Fast Decay Research Articles

Fractal Bloch model to characterize stretched magnetization relaxation in magnetic resonance imaging

This study proposes a fractal Bloch model to describe the stretched magnetization relaxation in magnetic resonance imaging (MRI). The fractal Bloch model extends the relaxation terms and preserves the linear Larmor precession terms under a constant magnetic field. The solutions of the fractal Bloch model have the form of stretched exponential and converge to the exponential form for the classical Bloch equation when the orders of the fractal derivative α=1, and β=1. The results show that the damped oscillations in Mx(t) or My(t) have a faster decay at short times, and slower decay at long times with the increasing values of α. The relaxation of Mz(t) with the stretched-exponential form increases more quickly than the exponential case at first, but then converges more slowly to the equilibrium magnetization, which needs a longer time to return the equilibrium in the cases of smaller order β. The fractal Bloch model is verified to characterize the signal decays in rat brain and bovine nasal cartilage. The fitting results show that the fractal Bloch model is effective to describe the stretched magnetization relaxation in MRI data. Thus, the fractal derivative is an alternative tool to use to understand MRI in complex systems, and its order can serve as an index to distinguish different relaxation processes in magnetization.

Photoluminescence and scintillation properties of Ce-doped Al(PO3)3–MPO3 (M = K, Rb, Cs) glass scintillators for gamma- and X-ray detection

Scintillators are used as radiation detectors because they absorb ionizing radiation and release energy as light. Inorganic glasses have significant advantages over inorganic crystals owing to their ease of fabrication, low cost, controllable shape, and thermal and chemical durability. However, large performance gaps, such as light yield and density, still exist between inorganic glasses and commercial inorganic crystals. Here, we present a demonstration of an inorganic scintillator based on phosphate glass with an alkali metal as the host and Ce3+ as the emission centers. This glass exhibits a high light yield of 2500 photons/MeV, which is higher than that of previously reported inorganic glass scintillators (approximately 2000 photons/MeV). The glass is transparent and has a fast decay time of approximately 30 ns, which is attributed to the 5d–4f optical transition of Ce3+, facilitating applications for inorganic glass scintillators for gamma- and X-ray detection. Furthermore, we investigated the difference in the energy-transfer efficiency of the fabricated inorganic glasses by changing the alkali metals. The energy transfer efficiency increases with an increase in the atomic number of the alkali metals; the thermoluminescence (TL) intensity decreases with an increase in the atomic number of the alkali metals. These results suggest that Cs is an optimum alkali metal to achieve a high light yield on phosphate glass scintillators, and they may be related to the difference in the number of electron–hole pairs that do not contribute to scintillation.

Nonlinear inertia and its effect within an X-shaped mechanism – Part II: Nonlinear influences and experimental validations

In this study, the effects of nonlinear inertia are further investigated and verified with prototyping and experimental validation. The new inertia unit integrated within a well-designed X-shaped mechanism can produce 3 different typical nonlinear inertia forms which have different nonlinear influence on dynamic response. A critical parametric indicator (Ratio of Inertia) is thus proposed to identify and indicate different types of nonlinearities and a new performance assessment indicator (F-stability) is proposed to assess the performance improvement compared to different nonlinearity with respect to linear counterparts in a dynamic excitation sense. A method for testing different nonlinear inertia is also proposed. It is uniquely revealed that (a) the Ratio of Inertia can be well used to tune different types of inertia nonlinearities; (b) the symmetrical nonlinear inertia (HCHE-type) is generally better in vibration isolation with smaller peak/anti-peak values, peak/anti-peak frequencies (∼ 1 Hz and 3∼4Hz in our prototype), and faster decay rate (∼ -50dB/Dec with our prototype) but higher high-frequency transmissibility compared to the two asymmetric nonlinearities; (c) the nonlinear inertia contributes significantly to tune the interactive force between vibration source and object in the low frequency range (<10Hz in our prototype) and obviously helpful and robust to stronger excitations. All the theoretical analysis results are verified with our developed prototype. These results should for the first time provide a comprehensive and in-depth understanding of nonlinear inertia and its effects in different cases and thus definitely shed light on various engineering applications.

