Precursor Candidates Research Articles

Reply to Comment on “Preseismic lithosphere‐atmosphere‐ionosphere coupling”

A number of electromagnetic candidates of earthquake precursors have been reported, but Rodger and Clilverd (Comment on “Preseismic Lithosphere‐Atmosphere‐Ionosphere Coupling,” Eos, this issue) comment that their statistical significance has not been verified. Since most of the proposed mechanisms of reported earthquake precursors are controversial, it is true that the first requisite for verification should mainly rely on statistical analysis, as these authors rightly point out. The statistical analysis, in fact, is exactly what concerned researchers are continuously challenging. It is a difficult goal largely because of the limited number of large earthquakes.In an Eos article [Kamogawa, 2006], some recent promising results that had been statistically studied were reviewed. Pioneering works by Gokhberg et al. [1989] and Molchanov and Hayakawa [1998] were also mentioned even if they were lacking in elaborate statistical analysis. In their comment, Rodger and Clilverd stress that the existence of preseismic subionospheric anomalies is controversial, citing some papers such as those by Michael [1996] and Clilverd et al. [1999]. Although I did not refer to these papers due to the space limitation of the Eos article, I agree with their point.

Determination of the elemental composition of trace analytes in complex matrices using exact masses of product ions and corresponding neutral losses

The emergence of time-of-flight (TOF) and hybrid quadrupole/time-of-flight (Q-TOF) mass spectrometers has offered new possibilities for determining the elemental composition of analytes present at trace levels. The mass accuracy provided by these instruments is currently in the range of 2-5 m m/z units, permitting the determination of the elemental composition of small molecules. The orthogonal information of relative isotopic abundances (RIAs) is used to reduce the number of elemental compositions that are possible, based on consideration of exact masses. Elimination of additional possible compositions has been reported when the analyte is fragmented and its resulting product ions and corresponding neutral losses are carefully analyzed. Published algorithms reduce the number of proposed precursor ions by deleting each precursor candidate which cannot be explained by summing any combination of postulated product ion and corresponding neutral loss elemental composition candidates. An extension of such algorithms is described in this paper. This approach compares not only the precursor ion with the different fragments, but tests the possible descent of any ion from all other recorded ions. This extended algorithm has been tested by processing published data. Algorithms analyzing product ion spectra can be used for real-life data. However, there is a risk that an ion which originates from the mobile phase or from a co-eluting matrix compound can be mathematically correlated to the investigated precursor ion. Such an incorrect correlation can lead to the deletion of a correct elemental composition. This is an important issue if TOF rather than Q-TOF instruments are used. Therefore, ultra-performance liquid chromatography (UPLC) and a peak deconvolution algorithm were used to generate and process TOF chromatograms in order to minimize the number of ions which are not related to the analyte precursor ion. The combined use of chromatographic deconvolution and product ion spectra has been tested and is critically discussed.

Formation of flame ions, clusters, nanotubes, and soot in hydrocarbon flames

The actual work deals with the present state of research on flame ions, polyaromatic hydrocarbons, nanotubes, fullerenes, and soot particles in premixed flames. Experimental arrangements for detection and quantitative investigation of flame ions are presented. In addition, the influence of ions on flame chemistry and on formation of carbon particles under non-sooting and sooting conditions is discussed. The study also focuses on the formation pathway from flat polyatomic hydrocarbons to fullerenes, nanotubes, and soot particles. In this connection, the features of arched “aromers,” which are high reactive metastable species and leading candidates for soot precursors and fullerene formation, are reported. These aromers seem to be a kind of “switch” capable of producing either fullerenes or soot particles, depending on the reaction conditions. At lower flame temperatures and a high number density of small unsaturated hydrocarbons, bimolecular reactions are favored, and the formation of soot particles exceeds that of fullerenes. It is also shown how the further growth of soot particles can be described, namely, by soot mass growth and by coagulation processes in strong sooting flames. Typical values for soot volume fractions and particle diameters under various reaction conditions are given.

