Thermodynamic Quasi-equilibrium Research Articles

Identification of Two Regimes of Carrier Thermalization in PbS Nanocrystal Assemblies

We bring fresh insight into the ensemble properties of PbS colloidal quantum dots with a critical review of the literature on semiconductors followed by systematic comparisons between steady-state photocurrent and photoluminescence measurements. Our experiments, performed with sufficiently low powers to neglect nonlinear effects, indicate that the photoluminescence spectra have no other noticeable contribution beside the radiative recombination of thermalized photocarriers (i.e., photocarriers in thermodynamic quasi-equilibrium). A phenomenological model based on the local Kirchhoff law is proposed that makes it possible to identify the nature of the thermalized photocarriers and to extract their temperatures from the measurements. Two regimes are observed: For highly compact assemblies of PbS quantum dots stripped from organic ligands, the thermalization concerns photocarriers distributed over a wide energy range. With PbS quantum dots cross-linked with 1,2-ethanedithiol or longer organic ligand chains, the thermalization concerns solely the fundamental exciton and can quantitatively explain all the observations, including the precise Stokes shift between the absorbance and luminescence maxima.

Intact Transition Epitope Mapping - Thermodynamic Weak-force Order (ITEM - TWO)

We have developed an electrospray mass spectrometry method which is capable to determine antibody affinity in a gas phase experiment. A solution with the immune complex is electrosprayed and multiply charged ions are translated into the gas phase. Then, the intact immune-complex ions are separated from unbound peptide ions. Increasing the voltage difference in a collision cell results in collision induced dissociation of the immune-complex by which bound peptide ions are released. When analyzing a peptide mixture, measuring the mass of the complex-released peptide ions identifies which of the peptides contains the epitope. A step-wise increase in the collision cell voltage difference changes the intensity ratios of the surviving immune complex ions, the released peptide ions, and the antibody ions. From all the ions´ normalized intensity ratios are deduced the thermodynamic quasi equilibrium dissociation constants (KDm0g#) from which are calculated the apparent gas phase Gibbs energies of activation over temperature (ΔGm0g#T). The order of the apparent gas phase dissociation constants of four antibody – epitope peptide pairs matched well with those obtained from in-solution measurements. The determined gas phase values for antibody affinities are independent from the source of the investigated peptides and from the applied instrument. Data are available via ProteomeXchange with identifier PXD016024. SignificanceITEM - TWO enables rapid epitope mapping and determination of apparent dissociation energies of immune complexes with minimal in-solution handling. Mixing of antibody and antigen peptide solutions initiates immune complex formation in solution. Epitope binding strengths are determined in the gas phase after electrospraying the antibody / antigen peptide mixtures and mass spectrometric analysis of immune complexes under different collision induced dissociation conditions. Since the order of binding strengths in the gas phase is the same as that in solution, ITEM – TWO characterizes two most important antibody properties, specificity and affinity.

Thermodynamic Quasi-Equilibrium Model for the Energetic Performances Analysis of the Air and Air–Steam Gasification of Raw and Pretreated Cotton Stalks by Torrefaction and Carbonization

Numerical and experimental study of the gasification of raw and pretreated (torrefied and carbonized) cotton stalks were investigated. The experimental results were used to calibrate the quasi-equilibrium model by multiplying the equilibrium reaction constant with coefficient varying from 0.01 to 10 and by fixing the methane molar fraction. Values varying from 0.15 to 0.7, 0 to 0.8 and 400 to 900 K were considered for air equivalence ratio (ER), the ratio of steam to fuel (SF) and the temperature of steam respectively. LHV and energy efficiency decreased from 4528 kJ Nm− 3 and 73.5% for the raw cotton stalks to 3984 kJ Nm− 3 and 68.9% for torrefied cotton stalks and to 3815 kJ Nm− 3 and 69.6% for carbonized cotton stalks. The energy efficiency was improved by steam injection to 80, 78 and 75% for the gasification of raw, torrefied and carbonized CS respectively due to the increase of H2 and CH4. The air–steam gasification was more efficient to air gasification at a temperature of steam over than 500 K for raw cotton stalks. However, only the air–steam gasification of pretreated cotton stalks was recommended since it has the net energy efficiency (which consider the steam energy) superior to 60%.