Steady-state and dynamic characteristics of deep UV luminescence in rock salt-structured MgxZn1−xO

Temperature-dependent cathodoluminescence spectra were measured for rock salt-structured MgxZn1−xO films with x = 0.95–0.61. The Mg0.95Zn0.05O film exhibited the shortest deep UV peak wavelength of 199 nm (6.24 eV) at 6 K. Relatively high equivalent internal quantum efficiencies of 0.9%–11% were obtained. The Tauc plots, which were obtained from temperature-dependent optical transmittance measurements, exhibited large Stokes-like shifts of 0.7–0.9 eV at 6–300 K. Time-resolved photoluminescence (PL) signals at 7 K exhibited fast and slow decay components. The fast decay component had PL lifetimes of 2.59–3.08 ns, and the slow decay component far exceeded the measurement time range of 12.5 ns. The fast decay constant reflected the transfer lifetime of the photoexcited carriers to certain trapping centers. These centers were tentatively ascribed to Zn-related isoelectronic trapped-hole centers and may be a cause of the large Stokes-like shifts. The signals at 300 K exhibited very short PL lifetimes of 120–180 ps. The PL lifetimes were mainly attributed to the nonradiative recombination lifetime. Simultaneous decreases in the Zn-related isoelectronic trapped-hole centers and the nonradiative recombination centers were found to be necessary to improve the DUV emission properties of RS-MgxZn1−xO films.

Steric groups fusion strategy for green multi-resonance emitters toward efficient OLEDs with narrowband emission

Multi-resonance induced thermally activated delayed fluorescence (MR-TADF) emitters have demonstrated significant advantages in high-efficient organic light-emitting diodes (OLEDs) with wide color gamut due to their high photoluminescence quantum yields (ΦPL) and narrow spectra. Herein, two novel green MR-TADF emitters, MFCzBN and SFCzBN, were designed and synthesized by integrating steric groups into the classic framework of BNCz. These emitters exhibited narrowband green emission both in solution and films, fast radiative decay rates of approximately 108 s−1, as well as high ΦPL values of up to 90%. The fabricated vacuum-deposited OLEDs displayed bright green emission at 508 nm, achieving remarkable maximum external quantum efficiencies (EQEmax) of 24.3% and 24.7% for MFCzBN and SFCzBN, respectively. Notably, the MFCzBN-based device demonstrated low efficiency roll-off values of 1.6% and 2.5% at practical luminance of 100 cd m−2 and 1000 cd m−2. This work presents an effective strategy for attaining high-efficiency MR-OLEDs through the fusion of steric groups.

Hierarchically cobalt phosphide nanostructures embedded in N, P co-doped porous carbon networks assembled by ultrathin sheets for high-performance Li/Na-ion batteries

Metal phosphides have aroused tremendous interests for energy storages, owing to their unique crystal structure and high theoretical specific capacity. However, poor cycling stability and fast capacity decay inhibit their application. Herein, we successfully synthesized a novel heterostructural architecture with well-dispersed CoP nanoparticles (NPs) embedded in 3-dimential (3D) N, P co-doped porous carbon (NP-PC) networks by a facile polymer-derived route. The unique 3D NP-PC networks can mitigate the volume change, enhance conductivity, and provide electron/ion transport channels. The as-prepared heterostructure exhibits the synergistic effect between CoP NPs and NP-PC, relieves CoP NPs agglomeration, and stabilizes the surface/interface structure. Benefiting from these advantages, the heterostructural architecture exhibits superior electrochemical activities and cycling stability for lithium storage (1056 mAh·g−1 at 0.2 A·g−1 after 200 cycles) and sodium storage (345 mAh·g−1 at 0.2 A·g−1 after 60 cycles). This work aids the construction of high-performance metal phosphide-based anode materials.

Disrupting Dimeric β-Amyloid by Electric Fields.

The early oligomers of the amyloid Aβ peptide are implicated in Alzheimer's disease, but their transient nature complicates the characterization of their structure and toxicity. Here, we investigate the stability of the minimal toxic species, i.e., β-amyloid dimers, in the presence of an oscillating electric field. We first use deep learning (AlphaFold-multimer) for generating initial models of Aβ42 dimers. The flexibility and secondary structure content of the models are then analyzed by multiple runs of molecular dynamics (MD). Structurally stable models are similar to ensemble representatives from microsecond-long MD sampling. Finally, we employ the validated model as the starting structure of MD simulations in the presence of an external oscillating electric field and observe a fast decay of β-sheet content at high field strengths. Control simulations using the helical dimer of the 42-residue leucine zipper peptide show higher structural stability than the Aβ42 dimer. The simulation results provide evidence that an external electric field (oscillating at 1 GHz) can disrupt amyloid oligomers which should be further investigated by experiments with brain organoids in vitro and eventually in vivo.