Ammonia cores in high mass star formation regions

We observed a sample of 35 water masers not coincident with known HII regions and/or low mass young stellar objects (YSOs) with the Effelsberg 100 m telescope in the NH3(J,K) = (1,1), (2,2), (3,3) and (4,4) transitions. Sixteen sources were detected in the NH3 emission. The detection rate is 46%. All these sixteen sources have NH3 (1,1) and (2,2) emission, among which four sources have NH3 (3,3) emission. Comparing with the IRAS and the 2MASS data, we analyzed the relationship between the detection rate and the infrared color, the dust temperature and the source distance. All the detected sources were mapped and 17 cores were obtained (one source IRAS 20215+3725 has two cores). From the detected sources five cores do not coincide with radio continuum or IRAS and MSX point sources. Excluding one core that has no MSX data available, the remaining eleven cores are coincident with IRAS or MSX point sources. The typical size and mass of the cores are 1.6 pc and 1.5 x 10(3) M-circle dot, respectively. The average line widths of the NH3 (1,1) and (2,2) are 1.54 and 1.73 km s(-1). The average kinetic temperature of the gas is about 19 K. These values are much larger than those of low mass cores. The NH3 cores that coincide with IRAS sources (referred to as Group I) have slightly larger line widths (1.65 and 1.75 km s(-1) for the (1,1) and (2,2) lines, respectively) and larger masses (1.8 x 10(3) M-circle dot) than the mean values of the sample. For this type of core the kinetic temperature correlates with the line width. The line width appears to correlate with the bolometric luminosity and the core size. Despite the average luminosity of 2.9 x 10(4) L-circle dot, there is no detectable 6 cm emission. These are candidates for high mass protostars or precursors of UC HII regions. The NH3 cores with peaks onset from infrared sources (referred to as Group II) have an average size of 1.7 pc and an average line width of 1.50 km s(-1) for the (1,1) line. The line width of the (1,1) emission is smaller than that of the group I. The average mass is 9.4 x 10(2) M-circle dot. One possible explanation for the deviation is that the NH3 peak and the infrared source correspond to different clumps. These cores are potential high mass star formation sites and may be at an earlier evolutionary stage than those with IRAS point sources. This type of core is seen in mapping observations, and can be easily missed by single-spectrum observations toward the IRAS position.

Water in the Early Earth

The origin of water is a long standing problem that has fascinated generations of philosophers and scientists since the dawn of humanity. It has to do with processes that took place in the nascent solar system, but, unfortunately, we lack record of what really happened during this dark age. On Earth, the tectonic activity has erased completely any record dating back from this period, and the oldest rocks preserved on Earth crystallized about 600 Ma after start of solar system condensation (ASSC). What we observe today does not represent necessarily what was present when the solar system formed, and it may well be possible that the true water ancestors could have had chemical and isotopic characteristics that are not observed in any reservoir of the present-day solar system. However, the extraterrestrial objects that escaped planetary differentiation (chondrites, comets, interplanetary dust) are probably the best available precursor candidates for the source of volatile elements in Earth. In this context, the nature of such potential contributions can be estimated in view of chemical and isotopic mass balance, taking into account astrophysical and/or thermodynamic constraints on planetary system formation. The Earth is not a water-rich body. Water at the Earth’s surface (1.5 × 1024 g), mostly in the oceans, makes about 0.025% H2O over the whole Earth (5.97 × 1027 g). Most estimates for the mantle water content advocate a few ocean masses, so that the bulk water content of Earth may be <0.2% H2O (see the “Potential Water Contributors” section in this chapter). For comparison, carbonaceous chondrites contain up to 10% equivalent water (Boato 1954; Robert and Epstein 1982; Kerridge 1985) and comets have up to 50% H2O (Delsemme 1988). Thus the contribution of only a small fraction of such water-rich bodies …

