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Pengpeng Zhang

Publications and source records attributed to Pengpeng Zhang.

14 recordsLinked to original sources
PubMed2026

Operando X-ray Spectroscopy Unveils Light-Driven Redox Selectivity for Photo-Assisted Li-S Batteries.

Photo-assisted lithium-sulfur batteries (PALSBs) can accelerate the sluggish redox kinetics of sulfur cathodes. However, the introduced light field inevitably complicates interfacial reactions, necessitating in situ evidence under realistic operating conditions. Here, we construct a TiO2/FePS3 (TF) p-n junction bifunctional photoelectrode and employ a multiphysics-coupled in situ x-ray spectroscopic technique to elucidate light-regulated catalysis from the interface into the bulk. Operando low-energy XPS identifies potential interfacial catalytic sites. High-energy operando XAFS is, for the first time, applied in PALSBs to track the K-edge position of catalytic centers throughout cycling. The results show that the reversible dynamic valence evolution synchronizes with the stepwise sulfur redox process, revealing that photogenerated carriers and electrocatalytic electrons act cooperatively to promote polysulfide conversion. DFT calculations corroborate, from thermodynamic and kinetic perspectives, that illumination strengthens polysulfide anchoring and lowers the energy barriers of key conversion steps, consistent with the operando spectroscopic observations. Benefiting from this photoelectrochemical co-regulation, the TF-based PALSB maintains excellent reversible capacity and cycling stability under high sulfur loading and low electrolyte content. This work establishes a characterization paradigm for the rational design of high-performance photo-assisted Li-S cathodes.

operando x‐ray spectroscopy↗
PubMed2006

Structural characterization of NDH-1 complexes of Thermosynechococcus elongatus by single particle electron microscopy.

The structure of the multifunctional NAD(P)H dehydrogenase type 1 (NDH-1) complexes from cyanobacteria was investigated by growing the wild type and specific ndh His-tag mutants of Thermosynechococcus elongatus BP-1 under different CO(2) conditions, followed by an electron microscopy (EM) analysis of their purified membrane protein complexes. Single particle averaging showed that the complete NDH-1 complex (NDH-1L) is L-shaped, with a relatively short hydrophilic arm. Two smaller complexes were observed, differing only at the tip of the membrane-embedded arm. The smallest one is considered to be similar to NDH-1M, lacking the NdhD1 and NdhF1 subunits. The other fragment, named NDH-1I, is intermediate between NDH-1L and NDH-1M and only lacks a mass compatible with the size of the NdhF1 subunit. Both smaller complexes were observed under low- and high-CO(2) growth conditions, but were much more abundant under the latter conditions. EM characterization of cyanobacterial NDH-1 further showed small numbers of NDH-1 complexes with additional masses. One type of particle has a much longer peripheral arm, similar to the one of NADH: ubiquinone oxidoreductase (complex I) in E. coli and other organisms. This indicates that Thermosynechococcus elongatus must have protein(s) which are structurally homologous to the E. coli NuoE, -F, and -G subunits. Another low-abundance type of particle (NDH-1U) has a second labile hydrophilic arm at the tip of the membrane-embedded arm. This U-shaped particle has not been observed before by EM in a NDH-I preparation.

Bacterial Proteins↗
PubMed2006

Electronic transport in nanometre-scale silicon-on-insulator membranes.

The widely used 'silicon-on-insulator' (SOI) system consists of a layer of single-crystalline silicon supported on a silicon dioxide substrate. When this silicon layer (the template layer) is very thin, the assumption that an effectively infinite number of atoms contributes to its physical properties no longer applies, and new electronic, mechanical and thermodynamic phenomena arise, distinct from those of bulk silicon. The development of unusual electronic properties with decreasing layer thickness is particularly important for silicon microelectronic devices, in which (001)-oriented SOI is often used. Here we show--using scanning tunnelling microscopy, electronic transport measurements, and theory--that electronic conduction in thin SOI(001) is determined not by bulk dopants but by the interaction of surface or interface electronic energy levels with the 'bulk' band structure of the thin silicon template layer. This interaction enables high-mobility carrier conduction in nanometre-scale SOI; conduction in even the thinnest membranes or layers of Si(001) is therefore possible, independent of any considerations of bulk doping, provided that the proper surface or interface states are available to enable the thermal excitation of 'bulk' carriers in the silicon layer.