Fast Ce,Ca:LuAG scintillation ceramics for HEP: Fabrication, characterization, and computation

AbstractHigh‐energy physics community is looking for a hard, fast, and low‐cost scintillation material, and Ce:Lu3Al5O12 (Ce:LuAG) ceramic is one of the competitive candidates. This work presents Ce,Ca:LuAG scintillation ceramics with good optical quality, and the influence of Ce and Ca concentrations on optical and scintillation properties was fully analyzed. At relatively low level of Ce concentration, the less Ca2+ content is needed to achieve a significant intensity increase in fast scintillation component while maintaining a relatively high light yield (LY). The introduction of only 0.1 at% Ca2+ could increase the LY0.5 μs/LY3.0 μs from 79.9% to 96.1% in Ce,Ca:LuAG ceramics of 0.1 at% Ce. First‐principles investigations are further performed to reveal the tuning mechanisms of the scintillation properties of LuAG by Ce and Ca codoping. We show that the Fermi level shifts down with Ca codoping, which increases the Ce4+ content and decreases the depth of the electron traps (VO), resulting to a faster decay. Moreover, the formation preference of Ca‐VO complexes over Ce‐VO leads to the suppression of the non‐radiative decay of Ce via VO. In summary, our study demonstrates the realization of the performance tuning of LuAG via Ce and Ca codoping.

Study of the evolution of pulsed plasma under an external longitudinal magnetic field

An experimental study on the role of an external longitudinal magnetic field on the characteristics changes of pulsed plasma stream, produced in argon medium, is carried out at different time spans of its evolution. The spectroscopic observations are time integrated and are carried out at different times of plasma formation for pulsed discharge. This study gives insights into the recombination and diffusion phase of the plasma species in the presence of the magnetic field. The transition of plasma species from a dominant recombination phase to a diffusional phase is well revealed by the density profile during the time evolution. Moreover, the decrease in electron temperature and the increase in electron excitation temperature explain the energy transfer to electrons due to metastable quenching, and the system gradually approaches equilibrium. The magnetic field also affects the transitions of the ionized argon population between different energy levels. It is found that faster decay occurs for transitions of different plasma species to non-metastable states, while the populations of metastable states exist for a longer time. In addition, the time-resolved morphology changes of the plasma stream are also observed by high speed imaging, which shows the flow structure of the plasma stream at different time frames. The imaging of the plasma stream evolution shows the initial ejection of the plasma sheet from the electrode assembly, its detachment, the steady flow, and gradually its nature of dying out.

Metalloporphyrin conjugated porous polymer in-situ grown on a Celgard separator as multifunctional polysulfide barrier and catalyst for high-performance Li-S batteries

The severe shuttling of soluble polysulfides (LiPSs) (Li2Sx, 4 ≤ x ≤ 8) and sluggish kinetics of solid–solid conversion (Li2S2 → Li2S), lead to the premature end of discharge, resulting in fast capacity decay, limiting the practical performance and safety of lithium-sulfur batteries (LSBs). Functional modifiers on separators exhibit significant performances in migrating diffusion and promoting conversion for LiPSs; thus, endowing the separator with multiple high-performance parameters by multifactorial engineering to address the two issues mentioned above is an urgent need. Herein, for the first time, an ultra-light (≈0.14 mg cm−2) and multifunctional modifier consisting of metalloporphyrin conjugated porous polymer (Al-CPP) is interface-induced growth on the commercial separator to develop advanced LSBs. The electrocatalyst of metalloporphyrin is covalently constructed by an imidazolium-containing linker with bis(trifluoromethane)sulfonimide (TFSI−) anions within the porous skeleton, improving diffusion and conversion of LiPSs as well as facilitating electrolyte accessibility and Li+ transport, thereby performing enhanced full-range sulfur redox kinetics, and guiding uniform Li deposition. The in-situ growth of metalloporphyrin conjugated porous polymer is further verified in LSBs that realize superior rate performances and long lifespans. This contribution proposes an efficient in-situ growth of an ultra-light modifier design strategy to functionalize separators and inspires multi-function synergetic integration facing high-performance LSBs.