Computational Prediction of MicroRNAs Encoded in Viral and Other Genomes

We present an overview of selected computational methods for microRNA prediction. It is especially aimed at viral miRNA detection. As the number of microRNAs increases and the range of genomes encoding miRNAs expands, it seems that these small regulators have a more important role than has been previously thought. Most microRNAs have been detected by cloning and Northern blotting, but experimental methods are biased towards abundant microRNAs as well as being time-consuming. Computational detection methods must therefore be refined to serve as a faster, better, and more affordable method for microRNA detection. We also present data from a small study investigating the problems of computational miRNA prediction. Our findings suggest that the prediction of microRNA precursor candidates is fairly easy, while excluding false positives as well as exact prediction of the mature microRNA is hard. Finally, we discuss possible improvements to computational microRNA detection.

Volatile CVD precursor for Ni film: cyclopentadienylallylnickel

We utilized cyclopentadienylallylnickel, CpAllylNi, as a precursor for chemical vapor deposition (CVD). CpAllylNi is a liquid at 10 °C, and it has a high vapor pressure, 10 Torr at 73 °C. Thermal gravimetry differential thermal analysis indicated that the decomposition occurred slightly below 200 °C. CpAllylNi decomposed, generating several gases, of which content was more than those of other cyclopentadienyl Ni precursors. In a CVD CpAllylNi/H 2 gas supply system, the other cyclopentadienyl Ni precursor characteristics contributed to a high deposition rate with low residual carbon at low temperature, 13 nm/min, 4% carbon, and 120 °C, respectively. The low temperature was caused by interactions of CpAllylNi and H 2. CpAllylNi was superior to MeCp 2Ni with respect to volatility and leaving residual carbon in the deposited film. Therefore, CpAllylNi is one of the best precursor candidates for depositing Ni thin films with low carbon impurity by low-pressure CVD.

Similarities between the clathrasils DOH, DDR, MEP and MTN

AbstractClathrasils are porous framework silicates with cage-like voids. Structural similarities between the clathrasilsDOH,MTN,MEP, DD3H andDDRhave been analyzed in the context of host/guest interaction and crystallization mechanism. A building unit consisting of 30 T atoms is used as common structural feature to give an alternative description of the well-known layers of [512]-cages. The [512]-layers, or Periodic Building Units (PerBU’s), are constructed from two 12-rings connected through a common 6-ring to form two half cages or a 12-ring double cup. These ‘half-cages’ are essentially the bottom of the large ‘inter-layer’ cages in the clathrasils. The rigorous derivation of all possible framework types and their cages based on these principles shows the richness of the concept and makes possible new strategies for the synthesis. The ‘half-cages’ are also possible candidates for precursors which might exist in solution in close contact with templating guest species initiating the nucleation of the crystals.

Piezo stimulated currents in marble samples: precursory and concurrent-with-failure signals

Abstract. The Earth’s electric field transient variations are promising candidates of earthquake precursors. In order to study the physical mechanisms of such precursory signals, laboratory experiments of uniaxial compression were carried out. More specifically the behaviour of stressed marble samples from Penteli Mountain was investigated. The samples were subjected to a time-varying uniaxial compression at both variable and constant stress rates. During the first set of experiments weak electric currents were detected during pressure variations. Such Piezo Stimulated Currents (PSC) were detected while stress steps, both positive and negative were applied, the maximum stress never being greater than the elasticity limit. During the second set of experiments stress was applied at a constant rate starting from zero-stress and ending in fracture. In the region beyond the elastic limit a PSC was detected which after reaching a peak suffered a reversal in its polarity just before fracture. In a third set of experiments the same procedure was applied to previously structurally damaged samples taking care not to fracture them. In all cases the PSC followed the variation of stress and moreover it was observed that a linear relationship existed between the PSC maxima and the corresponding stress-rate maxima. The mechanism responsible for the described phenomena can be ascribed to the Moving Charged Dislocations model.