Journal Article↗
PubMed2006

Novel lung IMRT planning algorithms with nonuniform dose delivery strategy to account for respiratory motion.

To effectively deliver radiation dose to lung tumors, respiratory motion has to be considered in treatment planning. In this paper we first present a new lung IMRT planning algorithm, referred as the dose shaping (DS) method, that shapes the dose distribution according to the probability distribution of the tumor over the breathing cycle to account for respiratory motion. In IMRT planning a dose-based convolution method was generally adopted to compensate for random organ motion by performing 4-D dose calculations using a tumor motion probability density function. We modified the CON-DOSE method to a dose volume histogram based convolution method (CON-DVH) that allows nonuniform dose distribution to account for respiratory motion. We implemented the two new planning algorithms on an in-house IMRT planning system that uses the Eclipse (Varian, Palo Alto, CA) planning workstation as the dose calculation engine. The new algorithms were compared with (1) the conventional margin extension approach in which margin is generated based on the extreme positions of the tumor, (2) the dose-based convolution method, and (3) gating with 3 mm residual motion. Dose volume histogram, tumor control probability, normal tissue complication probability, and mean lung dose were calculated and used to evaluate the relative performance of these approaches at the end-exhale phase of the respiratory cycle. We recruited six patients in our treatment planning study. The study demonstrated that the two new methods could significantly reduce the ipsilateral normal lung dose and outperformed the margin extension method and the dose-based convolution method. Compared with the gated approach that has the best performance in the low dose region, the two methods we proposed have similar potential to escalate tumor dose, but could be more efficient because dose is delivered continuously.

Algorithms↗
PubMed2005

Isolation, subunit composition and interaction of the NDH-1 complexes from Thermosynechococcus elongatus BP-1.

NDH (NADH-quinone oxidoreductase)-1 complexes in cyanobacteria have specific functions in respiration and cyclic electron flow as well as in active CO2 uptake. In order to isolate NDH-1 complexes and to study complex-complex interactions, several strains of Thermosynechococcus elongatus were constructed by adding a His-tag (histidine tag) to different subunits of NDH-1. Two strains with His-tag on CupA and NdhL were successfully used to isolate NDH-1 complexes by one-step Ni2+ column chromatography. BN (blue-native)/SDS/PAGE analysis of the proteins eluted from the Ni2+ column revealed the presence of three complexes with molecular masses of about 450, 300 and 190 kDa, which were identified by MS to be NDH-1L, NDH-1M and NDH-1S respectively, previously found in Synechocystis sp. PCC 6803. A larger complex of about 490 kDa was also isolated from the NdhL-His strain. This complex, designated 'NDH-1MS', was composed of NDH-1M and NDH-1S. NDH-1L complex was recovered from WT (wild-type) cells of T. elongatus by Ni2+ column chromatography. NdhF1 subunit present only in NDH-1L has a sequence of -HHDHHSHH- internally, which appears to have an affinity for the Ni2+ column. NDH-1S or NDH-1M was not recovered from WT cells by chromatography of this kind. The BN/SDS/PAGE analysis of membranes solubilized by a low concentration of detergent indicated the presence of abundant NDH-1MS, but not NDH-1M or NDH-1S. These results clearly demonstrated that NDH-1S is associated with NDH-1M in vivo.

Amino Acid Sequence↗
PubMed2005

Where to locate the isocenter? The treatment strategy for repeat trigeminal neuralgia radiosurgery.