Modelling the effect of bromide on chlorine decay in raw and coagulated surface waters

A novel and simple semi-mechanistic model describing the effect of bromide on chlorine decay was developed. A well validated two-reactant parallel second order (2R) chlorine decay model is available for planning and operation. Four parameters - reaction rate coefficients and initial concentrations of fast and slow reacting compounds - define the model. Bromide concentration varies in water bodies but considering the variability requires conducting individual tests and parameter estimation for each bromide concentration. The proposed model was developed and tested using data obtained from six water sources from the US and Australia. The samples included a mix of raw and coagulated waters with different pH (7.5–8.0), DOC (1.43–5.54 mg-C/L), SUVA (1.73–2.90), chlorine dose (2.32–8.29 mg/L), bromide (14–844 μg/L), chlorine to bromide ratios (4.7–230.4), and temperatures (20–23 °C). when it was assumed that the initial concentrations of fast and slow reacting compounds would not be affected by the addition of bromide, a linear relationship was established between fast and slow decay rate coefficients and the initial bromide concentration in each water source. The linearity coefficient (β) ranged from 1.73 ± 7.24E-04 to 3.56 ± 1.79E-03 L/μg-Br, but a common value of 3.00E-03 ± 5.79E-04 described the effect of bromide in all four tested sources (DOC 1.43–5.54 mg/L) from the US at pH 8 units and 20 °C. This model simplifies the consideration of the effect of bromide in chlorine decay and reduces the number of tests and parameters required to simulate water supply systems that incorporate the effect of bromide.

Exact decay rates for weakly coupled systems with indirect damping by fractional memory effects

AbstractThis paper deals with the asymptotic behavior of a weakly coupled system of two equations in which one of them has a dissipative mechanism given by a memory term. This term depends on the fractional operator with exponent . We show that strong solutions of the system decay polynomially with a rate that depends on both the exponent θ and wave propagation speeds. Optimal decay rates are found and the results show a surprising aspect: More regular damping does not necessarily imply a faster decay.

Glucose versus fructose metabolism in the liver measured with deuterium metabolic imaging.

Chronic intake of high amounts of fructose has been linked to the development of metabolic disorders, which has been attributed to the almost complete clearance of fructose by the liver. However, direct measurement of hepatic fructose uptake is complicated by the fact that the portal vein is difficult to access. Here we present a new, non-invasive method to measure hepatic fructose uptake and metabolism with the use of deuterium metabolic imaging (DMI) upon administration of [6,6'-2H2]fructose. Using both [6,6'-2H2]glucose and [6,6'-2H2]fructose, we determined differences in the uptake and metabolism of glucose and fructose in the mouse liver with dynamic DMI. The deuterated compounds were administered either by fast intravenous (IV) bolus injection or by slow IV infusion. Directly after IV bolus injection of [6,6'-2H2]fructose, a more than two-fold higher initial uptake and subsequent 2.5-fold faster decay of fructose was observed in the mouse liver as compared to that of glucose after bolus injection of [6,6'-2H2]glucose. In contrast, after slow IV infusion of fructose, the 2H fructose/glucose signal maximum in liver spectra was lower compared to the 2H glucose signal maximum after slow infusion of glucose. With both bolus injection and slow infusion protocols, deuterium labeling of water was faster with fructose than with glucose. These observations are in line with a higher extraction and faster turnover of fructose in the liver, as compared with glucose. DMI with [6,6'-2H2]glucose and [6,6'-2H2]fructose could potentially contribute to a better understanding of healthy human liver metabolism and aberrations in metabolic diseases.

Inactivation of Salmonella Typhimurium in fresh-cut lettuce during chlorine washing: Assessing the impacts of free chlorine concentrations and exposure times