Dynamics of induced glass transition of porous and nonporous silica nanoparticles

The present paper reports induced glass transition dynamics appeared in porous silica (PSi) and nonporous silica (NPSi) nanoparticles. The size of these spherical particles is 5–15 nm for PSi and 15–20 nm for NPSi. PSi shows two glass transitions (Tg1 and Tg2) on heating, whereas NPSi shows one glass transition (Tg). The NPSi shows Tg at a higher temperature than PSi. PSi shows an exothermic transition on cooling, whereas NPSi shows no transition on cooling. Both Tgs appeared in PSi show dynamic behavior with the existence of positive activation energy. Both Tgs are reversible in PSi, whereas NPSi shows only one and irreversible Tg. The observed glass transitions in PSi and NPSi follow the configuron percolation model and show thermodynamic quasi-equilibrium with percolation threshold (fc) <1. The silica nanoparticles show induced glass transitions because of the presence of weak hydrogen bonds (HB) and a weak van der Waal force present in PSi, whereas the lack of porosity in NPSi shows irreversible Tg with stronger HB. The porosity of PSi makes it more reactive and dynamic due to its capillary behavior and shows its applicability in medical sciences, whereas the stability of NPSi makes it important for industrial research.

Thermodynamic origin of the slow free exciton photoluminescence rise in GaAs

We use time-resolved photoluminescence (TRPL) spectroscopy to unequivocally clarify the microscopic origin of the nanosecond free exciton photoluminescence rise in GaAs at low temperatures. In crucial distinction from previous work, we examine the TRPL of the GaAs free exciton second LO-phonon replica. This enables us to simultaneously monitor the unambiguous time evolution of the total exciton population and the cooling dynamics of the initially hot free exciton ensemble. We demonstrate by a model based on the Saha equation and the experimentally determined cooling behavior that the long-debated slow photoluminescence rise is caused by time-dependent shifts in the thermodynamic quasiequilibrium between free excitons and the uncorrelated electron-hole plasma.

Spontaneous emission of electromagnetic radiation in turbulent plasmas

Known radiation emission mechanisms in plasmas include bremmstrahlung (or free-free emission), gyro- and synchrotron radiation, cyclotron maser, and plasma emission. For unmagnetized plasmas, only bremmstrahlung and plasma emissions are viable. Of these, bremmstrahlung becomes inoperative in the absence of collisions, and the plasma emission requires the presence of electron beam, followed by various scattering and conversion processes. The present Letter proposes a new type of radiation emission process for plasmas in a state of thermodynamic quasi-equilibrium between particles and enhanced Langmuir turbulence. The radiation emission mechanism proposed in the present Letter is not predicted by the linear theory of thermal plasmas, but it relies on nonlinear wave-particle resonance processes. The electromagnetic particle-in-cell numerical simulation supports the new mechanism.

Mechanisms of Protein Binding to DNA: Statistical Interactions are Important

Protein molecules binding to DNA initiate sequences of biochemical transitions that control and regulate all major processes in living cells (1). It has long been understood that the efficient transfer of genetic information is possible when genome-regulating protein molecules are found to be strongly bound to special sequences on DNA, known as specific binding sites. It was later realized that finding these target sequences might be complicated by the existence of a large number (≃106–109 per DNA) of other nonspecific binding sites and because of low concentrations of relevant protein molecules (2–4). Although significant experimental and theoretical efforts to investigate mechanisms of protein binding to DNA have been made, the role and functioning of nonspecific interactions has not been fully understood.