PURPOSE: The purpose of this study is to investigate how the spatial relationship between the isocenters of the first and second radiosurgeries affects the overall outcome. METHODS AND MATERIALS: We performed a retrospective study on 40 patients who had repeat gamma knife radiosurgery for trigeminal neuralgia. Only one 4-mm isocenter was applied in both first and second radiosurgeries, with a maximum radiation dose of 75 Gy and 40 Gy, respectively. The MR scan of the first radiosurgery was registered to that of the second radiosurgery by a landmark-based registration algorithm. The spatial relationship between the isocenter of the first and the second radiosurgeries was thus determined. The investigating parameters were the distance between the isocenters of the two separate radiosurgeries and isocenter proximity to the brainstem. The outcome end points were pain relief and dysesthesias. The median follow-up for the repeat radiosurgery was 28 months (range, 6-51 months). RESULTS: Pain relief was complete in 11 patients, nearly complete (> or =90%) in 7 patients, partial (> or =50%) in 8 patients, and minimal (<50%) or none in another 14 patients. The mean distance between the two isocenters was 2.86 mm in the complete or nearly complete pain relief group vs. 1.93 mm in the others. Farther distance between isocenters was associated with a trend toward better pain relief (p = 0.057). The proximity of the second isocenter to the brainstem did not affect pain relief, and neither did placing the second isocenter proximal or distal to the brainstem compared with the first one. Three patients developed moderate dysesthesias (score of 4 on a 0-10 scale), and 2 other patients developed more significant dysesthesias (score of 7) after the second radiosurgery. Dysesthesias related neither to distance between isocenters nor to which isocenter was closer to the brainstem. CONCLUSIONS: Image registration between MR scans of the first and second radiosurgeries helps target delineation and radiosurgery treatment planning. Increasing the isocenter distance between the two radiosurgeries treated a longer segment of the trigeminal neuralgia nerve and was associated with a trend toward improved pain relief.

Adult↗
PubMed2005

Use of simulated annealing for optimization of alignment parameters in limited MRI acquisition volumes of the brain.

Studies suggest that clinical outcomes are improved in repeat trigeminal neuralgia (TN) Gamma Knife radiosurgery if a different part of the nerve from the previous radiosurgery is treated. The MR images taken in the first and repeat radiosurgery need to be coregistered to map the first radiosurgery volume onto the second treatment planning image. We propose a fully automatic and robust three-dimensional (3-D) mutual information- (MI-) based registration method engineered by a simulated annealing (SA) optimization technique. Commonly, Powell's method and Downhill simplex (DS) method are most popular in optimizing the MI objective function in medical image registration applications. However, due to the nonconvex property of the MI function, robustness of those two methods is questionable, especially for our cases, where only 28 slices of MR T1 images were utilized. Our SA method obtained successful registration results for all the 41 patients recruited in this study. On the other hand, Powell's method and the DS method failed to provide satisfactory registration for 11 patients and 9 patients, respectively. The overlapping volume ratio (OVR) is defined to quantify the degree of the partial volume overlap between the first and second MR scan. Statistical results from a logistic regression procedure demonstrated that the probability of a success of Powell's method tends to decrease as OVR decreases. The rigid registration with Powell's or the DS method is not suitable for the TN radiosurgery application, where OVR is likely to be low. In summary, our experimental results demonstrated that the MI-based registration method with the SA optimization technique is a robust and reliable option when the number of slices in the imaging study is limited.

Algorithms↗
PubMed2004

Identification of NdhL and Ssl1690 (NdhO) in NDH-1L and NDH-1M complexes of Synechocystis sp. PCC 6803.