Inexpensive set-up for determination of decomposition temperature for volatile compounds

The utility of precursors for atomic layer chemical vapour deposition (ALCVD) growth is limited by the sublimation and decomposition temperatures. Sublimation temperatures are conveniently obtained by thermogravimetry (TG) under vacuum. We present here a relatively inexpensive method to obtain information about the decomposition temperature for a precursor candidate for ALCVD. This approach requires an oven with a controlled temperature gradient and a long ampoule for each precursor. The precursors tested in this work comprise the thd complexes (Hthd=2,2,6,6-tetramethylheptane-3,5-dione) of V, Cr, Mn, Fe, Co, Ni, Cu, Zn, La, and Ca.

HfO2 Gate Dielectrics Deposited via Tetrakis Diethylamido Hafnium

films deposited via tetrakis diethylamido hafnium (TDEAH) precursor using MOCVD (metal organic chemical vapor deposition) are presented. TDEAH is a promising precursor candidate for the deposition of high permittivity gate dielectrics. We report the impact of process and annealing conditions on the physical and electrical properties of the film. Deposition and annealing temperatures influence the microstructure, density, and impurity levels of TDEAH films. Spectroscopic ellipsometry shows that film microstructure manifests itself in the optical properties of the film, particularly in the presence of a band edge related feature at 5.8 eV. An impurity analysis using Auger electron spectroscopy, secondary ion mass spectroscopy, and Raman spectroscopy, indicates that carbon impurities from the precursor exist as clusters within the dielectric. The impact of deposition temperature and annealing temperature on the capacitance vs. voltage and current density vs. voltage characteristics of platinum gated capacitors is studied. Correlation of physical film properties with the capacitance and leakage behavior of the TDEAH films indicates that impurities, in the form of carbon clusters, and low film density are detrimental to the electrical performance of the gate dielectric. © 2003 The Electrochemical Society. All rights reserved.

Acrylamide in food: mechanisms of formation and influencing factors during heating of foods

Background: In April 2002, the Swedish National Food Administration and a scientific group at the University of Stockholm jointly announced that they had shown acrylamide to be formed during the preparation of food and found it to occur in many foodstuffs. These new findings were clearly of concern to many types of industrial food processing as well as to home cooking. The Swedish Food Federation (Li) initiated and financed the formation of an expert committee to look into the chemical mechanisms. The present review is the final report of that expert committee. Design: The study identified, examined and put together facts and present knowledge on reaction routes for acrylamide formation in food and causal connections to cooking and food processing conditions. The results are based on literature surveys, examination of the analytical data published by the Swedish National Food Administration and other follow-up studies, contacts with international scientific networ ks, and observations from food companies. Results: The exact chemical mechanism(s) for acrylamide formation in heated foods is unknown. Several plausible mechanistic routes may be suggested, involving reactions of carbohydrates, proteins/amino acids, lipids and probably also other food components as precursors. With the data and knowledge available today it is not possible to point out any specific routes, or to exclude any possibilities. It is likely that a multitude of reaction mechanisms is involved. Acrolein is one strong precursor candidate, the origin of which could be lipids, carbohydrates or proteins/amino acids. Acrylamide is a reactive molecule and it can readily react with various other components in the food. The actual acrylamide level in a specific food product, therefore, probably reflects the balance between ease of formation and potential for further reactions in that food matrix. There are indications in support of that the Maillard reaction being an import a nt reaction route for acrylamide formation, but lipid degradation pathways to the formation of acrolein should also be considered. Conclusions: Reliable analytical methods to measure acrylamide in foods are available. Model studies are needed to identify precursors and reaction route(s) based on current hypotheses and to elucidate possible further reactions between acrylamide and other food components. Studies are needed to optimize formulation and processing conditions to minimize acrylamide levels, taking other product quality properties into consideration. Keywords: Acrylamide, cooking, food processing, heated foods, Maillard reaction.

Synthesis and structures of zirconium amide-iodide complexes.