The aim of this study was to evaluate, quantify and model the inactivation of Salmonella in fresh-cut lettuce during washings with chlorinated water at different free chlorine concentrations (FCC, 0–150 mg/L). Individual fresh-cut lettuce samples (4 cm2) were inoculated with a Salmonella culture (ca. 4 log CFU/cm2) and washed with 100-mL solutions with different FCC for different times (0–150 s). The surviving Salmonella cells recovered from samples were enumerated by plate count methodology. A fast decay on Salmonella counts was marked in the first 20 s of washing, followed by a slowing down on reductions. A maximum of 2.6 log-decrease was observed after 2.5-min washing regardless of FCC. The log-linear with tail primary model coupled with a linear secondary model was fitted to inactivation data obtained at FCC from 50 to 150 mg/L through global regression analysis, yielding a suitable model to describe Salmonella concentrations as a function of FCC and washing times (RMSE = 0.34, R2adj = 0.84). Simulations using the developed model showed inactivation rates varying from 0.17 log CFU/s at 50 mg/L to 0.86 log CFU/s at 150 mg/L. Disinfection models on lettuce are valuable tools for the validation of control measures in the fresh-cut produce industry and for quantitative risk assessments.

On a Reduced Component-by-Component Digit-by-Digit Construction of Lattice Point Sets

Abstract In this paper, we study an efficient algorithm for constructing point sets underlying quasi-Monte Carlo integration rules for weighted Korobov classes. The algorithm presented is a reduced fast component-by-component digit-by-digit (CBC-DBD) algorithm, which is useful for situations where the weights in the function space show a sufficiently fast decay. The advantage of the algorithm presented here is that the computational effort can be independent of the dimension of the integration problem to be treated if suitable assumptions on the integrand are met. By considering a reduced digit-by-digit construction, we allow an integration algorithm to be less precise with respect to the number of bits in those components of the problem that are considered less important. The new reduced CBC-DBD algorithm is designed to work for the construction of lattice point sets, and the corresponding integration rules (so-called lattice rules) can be used to treat functions in different kinds of function spaces. We show that the integration rules constructed by our algorithm satisfy error bounds of almost optimal convergence order. Furthermore, we give details on an efficient implementation such that we obtain a considerable speed-up of a previously known CBC-DBD algorithm that has been studied in the paper Digit-by-digit and component-by-component constructions of lattice rules for periodic functions with unknown smoothness by Ebert, Kritzer, Nuyens, and Osisiogu, published in the Journal of Complexity in 2021. This improvement is illustrated by numerical results.

Integration of a Groundwater Model to the Noah Land Surface Model for Aquifer‐Soil Interaction

AbstractSoil water‐groundwater interactions are important in determining the moisture profile in a soil column. However, the Noah Land Surface Model (Noah LSM), the land surface component of several general circulation models, does not consider groundwater effects. The present study investigates the impact of integrating a groundwater model into the Noah LSM. By performing experiments forced by observations at the surface, insights into the characteristics of soil moisture evolution with and without the aquifer are investigated. In the absence of surface precipitation, soil moisture is shown to exhibit an exponential decay rate without the aquifer (termed as Noah‐Cntl). This is because evapotranspiration dominates other processes governing the soil moisture evolution. Based on scale analysis, we derived an analytical equation that could well represent the aforementioned exponential variation in soil moisture. Presence of the aquifer (termed as Noah‐GW) makes the capillary processes important as well. The result is a slower decay of soil moisture as compared to Noah‐Cntl without surface precipitation. Soil moisture evolution in both the models is a function of vegetation and soil types. As a result, the aforementioned decay timescale displays significant heterogeneity over the Indian region, with Central India exhibiting relatively faster decay rates. We also performed 24‐year long experiments with observed interannually varying forcing that indicates an enhancement in the annual mean soil moisture at all levels due to groundwater effects. This enhancement is particularly prominent during the post‐monsoon season, reaffirming the results of the drain‐out experiments mentioned above.

Proportional-Integral Observer Design for Multirate-Networked Systems Under Constrained Bit Rate: An Encoding-Decoding Mechanism.

In this article, the proportional-integral observer design problem is studied for a class of multirate networked systems subject to constrained bit rate. The sensor sampling period is allowed to be different from the system updating period and, to facilitate the observer design, the underlying multirate system is cast into a general single-rate one by resorting to the lifting technique. In order to curb the communication burden and promote the data security, the encoding-decoding procedure is implemented on the sensor-to-observer channel to convert the measurement signals into binary codewords. A sufficient condition is first proposed to reveal the fundamental relationship between the bit-rate constraints and the decoding accuracy, and then the exponentially ultimate boundedness of the error dynamics is assessed with the aid of the Lyapunov method. Subsequently, the desired observer gains are determined by solving two optimization problems with the aim to achieve two distinct performance indices, namely, the smallest ultimate bound and the fastest decay rate. Finally, the validity of the developed observer design approach is thoroughly demonstrated via the simulation examples.

Strong metal oxide-support interaction in MoO2/N-doped MCNTs heterostructure for boosting lithium storage performance

The low-rate capability and fast capacity decaying of the molybdenum dioxide anode material have been a bottleneck for lithium-ion batteries (LIBs) due to low carrier transport, drastic volume expansion and inferior reversibility. Furthermore, the lithium-storage mechanism is still controversial at present. Herein, we fabricate a new kind of MoO2 nanoparticles with nitrogen-doped multiwalled carbon nanotubes (MoO2/N-MCNTs) as anode for LIBs. The strong chemical bonding (MoOC) endows MoO2/N-MCNTs a strong metal oxide–support interaction (SMSI), rendering electron/ion transfer and facilitate significant Li+ intercalation pseudocapacitance, which is evidenced by both theoretical computation and detailed experiments. Thus, the MoO2/N-MCNTs exhibits high-rate performance (523.7 mAh/g at 3000 mA g−1) and long durability (507.8 mAh/g at 1000 mA g−1 after 500 cycles). Furthermore, pouch-type full cell composed of MoO2/N-MCNTs anodes and commercial LiNi0.6Co0.2Mn0.2O2 (NCM622) cathodes demonstrate impressive rate performance and cyclic life, which displays an unparalleled energy density of 553.0 Wh kg−1. Ex-situ X-ray absorption spectroscopy (XAS) indicates the enhanced lithium-storage mechanism is originated from a partially irreversible phase transition from Li0.98MoO2 to Li2MoO4 via delithiation. This work not only provides fresh insights into the enhanced lithium-storage mechanism but also proposes new design principles toward efficient LIBs.

Nanocomposite scintillation perovskite-delignified wood photonic guides for X-ray imaging

Nanocrystalline scintillators with low-cost, fast response, and high light yield are widely used for X-ray imaging. However, they fail in high-energy X-ray imaging because of the fundamental limitations due to lateral radiation spreading in thicker device-compatible active layers. This issue is resolved by using the novel nanocomposite containing CsPbBr3 scintillation single-microcrystalites embedded into transparent, natural wood-derived light-guiding fibrous structures. The CsPbBr3 crystals convert X-ray to visible photons with a high photoluminescence quantum efficiency (76 %), and an average fast photoluminescence decay time of 25.9 ns. The delignified wood-derived fiber-like lumina effectively guide light, while suppressing the lateral spreading of scintillation photons. This unique porous nanocomposite material offers an excellent X-ray detection performance, and linear response in a wide parameter range. The developed scintillator screen achieves well-resolved, high-contrast X-ray imaging, featuring a very high spatial resolution of 11.9 lp/mm at a modulation transfer function of 0.2, thus exceeding the benchmark industry standards and offering a new advanced materials platform for radiation detection and dosimetry applications.

Thermonuclear type-I X-ray bursts and burst oscillations from the eclipsing AMXP swift J1749.4–2807

ABSTRACT Swift J1749.4-2807 is the only known eclipsing accreting millisecond X-ray pulsar. In this paper, we report on seven thermonuclear (Type-I) X-ray bursts observed by NICER during its 2021 outburst. The first six bursts show slow rises and long decays, indicative of mixed H/He fuel, whereas the last burst shows fast rise and decay, suggesting He-rich fuel. Time-resolved spectroscopy of the bursts revealed typical phenomenology (i.e. an increase in blackbody temperature during the burst rise, and steady decrease in the decay), however, they required a variable NH. We found that the values of NH during the bursts were roughly double those found in the fits of the persistent emission prior to each burst. We interpret this change in absorption as evidence of burst–disc interaction, which we observe due to the high inclination of the system. We searched for burst oscillations during each burst and detected a signal in the first burst at the known spin frequency of the neutron star (517.92 Hz). This is the first time burst oscillations have been detected from Swift J1749.4-2807. We further find that each X-ray burst occurs on top of an elevated persistent count rate. We performed time-resolved spectroscopy on the combined data of the bursts with sufficient statistics (i.e. the clearest examples of this phenomenon) and found that the blackbody parameters evolve to hotter temperatures closer to the onset of the bursts. We interpret this as a consequence of an unusual marginally stable burning process similar to that seen through mHz QPOs.