Queue Performance in Presence of Long-Range Dependencies – an Empirical Study

The queuing, as an inherent feature of each real system, plays a very important role in teletraffic networks as well. It is known that the queuing system consists of three basic components: the input stream of requests, the service processes and the queue discipline. The optimal performance of system can be achieved only in the case when all components are “matched” together. The teletraffic models that describe the early telephone services (e.g. Poisson and Markov) have been very successful. One of the main reasons for this success with models, which accurately resembles the real-world behavior, has been due to the highly static, low varying nature of early development phase of telephone voice traffic. This means that the whole environment of early telephone networks can be treated as a simple system. The main features of such systems can be described by: thermodynamic quasi-equilibrium, homogenous topologies, random graph theory, short-range dependencies, Poisson distribution, circuit switching, etc. However, the evolution of teletraffic from voice to new data traffic and integrated services inevitably leads to the vastly different statistical characteristics that are much more irregular and variable and as a result undermine the basis for the traditional traffic models. In this paper we show that taking into account the complex systems approach the existence of long-range dependencies (expressed by 1/f noise) influence queue performance. This is done basing on analytical approach with presentation of long-range dependent queue model and also by experimental study of traffic behavior in computer network during daily workload generated by computer user.

Multiparticle clusters and carbon superstructure in martensite

On the basis of experimentally verified concentration expansion tensor values, stress induced two-particle C-C potentials have been calculated in harmonic approximation. A calculation method has been developed and expressions derived for the evaluation of multiparticle interaction potentials and cluster population. The temperature range of the applicability of the method has been estimated. On the basis of this method it has been demonstrated that in thermodynamic quasi-equilibrium, carbon atoms exist in clustered form. The clusters most frequently appearing at 300 K are of four- and five-particle type. The cluster configurations have been determined and the binding energy per atom has been estimated as about 0.5 eV. At 78 K, there exist practically only five-particle linear clusters situated along the tetragonal C axis. It has been postulated that a superstructure may exist in martensite with a binding energy per atom nearly four times higher than in the case of the above clusters. The presence of superstructure is associated with the formation of five-atom seeds in the form of pyramids having their basis in the (001) plane. The formation of seeds with different topology from the other clusters is associated with overcoming a potential barrier. The postulated form of ordering at low temperatures should exhibit high thermal stability with respect to ordering changes and order-disorder phase transitions, as well as to carbide formation.

Contact etching of GaP substrates by GaInPAs saturated solution during liquid phase heteroepitaxy

The results of a theoretical and experimental analysis of isothermal contact etching of GaP substrate by Ga-In-P-As saturated solution are presented. Using the model of interatomic interaction at the interface during isothermal exposure of liquid and solid phases, conditions for thermodynamic quasiequilibrium of the above system are determined. Considering mass balance for the conditions of coherent lattice deformation of the interface, the amount of contact etching of GaP substrate during typical conditions of liquid phase heteroepitaxy of GaxIn1−xPyAs1−y layers is quantitatively determined.

A model of internal lattice deformation of the interface during liquid phase heteroepitaxy of AxB1–xCyD1–y-type AIIIBV compounds

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Thermodynamics of excitons in coupled quantum wells

Because of their long lifetime in coupled quantum wells under an applied electric field, excitons may he able to reach thermodynamic quasi-equilibrium. Here we measure photoluminescencc and photoluminescence excitation spectra from a symmetric coupled double quantum well. Analysis of the spectra shows that thermodynamic quasi-equilibrium is not achieved at temperatures below 6 K, where the excitons are trapped in a metastahle distribution. At higher temperatures, quasi-equilihrium is achieved. Because of strong repulsion between the excitons, the quasi-equilihrium distribution can he modeled with a Fermi-Dirac distribution. The model quantitatively explains the striking temperature dependence of the photoluminescence lincwidth which has been previously reported.

Thermodynamic analysis of the chemical vapor deposition of diamond films

The chemical vapor deposition of carbon films is analyzed using the thermodynamic quasiequilibrium model and a phase diagram for the carbon-hydrogen system is obtained. When the enhanced etching of graphite by hydrogen is included in the model, a region in the phase diagram where diamond is the only stable solid phase of carbon is predicted, consistent with the experimental results of S. Matsumoto, Y. Sato, M. Tsutsumi and N. Setaka [ J. Mater. Sci. 17, 3106 (1982)]. It is further predicted that higher carbon fractions (at least 5%) in the gas phase will be required for deposition of diamond at atmospheric pressure.