Zirconium amide-iodide complexes were synthesized for possible use as chemical vapor deposition precursors to zirconium nitride films. The series of six complexes Zr(NR(2))(4-n)I(n)(R = Me or Et; n = 1-3) was prepared by reacting ZrI(4) and Zr(NR(2))(4) in hot toluene. X-ray crystallographic analyses were performed for Zr(NMe(2))(3)I, Zr(NEt(2))(2)I(2), and Zr(NEt(2))I(3). In the solid state, Zr(NMe(2))(3)I and Zr(NEt(2))(2)I(2) are the discrete dimers [Zr(NMe(2))(2)I(mu-NMe(2))](2) and [Zr(NEt(2))(2)I(mu-I)](2), and Zr(NEt(2))I(3) is the polymer of dimers ([Zr(NEt(2))I(2)(mu-I)](2))(n). In solution, Zr(NEt(2))(3)I is proposed to be monomeric on the basis of NMR data and a molecular weight determination. The complex Zr(NEt(2))(3)I is the most promising precursor candidate because of its physical properties.

Synthesis and structures of aluminum alkanethiolate complexes.

The homoleptic aluminum thiolate complex [Al(mu-S-t-Bu)(S-t-Bu)(2)](2) was prepared by reacting AlBr(3) with NaS-t-Bu while the analogous 2-propanethiolate complex [Al(mu-S-i-Pr)(S-i-Pr)(2)](2) was synthesized by reacting AlH(3)(OEt(2)) with i-PrSH. In the solid state, the dimers have tetrahedral Al atoms and anti-Al(mu-SR)(2)Al four-member rings. The attempted synthesis of [Al(mu-S-t-Bu)(S-t-Bu)(2)](2) by reacting Al(N-i-Pr(2))(3) with t-BuSH in THF solvent yielded the thermally stable THF adduct Al(S-t-Bu)(3)(THF). The same reaction in diethyl ether solvent produced a mixture of [Al(mu-mgr;-S-t-Bu)(S-t-Bu)(2)](2) and the salt [i-Pr(2)NH(2)][Al(S-t-Bu)(4)]. In the solid-state structure of the salt, the anion [Al(S-t-Bu)(4)](-) has a distorted tetrahedral geometry. Reactions of [Al(NMe(2))(3)](2) and AlH(3)(NMe(2)Et) with the alkanethiols yielded stable amine adducts Al(SR)(3)(R'NMe(2)) (R = i-Pr or t-Bu; R' = H or Et). The ligand adducts Al(S-i-Pr)(3)(HNMe(2)) and Al(S-t-Bu)(3)(THF) have distorted trigonal pyramidal geometries in the solid state. Three of the new compounds, [Al(mu-S-i-Pr)(S-i-Pr)(2)](2) and Al(SR)(3)(HNMe(2)) (R = i-Pr or t-Bu), are viable precursor candidates for the chemical vapor deposition of aluminum sulfide films because they are thermally stable, volatile liquids at moderate temperatures.

Molecular and isotopic analyses of Tagish Lake alkyl dicarboxylic acids

Abstract— The Tagish Lake meteorite soluble organic suite has a general composition that differs from those of both CI and CM chondrites. These differences suggest that distinct processes may have been involved in the formation of different groups of organics in meteorites. Tagish Lake alkyl dicarboxylic acids have a varied, abundant distribution and are, with carboxylated pyridines, the only compounds to have an occurrence comparable to that of the Murchison meteorite. This study has undertaken their molecular and isotopic characterization, with the aim to understand their origin and to gain insights into the evolutionary history of the meteorite parent body.Tagish Lake alkyl dicarboxylic acids are present as a homologous series of saturated and unsaturated species with three‐ through ten‐carbon atom chain length. Linear saturated acids are predominant and show decreasing amounts with increasing chain length. A total of 44 of these compounds were detected with the most abundant, succinic acid, present at ˜40 nmol/g meteorite. Overall the molecular distribution of Tagish Lake dicarboxylic acids shows a remarkable compound‐to‐compound correspondence with those observed in the Murchison and Murray meteorites. In both Tagish Lake and Murchison, the imides of the more abundant dicarboxylic acids were also observed.The hydrogen and carbon isotopic compositions of individual Tagish Lake dicarboxylic acids were determined and compared to those of the corresponding acids in the Murchison meteorite. All δD and δ13C values for Tagish Lake acids are positive and show a substantial isotopic enrichment. δD values vary from, approximately, +1120%o for succinic acid to +1530%o for methyl glutaric acid. δ13C values ranged from +12.6%o for methyl glutaric acid to +22.9%o for glutaric acid, with adipic acid having a significantly lower value (+5.5%o). Murchison dicarboxylic acid showed similar isotopic values: their δ513C values were generally higher by an average 17% and δD values were lower for succinic and glutaric acids, possibly due to contamination.The molecular and isotopic data collected for these compounds restrict their possible origin to processes, either interstellar or of very cold nebular regions, that produced significant isotopic enrichments. Saturated or partially unsaturated nitriles and dinitriles appear to be good precursor candidates as their hydrolysis, upon water exposure, would produce dicarboxylic acids and other carboxylated species found in Tagish Lake. This evolutionary course could possibly include pre‐accretionary processes.

Massive Star Formation: New Results

In the past year several new observations with important implications for massive star formation (MSF) have been obtained. Among these were the detection of UC HII region precursor candidates at 350µm and the discovery of many hard X-ray point sources in the Orion and W3 MSF regions. These observations are summarized below.Hunter et al. (1998, 2000) imaged 25 MSF regions at 350µm to search for candidate precursors of UC HII regions (i.e. luminous submm/FIR emission, maser sources, and no HII emission). Of the 28 sources detected, 10 appear to be UC HII precursor candidates.

Acrylamide in food: mechanisms of formation and influencing factors during heating of foods

Background: In April 2002, the Swedish National Food Administration and a scientific group at the University of Stockholm jointly announced that they had shown acrylamide to be formed during the preparation of food and found it to occur in many foodstuffs. These new findings were clearly of concern to many types of industrial food processing as well as to home cooking. The Swedish Food Federation (Li) initiated and financed the formation of an expert committee to look into the chemical mechanisms. The present review is the final report of that expert committee. Design: The study identified, examined and put together facts and present knowledge on reaction routes for acrylamide formation in food and causal connections to cooking and food processing conditions. The results are based on literature surveys, examination of the analytical data published by the Swedish National Food Administration and other follow-up studies, contacts with international scientific networ ks, and observations from food companies. Results: The exact chemical mechanism(s) for acrylamide formation in heated foods is unknown. Several plausible mechanistic routes may be suggested, involving reactions of carbohydrates, proteins/amino acids, lipids and probably also other food components as precursors. With the data and knowledge available today it is not possible to point out any specific routes, or to exclude any possibilities. It is likely that a multitude of reaction mechanisms is involved. Acrolein is one strong precursor candidate, the origin of which could be lipids, carbohydrates or proteins/amino acids. Acrylamide is a reactive molecule and it can readily react with various other components in the food. The actual acrylamide level in a specific food product, therefore, probably reflects the balance between ease of formation and potential for further reactions in that food matrix. There are indications in support of that the Maillard reaction being an import a nt reaction route for acrylamide formation, but lipid degradation pathways to the formation of acrolein should also be considered. Conclusions: Reliable analytical methods to measure acrylamide in foods are available. Model studies are needed to identify precursors and reaction route(s) based on current hypotheses and to elucidate possible further reactions between acrylamide and other food components. Studies are needed to optimize formulation and processing conditions to minimize acrylamide levels, taking other product quality properties into consideration. Keywords: Acrylamide, cooking, food processing, heated foods, Maillard reaction.

