Absolute Metal Research Articles

One on one with Carolyn L. Ladd

After completing their PhD at the University of Montreal and a postdoc at the California Institute of Technology, Carolyn L. Ladd began working for Dow, developing sustainable technologies to reduce the carbon footprint of industrial processes. Kirstin S. Bode spoke with them about Ladd’s career path and queer activism. This interview has been edited for length and clarity. Kirstin S. Bode: Can you tell me a little bit about the research you did for your PhD? Carolyn L. Ladd: For my PhD, I worked for André Charette at the University of Montreal. I spent some time working on C–H activation, specifically of cyclopropanes, as well as asymmetric catalysis. I guess that’s when I first fell in love with homogeneous catalysis, and it also made me fall in love with palladium, my absolute favorite transition metal. That experience kind of just got me hooked into doing that type of work. KSB:

Direct Far-infrared Metal Abundances (FIRA). I. M101

Abstract Accurately determining gas-phase metal abundances within galaxies is critical as metals strongly affect the physics of the interstellar medium. To date, the vast majority of widely used gas-phase abundance indicators rely on emission from bright optical lines, whose emissivities are highly sensitive to the electron temperature. Alternatively, direct-abundance methods exist that measure the temperature of the emitting gas directly, though these methods usually require challenging observations of highly excited auroral lines. Low-lying far-infrared (FIR) fine structure lines are largely insensitive to electron temperature and thus provide an attractive alternative to optically derived abundances. Here, we introduce the far-infrared abundance (FIRA) project, which employs these FIR transitions, together with both radio free–free emission and hydrogen recombination lines, to derive direct, absolute gas-phase oxygen abundances. Our first target is M101, a nearby spiral galaxy with a relatively steep abundance gradient. Our results are consistent with the O++ electron temperatures and absolute oxygen abundances derived using optical direct-abundance methods by the CHemical Abundance Of Spirals (CHAOS) program, with a small difference (∼1.5σ) in the radial abundance gradients derived by the FIR/free–free-normalized versus CHAOS/direct-abundance techniques. This initial result demonstrates the validity of the FIRA methodology—with the promise of determining absolute metal abundances within dusty star-forming galaxies, both locally and at high redshift.

Formation and evolution of multistage ore-forming fluids in the Miocene Bangpu porphyry–skarn deposit, Southern Tibet: Insights from LA–ICP–MS trace elements of quartz and fluid inclusions

Abstract The large Bangpu Mo–Cu–Pb–Zn deposit, is a Mo-rich (~0.089%), Cu-poor (~0.32%) porphyry–skarn deposit located in the northeastern Gangdese porphyry copper belt (GPCB), Southern Tibet. In this study, LA–ICP–MS data for fluid inclusions and quartz formed during different stages of the mineralization are used to (1) constrain changes in fluid composition during mineralization; (2) infer the origin, transport pathways, and conditions of ore precipitation; and (3) explore the influence of magma chamber on fluid exsolution and shallow mineralization. The Cu content of the vapor-rich (VL) inclusions is higher than that of the halite-bearing (LVH) inclusions, while the Mo, Pb, and Zn contents of the VL and LVH inclusions are similar, indicating that Mo, Cu, Pb, and Zn had a common source, which is inferred to be the intermediate-level magma chamber. The metal contents of fluid inclusions in the early stage potassic alteration-related vein (A vein) and later stage sericitic alteration-related vein (B vein) are similar but variable, implying the intermediate-level magma chamber was too small to form a large stable fluid system. The enrichment of Mo, Pb, and Zn in the Bangpu deposit relative to other porphyry deposits in the GPCB is related to the participation of ancient crustal material. A comparison of our results with those from super-large porphyry Cu deposits elsewhere indicates that metal-rich fluids are not the sole factor to form ore deposits, and the variability of metal contents in the early exsolved fluids is a better predictor of mineralization potential than absolute metal concentrations.

Calibrating high resolution XRF core scanner data to obtain absolute metal concentrations in highly polluted marine deposits after two case studies off Portmán Bay and Barcelona, Spain.

X-ray fluorescence core scanners (XRF-CS) allow rapid, non-destructive, continuous and high-resolution analyses of the elemental composition of sediment cores, providing large sets of semi-quantitative data. These data can be converted to quantitative data through the linear regression approach using a relatively small number of discrete samples analyzed by techniques providing absolute concentrations. However, a precise characterization of the errors associated with the linear function is required to evaluate the quality of the calibrated element concentrations. Here we present a calibration of high-resolution XRF-CS for six metals (Ti, Mn, Fe, Zn, Pb and As) measured in heavily contaminated marine deposits so that absolute concentrations are obtained. In order to determine the best linear function for conversion of XRF data, we have tested three regression methods: the ordinary least-squares (OLS), which does not consider the standard error in any variable (x and y), the weighted ordinary least-squares (WOLS), which considers the weighted standard error of the vertical variable (y), and the weighted least-squares (WLS), which incorporates the standard error in both x and y variables. We demonstrate that the calibration method presented in this study significantly increases the correlation coefficient, higher than r2 = 0.94, and reduces both the data deviation and the errors of the linear function for the three regression methods. Nonetheless, the WLS appears as the best regression method to minimize errors in the calibrated element concentrations. Our results open the door to use calibrated XRF-CS data to evaluate marine sediment pollution according to the levels of the strictest sediment quality guidelines (SQG) with errors lower than 0.4%-2% for Fe, 1%-7% for Zn, 3-14% for Pb and 5%-16% for Mn. They highlight the robustness of the calibration procedure here presented for accurate and precise quantification of element concentrations from XRF-CS semi-quantitative data.

The Metal Content of Magmatic-Hydrothermal Fluids and Its Relationship to Mineralization Potential

Abstract A fundamental question in the study of magmatic-hydrothermal ore deposits is whether the mineralization potential of intrusions was already predetermined by the metal content of the exsolving fluids. The present study aims at addressing this question by reviewing the large number of microanalytical data (mostly laser-ablation ICP-MS data) obtained on fluid inclusions from this type of ore deposits over the last 20 years. Published data sets were screened for analyses of high-temperature fluid inclusions that are representative of premineralization fluids. A set of criteria was developed to distinguish such fluids from later, lower temperature fluids. In order to compensate differences in absolute metal concentrations caused by fluid immiscibility, all element concentrations were normalized to Na. A numerical model was developed to explore at which stage different metals are most efficiently extracted from a cooling pluton. The results suggest that the timing of most efficient metal extraction varies from metal to metal and strongly depends on pressure, the fluid/melt partition coefficient and the bulk mineral-melt partition coefficient. As a consequence, fluid compositions were chosen over the entire range of Cs/Na ratios recorded from a given pluton, as this ratio gives an indication of the fractionation degree of the silicate melts from which a fluid exsolved. In order to avoid bias toward occurrences from which a large amount of data are available, maximum four intermediate-density (ID)-type fluid inclusion assemblages plus four brines assemblages were chosen from each occurrence. Using the above-mentioned criteria, 169 fluid compositions from 12 Cu (Mo, Au) mineralized intrusions, 10 Sn/W mineralized intrusions, two Mo mineralized intrusions, and one U-Th-REE mineralized intrusion were finally chosen and plotted in graphs of X/Na versus Cs/Na. The results reveal that Sn- and Cu-mineralizing fluids contained more Sn and Cu, respectively, than the fluids analyzed from barren and Mo or U-Th REE mineralized intrusions. Positive correlations between fluid metal content and mineralization potential may exist also for W and REEs, whereas for Mo no such trend is evident. Therefore, at least for certain metals, the metal content of high-temperature fluid inclusions can be used as an indicator of the type and extent of mineralization. However, elevated metal concentrations are present also in some fluids from barren intrusions, which implies that the mineralization potential additionally depends on other factors such as the size of the intrusion and the development of structures that promote focused fluid flow.

Structural knowledge or X-ray damage? A case study on xylose isomerase illustrating both.

Xylose isomerase (XI) is an industrially important metalloprotein studied for decades. Its reaction mechanism has been postulated to involve movement of the catalytic metal cofactor to several different conformations. Here, a dose-dependent approach was used to investigate the radiation damage effects on XI and their potential influence on the reaction mechanism interpreted from the X-ray derived structures. Radiation damage is still one of the major challenges for X-ray diffraction experiments and causes both global and site-specific damage. In this study, consecutive high-resolution data sets from a single XI crystal from the same wedge were collected at 100 K and the progression of radiation damage was tracked over increasing dose (0.13-3.88 MGy). The catalytic metal and its surrounding amino acid environment experience a build-up of free radicals, and the results show radiation-damage-induced structural perturbations ranging from an absolute metal positional shift to specific residue motions in the active site. The apparent metal movement is an artefact of global damage and the resulting unit-cell expansion, but residue motion appears to be driven by the dose. Understanding and identifying radiation-induced damage is an important factor in accurately interpreting the biological conclusions being drawn.

The impact of species, respiration type, growth phase and genetic inventory on absolute metal content of intact bacterial cells.

Metal ions are abundant in microbial proteins and have structural, catalytic or electron-transferring roles. Metalloproteins are especially prevalent in respiratory chains where they couple electron flow with proton translocation across the membrane. Here, we explore the hypothesis that anaerobic respiratory chains can be investigated by quantitative whole-cell metallomics of the key metals Fe, Co, Ni and Mo. Sensitive and strictly quantitative data were obtained by inductively-coupled plasma mass spectrometry when using a triple quadrupole instrument (ICP-QqQ-MS). