidth (>500 meV) encompassing 4 amplified spontaneous emission bands. Similarly enabled by slowed multiple exciton relaxation, the samples display strong performance in scintillating films under X-ray illumination. The CdZnSe/CdS samples have fast radioluminescence rise (<80 ps) and decay times (<5 ns), light yields up to 6700 photons·MeV-1, and the demonstrated capacity for incorporation into large area films for scintillation imaging.

Calcium-based metal–organic framework as an optimized anode material for Li-ion batteries

Metal–organic frameworks (MOFs) as attracting electrode materials for lithium-ion batteries (LIBs) suffer seriously from structural instability, leading to the fast decay of capacity. Introducing insolvable metal ion bonding strongly with functional groups into MOF may effectively stabilize the electrode and improve the Li+ ion reaction stability during the electrochemical processes. In this work, a calcium-based metal–organic framework (Ca2PMA) is synthesized by a cation exchange method and explored as an anode material for LIBs. Ca2PMA exhibits a large reversible capacity of 673.9 mAh g−1 (100 mA g−1) as well as good cycle performance. Upon activation from the first cycle to the 320th cycle at 500 mA g−1, an extremely large reversible capacity of ∼360 mAh g−1 is achieved and there is almost no capacity fading until the 800th cycle. During the activation stage, the crystalline structure of Ca2PMA deteriorates quickly to be amorphous, while the capacity continuously increases. A 14-electron redox chemistry is proposed for the Ca2PMA monomer, and the high cycle stability is attributed to the insolvable Ca2+ stabilized functional groups.

Pyramidal island for enhance response in ZnO/Cu2O heterojunction self-powered photodetector

Self-powered photodetectors (PDs) with high performance are essential for applications in mobile portable electronics, communications, and sensing. However, the limited light absorption of the traditional planar heterojunction interface seriously restricts the commercial application of photodetectors. In this study, a new type PD with pyramidal island-like ZnO/Cu2O heterojunction interface was designed and prepared by electrochemical deposition and radio frequency (RF) magnetron sputtering technology using the inherent octahedral structure of Cu2O, and its unique pyramid island interface was conducive to improving the light utilization efficiency and photoelectric performance of the detector. Under zero bias conditions, the responsivities of 0.32 and 0.09 A W−1 were obtained under 380 nm and 550 nm illumination, respectively. And the PD exhibit fast rise and decay times of 0.163 and 0.179 s. The maximum external quantum efficiency reaches 107.18 %. The results demonstrate that our highly efficient and fast response self-powered PD is expected to be a candidate for next generation ultraviolet (UV) -visible photosensing applications.

Two-Color Amplified Spontaneous Emission from Auger-Suppressed Quantum Dots in Liquids.

Colloidal quantum-dot (QD) lasing is normally achieved in close-packed solid-state films, as a high QD volume fraction is required for stimulated emission to outcompete fast Auger decay of optical-gain-active multiexciton states. Here a new type of liquid optical-gain medium is demonstrated, in which compact compositionally-graded QDs (ccg-QDs) that feature strong suppression of Auger decay are liquefied using a small amount of solvent. Transient absorption measurements of ccg-QD liquid suspensions reveal broad-band optical gain spanning a wide spectral range from 560 (green) to 675nm (red). The gain magnitude is sufficient to realize a two-color amplified spontaneous emission (ASE) at 637 and 594nm due to the band-edge (1S) and the excited-state (1P) transition, respectively. Importantly, the ASE regime is achieved using quasicontinuous excitation with nanosecond pulses. Furthermore, the ASE is highly stable under prolonged excitation, which stands in contrast to traditional dyes that exhibit strong degradation under identical excitation conditions. These observations point toward a considerable potential of high-density ccg-QD suspensions as liquid, dye-like optical gain media that feature readily achievable spectral tunability and stable operation under intense photoexcitation.

Construction of Co1-xS Nanoparticles Embedding in N-Doped Amorphous Carbon@Graphene with Enhanced Li-Ion Storage.

Cobalt sulfide is deemed a promising anode material, owing to its high theoretical capacity (630mAhg-1). Due to its low conductivity, fast energy decay, and the huge volume change during the lithiation process limits its practical application. In this work, a simple and large-scale method are developed to prepare Co1-xS nanoparticles embedding in N-doped carbon/graphene (CSCG). At a current density of 0.2C, the reversible discharge capacity of CSCG maintains 937mAhg-1 after 200 cycles. The discharge capacity of CSCG maintains at 596mAhg-1 after 500 cycles at the high current density of 2.0C. The excellent performance of CSCG is due to its unique structural features. The addition of rGO buffered volume changes while preventing Co1-xS from crushing/aggregating during the cycle, resulting in multiplier charge-discharge and long cycle life. The N-doped carbon provides a simple and easy way to achieve excellent performance in practical applications. Combined with density functional theory calculation, the presence of Co-vacancies(Co1-x) increases more active site. Moreover, N-doping carbon is beneficial to the improve adsorption energy. This work presents a simple and effective structural engineering strategy and also provides a new idea to improve the performance of Li-ion batteries.

Measuring the Contractile Kinetics of Isolated Myofibrils from Human-Induced Pluripotent Stem Cell Derived Cardiomyocyte (hiPSC-CM) Models of Cardiomyopathy.

Isolated myofibrils provide biomechanical data at the contractile organelle level that are independent of cellular calcium handling and signaling pathways. These myofibrils can be harvested from animal tissue, human muscle biopsies, or stem cell-derived striated muscle. Here we present our myofibril isolation and rapid solution switching protocols, which allow for precise measurements of activation (kinetics and tension generation) and a biphasic relaxation relationship (initial slow isometric relaxation followed by a fast exponential decay in tension). This experiment is generated on a custom-built myofibril apparatus utilizing a two-photodiode array to detect micron level deflection of our forged glass tip force transducers. A complete activation/relaxation curve can be produced from a single myofibril in under 30minutes.

R&D of glass scintillator for nuclear radiation detection

In 2021, the Institute of High Energy Physics proposed a design of glass scintillator coupled with SiPM as a new solution for the next generation calorimeter, to explore the application of glass scintillators in high energy physics and nuclear radiation detection. The Large Area Glass Scintillator Collaboration Group was established to research and develop a glass scintillator with high density, high light yields and fast decay time. Through continuous optimization, the glasses have excellent scintillation performance with a light yield of 1000 ph/MeV and a density of 6 g/cm3. Moreover, the neutron response of the glasses was investigated, and different high-energy particles can be distinguished by signal amplitude. In addition, the radiation resistance of different glasses was tested under proton beam. All the glasses appeared opaque and produced a high radioactive background, because Gd element interacts with proton to produce radionuclides with high activity and long half-life.

Weighted Laterally Constrained Inversion of Airborne Transient Electromagnetic Data with IP Effects

Due to the induced polarization (IP) effects, abnormal fast decay and sign reversals are often observed in the field airborne transient electromagnetic (ATEM) responses, this phenomenon can well be explained by introducing the four-parameter Cole-Cole resistivity model. However, the introduction of multiple parameters makes the non-uniqueness of inversion more serious. To improve this problem, a weighted 1D laterally constrained inversion is proposed to recover the four IP parameters and thickness via adding different weighted factors chosen by lateral constraint conditions, in this paper, a synthetic polarization model is developed and 1D forward modeling with synthetic natural noise is conducted to imitate the field response. The proposed inversion is employed on the synthetic data and the results demonstrate that the method can improve the inversion stability and obtain more reliable result.

Cleaning effects due to shape oscillation of bubbles over a rigid boundary

Recent experiments have revealed the interesting cleaning effects that take place due to the shape mode oscillation of bubbles over a rigid boundary. While a microbubble was undertaking shape oscillation moving over a bacterial biofilm, it removed the contaminants from the boundary and created a clean path through the biofilm. This demonstrated much higher cleaning efficiency than that associated with the volume oscillation of cavitation bubbles; however, the mechanism is unknown. Here, we study this phenomenon using the boundary integral method with the viscous effects modeled using the viscous potential flow theory and the compressible effects using the weakly compressible theory. The viscous stress at the rigid boundary is approximated using the boundary layer theory. We observed that the natural frequencies of shape mode oscillation decrease significantly due to the presence of the boundary. The shear stress at the boundary due to the shape oscillation of a nearby bubble is at least 20 times higher than that due to volume oscillation with the same energy and is significant only within the area directly beneath the bubble. This is explained by the notably faster decay for higher shape modes of the kinetic energy in the fluid as the distance to the center of the bubble r increases with the induced velocity of mode k decaying at a rate of O(r−(k+2)) away from the bubble. These results achieve excellent agreement with the intriguing cleaning effects first observed in the experiment and explain the mechanism behind this new highly efficient method of cleaning.

Tensor characteristics of forward Brillouin sensors in bare and coated fibers

Forward Brillouin scattering fiber sensors can detect and analyze media outside the cladding of standard fibers, where guided light does not reach. Nearly all such sensors reported to-date have relied on the radially symmetric guided acoustic modes of the fiber. Wave motion in these modes is strictly dilatational. However, forward Brillouin scattering also takes place through torsional–radial guided acoustic modes of the fiber. Torsional–radial modes exhibit more complex tensor characteristics, and they consist of both dilatational and shear wave contributions. In this work, we show that forward Brillouin sensing through torsional–radial acoustic modes is qualitatively different from processes based on the radial ones. While dilatational wave components may dissipate toward liquids outside the fiber cladding, shear waves do not. Consequently, the effect of outside liquids varies among torsional–radial modes. Those modes that are dominated by their dilatational components undergo faster decay rates, whereas other modes with large shear contributions decay at much slower rates in the same liquid. The difference in decay rates may reach a factor of seven. Experimental observations are well supported by the analysis. The differences among modes are also found with liquid outside specific coating layers. Large changes in decay rates are observed when a phase transition between solid and liquid occurs outside the cladding boundary. The monitoring of multiple mode categories provides more complete assessment of outside media and enhances the capabilities of forward Brillouin scattering fiber sensors.

A continuous depth encoding PET detector using side readout of dual-layer GAGG crystals with SiPM array

A continuous depth encoding positron emission tomography (PET) detector using a side readout configuration with dual-layer GAGG scintillators of different decay times, coupled to a Silicon Photomultiplier (SiPM) array is proposed. The performance of the detector was evaluated through experimentation. The detector consists of an upper layer with a 1 × 4 fast decay GAGG (GAGG-F) crystal array and a lower layer with another 1 × 4 high-light-yield GAGG (GAGG-HL) crystal array. The 2 × 4 GAGG crystal array is then coupled to the 4 × 6 SiPM array. The SiPM array's sum signal is utilized for layer identification, while 24 individual signals are used to measure the 3D position of the gamma interaction. The experimental measurements demonstrate that the detector effectively resolves all crystal units and provides continuous depth information in the Z-direction. Utilizing the time over threshold method for dual-layer identification in coincidence mode yielded an accuracy of 96.4 %, whereas the pulse decay time method achieved an accuracy of 95.7 %. The average energy resolution was found to be 12.1 % and 11.2 % for the upper and lower GAGG crystal arrays, respectively. Using the maximum value-to-sum ratio method, the upper GAGG-F crystal layer displayed clear distinction and accurate assignment at two height positions, achieving a correct assignment rate of 90.5 %. In contrast, the lower GAGG-HL crystal layer exhibited poorer resolution at each height position, with correct assignment percentages dropping to 71.1 %. Employing the center of gravity position estimation method for the GAGG-F and GAGG-HL layers, the average Z spatial resolution was determined as 3.56 ± 0.33 mm (FWHM) and 3.35 ± 0.28 mm (FWHM).

Acquisition of complement fixing antibodies targeting Plasmodium falciparum merozoites in infants and their mothers in Uganda.

Antibody-mediated complement fixation has previously been associated with protection against malaria in naturally acquired immunity. However, the process of early-life development of complement-fixing antibodies in infants, both in comparison to their respective mothers and to other immune parameters, remains less clear. We measured complement-fixing antibodies in newborns and their mothers in a malaria endemic area over 5 years follow-up and found that infants' complement-fixing antibody levels were highest at birth, decreased until six months, then increased progressively until they were similar to birth at five years. Infants with high levels at birth experienced a faster decay of complement-fixing antibodies but showed similar levels to the low response group of newborns thereafter. No difference was observed in antibody levels between infant cord blood and mothers at delivery. The same result was found when categorized into high and low response groups, indicating placental transfer of antibodies. Complement-fixing antibodies were positively correlated with total schizont-specific IgG and IgM levels in mothers and infants at several time points. At nine months, complement-fixing antibodies were negatively correlated with total B cell frequency and osteopontin concentrations in the infants, while positively correlated with atypical memory B cells and P. falciparum-positive atypical memory B cells. This study indicates that complement-fixing antibodies against P. falciparum merozoites are produced in the mothers and placentally-transferred, and they are acquired in infants over time during the first years of life. Understanding early life immune responses is crucial for developing a functional, long lasting malaria vaccine.

Data-driven snapshot calibration via monotonic feature matching

Snapshot matrices of hyperbolic equations have a slow singular value decay, resulting in inefficient reduced-order models. We develop on the idea of inducing a faster singular value decay by computing snapshots on a transformed spatial domain, or the so-called snapshot calibration/transformation. We are particularly interested in problems involving shock collision, shock rarefaction-fan collision, shock formation, etc. For such problems, we propose a realizable algorithm to compute the spatial transform using monotonic feature matching. We consider discontinuities and kinks as features, and by carefully partitioning the parameter domain, we ensure that the spatial transform has properties that are desirable both from a theoretical and an implementation standpoint. We use these properties to prove that our method results in a fast Kolmogorov m-width decay of a calibrated manifold. A crucial observation we make is that due to calibration, the m-width does not only depend on m but also on the accuracy of the full-order model, which is in contrast to elliptic and parabolic problems that do not need calibration. The method we propose only requires the solution snapshots and not the underlying partial differential equation (PDE) and is therefore, data-driven. We perform several numerical experiments to demonstrate the effectiveness of our method.

Fully exposed (101) plane endowing CoSe anode with fast and stable potassium storage

Transition-metal selenides, especially cobalt selenides (CoSe), are widely regarded as a promising anode for potassium-ion batteries (KIBs) due to their high theoretical capacity and good electrical conductivity. However, CoSe easily suffers from a substantial volume change upon repeated cycling, leading to a fast capacity decay and poor cycling stability. Herein, a dual-carbon confined CoSe is successfully designed by using metal-organic frameworks as raw materials. Various characterizations disclose that the introduction of the extra carbon phase is conducive to the growth of (101) plane of CoSe, and based on this, rationally regulating carbonization temperature can further promote the exposure of (101) plane. Such fully exposed (101) plane not only provides sufficient active surface to uptake K-ions, but also favors the accommodation of electrode structure fluctuation, accounting for a high capacity and prolonged cycle lifespan. As a result, the optimized sample (denoted as 750 °CNC@CoSe/NC) delivers 392.5 mAh g−1 at 0.5 A g−1, accompanied by an excellent cycling stability over 400 cycles with 196.7 mAh g−1 at a high current density of 1 A g−1. This work is expected to offer effective guidance for constructing advanced CoSe anode toward KIBs.