Developmental Pathways of Children With and Without Familial Risk for Dyslexia During the First Years of Life

Comparisons of the developmental pathways of the first 5 years of life for children with (N = 107) and without (N = 93) familial risk for dyslexia observed in the Jyvaskyla Longitudinal study of Dyslexia are reviewed. The earliest differences between groups were found at the ages of a few days and at 6 months in brain event-related potential responses to speech sounds and in head-turn responses (at 6 months), conditioned to reflect categorical perception of speech stimuli. The development of vocalization and motor behavior, based on parental report of the time of reaching significant milestones, or the growth of vocabulary (using the MacArthur Communicative Development Inventories) failed to reveal differences before age 2. Similarly, no group differences were found in cognitive and language development assessed by the Bayley Scales of Infant Development and the Reynell Developmental Language Scales before age 2.5. The earliest language measure that showed lower scores among the at-risk group was maximum sentence length at age 2. Early gross motor development had higher correlation to later language skills among the at-risk group rather than the control children. The most consistent predictor of differential development between groups was the onset of talking. Children who were identified as late talkers at age 2 were still delayed at the age 3.5 in most features of language-related skills-but only if they belonged to the group at familial risk for dyslexia. Several phonological and naming measures known to correlate with reading from preschool age differentiated the groups consistently from age 3.5. Our findings imply that a marked proportion of children at familial risk for dyslexia follow atypical neurodevelopmental paths. The signs listed previously comprise a pool of candidates for early predictors and precursors of dyslexia, which await validation.

In vivo maturation and migration of dendritic cells.

The hallmark of immunity is antigen (Ag) recognition. From early life until death we face countless Ags; many are deleterious and come from the outside world. However, lymphocytes, the mediators of specific acquired immunity, are usually not exposed where foreign antigens are encountered. Thus a system must ferry these Ags from the periphery into inner tissues where lymphocytes comfortably reside or traffic. Clearly, translocating Ags from the periphery to the lymphoid niches is a pivotal function whereby the dendritic cell (DC) system initiates immune responses. DCs, however, are not passive Ag couriers; a dynamic process not fully understood is triggered by Ag deposition. Strategically poised at the boundaries between the inner and the outside world, in a way bridging innate and acquired immunity, DCs sample, trap, engulf, and digest Ags of very diverse origin, in what is called Ag processing. Antigenic fragments are then regurgitated, exposed at the cell surface through one of three molecular pathways [Major histocompatibility complex (MHC) CI and CII, and CD1)] responsible for an efficacious Ag presentation. Concomitantly, DC bear an arsenal of powerful costimulatory molecules [CD40; CD80; CD86; DC-specific/intercellular adhesion molecule type 3-grabbing, non-integrin (DC-SIGN)] and the potential to produce critical cytokines [chemokines, interleukin-12 (IL-12), etc.], thus ensuring the initiation and the fate of acquired immunity. The DC system is particularly efficient, not just translocating, but also transforming antigens sampled at the earlier local milieu into an immunologically accesible language, becoming an excellent reporter of the previous antigenic past, translating the conundrum posed by viruses, bacteria, proteins, etc., into T-cell receptor (TCR) ligands; a short-peptide vocabulary that T cells especially now understand. A highly dynamic process is thus triggered by encountering Ags; while these are carried and processed to be appropriately presented, DCs in turn experience a variety of changes: migratory, phenotypical, functional; all encompassed in the term maturation. Essentially, DC maturation means to change from an antigen-capturing to an antigen-presenting, T-cell-priming mode, a process whereby DCs convert antigens into efficacious immunogens, express the necessary cytokines and costimulatory molecules, thus appropriately initiating the specific, acquired clonal immunity.

A theoretical approach to the single-source precursor concept: quantum chemical modeling of gas-phase reactions

Results of extensive quantum-chemical modeling of the gas-phase reactions during CVD of group 13–15 materials are discussed in the light of single-source precursor concept. Two quantitative parameters (donor–acceptor bond dissociation enthalpy and elimination reaction enthalpy) are introduced as criteria for the classification of potential candidates for the single-source precursors. Hydrogen-containing molecules are predicted to have higher importance as precursors for the stoichiometry-controlled CVD processes. Importance of the ring and cluster single-source precursors in the CVD of doped metal nitrides is emphasized. In contrast, P, As-containing precursors with metal-halide bonds are predicted to be inefficient.