The subunit compositions of two types of NAD(P)H dehydrogenase complexes of Synechocystis sp. PCC 6803, NDH-1L and NDH-1M, were studied by two-dimensional blue-native/SDS-PAGE followed by electrospray tandem mass spectrometry. Fifteen proteins were observed in NDH-1L including hydrophilic subunits (NdhH, -K, -I, -J, -M, and -N) and hydrophobic subunits (NdhA, -B, -E, -G, -D1, and -F1). In addition, NdhL and a novel subunit, Ssl1690 (designated NdhO), were shown to be components of this complex. All subunits mentioned above were present in the NDH-1M complex except NdhD1 and NdhF1. NdhL and Ssl1690 (NdhO) were homologous to hypothetical proteins encoded by genomic DNA in higher plants, suggesting that chloroplast NDH-1 complexes contain related subunits. Diagnostic sequence motifs were found for both NdhL and NdhO homologous proteins. Analysis of ndhL deletion mutant (M9) revealed the presence of assembled NDH-1L and NDH-1M complexes, but these complexes appear to be functionally impaired in the absence of NdhL. Both NDH-1 complexes were absent in the ndhB deletion mutant (M55).

Amino Acid Sequence↗
PubMed2004

Expression and functional roles of the two distinct NDH-1 complexes and the carbon acquisition complex NdhD3/NdhF3/CupA/Sll1735 in Synechocystis sp PCC 6803.

To investigate the (co)expression, interaction, and membrane location of multifunctional NAD(P)H dehydrogenase type 1 (NDH-1) complexes and their involvement in carbon acquisition, cyclic photosystem I, and respiration, we grew the wild type and specific ndh gene knockout mutants of Synechocystis sp PCC 6803 under different CO2 and pH conditions, followed by a proteome analysis of their membrane protein complexes. Typical NDH-1 complexes were represented by NDH-1L (large) and NDH-1M (medium size), located in the thylakoid membrane. The NDH-1L complex, missing from the DeltaNdhD1/D2 mutant, was a prerequisite for photoheterotrophic growth and thus apparently involved in cellular respiration. The amount of NDH-1M and the rate of P700+ rereduction in darkness in the DeltaNdhD1/D2 mutant grown at low CO2 were similar to those in the wild type, whereas in the M55 mutant (DeltaNdhB), lacking both NDH-1L and NDH-1M, the rate of P700+ rereduction was very slow. The NDH-1S (small) complex, localized to the thylakoid membrane and composed of only NdhD3, NdhF3, CupA, and Sll1735, was strongly induced at low CO2 in the wild type as well as in DeltaNdhD1/D2 and M55. In contrast with the wild type and DeltaNdhD1/D2, which show normal CO2 uptake, M55 is unable to take up CO2 even when the NDH-1S complex is present. Conversely, the DeltaNdhD3/D4 mutant, also unable to take up CO2, lacked NDH-1S but exhibited wild-type levels of NDH-1M at low CO2. These results demonstrate that both NDH-1S and NDH-1M are essential for CO2 uptake and that NDH-1M is a functional complex. We also show that the Na+/HCO3- transporter (SbtA complex) is located in the plasma membrane and is strongly induced in the wild type and mutants at low CO2.

Carbon↗
PubMed2004

Towards functional proteomics of membrane protein complexes in Synechocystis sp. PCC 6803.

The composition and dynamics of membrane protein complexes were studied in the cyanobacterium Synechocystis sp. PCC 6803 by two-dimensional blue native/SDS-PAGE followed by matrix-assisted laser-desorption ionization time of flight mass spectrometry. Approximately 20 distinct membrane protein complexes could be resolved from photoautotrophically grown wild-type cells. Besides the protein complexes involved in linear photosynthetic electron flow and ATP synthesis (photosystem [PS] I, PSII, cytochrome b6f, and ATP synthase), four distinct complexes containing type I NAD(P)H dehydrogenase (NDH-1) subunits were identified, as well as several novel, still uncharacterized protein complexes. The dynamics of the protein complexes was studied by culturing the wild type and several mutant strains under various growth modes (photoautotrophic, mixotrophic, or photoheterotrophic) or in the presence of different concentrations of CO2, iron, or salt. The most distinct modulation observed in PSs occurred in iron-depleted conditions, which induced an accumulation of CP43' protein associated with PSI trimers. The NDH-1 complexes, on the other hand, responded readily to changes in the CO2 concentration and the growth mode of the cells and represented an extremely dynamic group of membrane protein complexes. Our results give the first direct evidence, to our knowledge, that the NdhF3, NdhD3, and CupA proteins assemble together to form a small low CO2-induced protein complex and further demonstrate the presence of a fourth subunit, Sll1735, in this complex. The two bigger NDH-1 complexes contained a different set of NDH-1 polypeptides and are likely to function in respiratory and cyclic electron transfer. Pulse labeling experiments demonstrated the requirement of PSII activity for de novo synthesis of the NDH-1 complexes.

Adenosine Triphosphate↗
PubMed2004

AAPM TG-43 formalism for brachytherapy dose calculation of a 137Cs tube source.

We present a development of the use of the AAPM TG-43 dose formalism applied to 137Cs gynecological implant sources. The geometry factor, radial dose function, and anisotropy function of a 137Cs source modeled after the Nuclear Associates 67-809 series stainless steel jacketed tube source were derived following the AAPM TG-43 formalism. The dose rate distribution through the center of the source using the AAPM TG-43 dose formalism is calculated and compared with the calculations obtained using the Sievert summation and Monte Carlo simulation. The three methods resulted in an agreement within less than 5%, or an isodose rate line agreement within 2 mm. We demonstrate that the AAPM TG-43 formalism can be applied to 137Cs linear sources and is capable of serving as a 137Cs dose calculation algorithm that can be used for treatment planning purpose.

Brachytherapy↗
PubMed2003

Plug pattern optimization for gamma knife radiosurgery treatment planning.

PURPOSE: To develop a novel dose optimization algorithm for improving the sparing of critical structures during gamma knife radiosurgery by shaping the plug pattern of each individual shot. METHOD AND MATERIALS: We first use a geometric information (medial axis) aided guided evolutionary simulated annealing (GESA) optimization algorithm to determine the number of shots and isocenter location, size, and weight of each shot. Then we create a plug quality score system that checks the dose contribution to the volume of interest by each plug in the treatment plan. A positive score implies that the corresponding source could be open to improve tumor coverage, whereas a negative score means the source could be blocked for the purpose of sparing normal and critical structures. The plug pattern is then optimized via the GESA algorithm that is integrated with this score system. Weight and position of each shot are also tuned in this procedure. RESULTS: An acoustic tumor case is used to evaluate our algorithm. Compared to the treatment plan generated without plug patterns, adding an optimized plug pattern into the treatment planning process boosts tumor coverage index from 95.1% to 97.2%, reduces RTOG conformity index from 1.279 to 1.167, lowers Paddick's index from 1.34 to 1.20, and trims the critical structure receiving more than 30% maximum dose from 16 mm(3) to 6 mm(3). CONCLUSIONS: Automated GESA-based plug pattern optimization of gamma knife radiosurgery frees the treatment planning team from the manual forward planning procedure and provides an optimal treatment plan.

Algorithms↗
PubMed2002

Implementation of the isocenter-shift technique for smoothing MLC field edge on a 3D treatment planning system.

Stepped leaf edges are the major limitation of conforming to the prescribed treatment contour defined by the conventional multileaf collimator (MLC), which produces a scalloped dose pattern. The commercial HD-270 MLC (HDI) technique provides a software solution of the conventional MLC to achieve smoothed edge and optimal penumbra of the MLC shaped field. We implemented the HDI functionality on a 3D treatment planning system and compared the dosimetric effects of the HDI delivery in simulation with those in experiment for a number of the MLC fields. The fields from the contour of varied shapes with different sizes of the leaf stepping were tested for the HDI delivery. There is a good agreement of the dose distribution between the calculation as implemented in the planning system and the measurement performed on the treatment machine. It has been shown that the HDI delivery significantly smooths the stepped field edge with the reduced isodose undulation and effective penumbra. A problem may be present when the HDI is applied for the treatment of the circular contour of smaller diameter, and the conformity of the MLC shaping may not be achievable satisfactorily with the existing system. The optimization of leaf configuration is suggested to improve the conformity of the HDI technique. The HDI planning then can be used to assist in the decision making of applying the HDI treatment delivery.

Humans↗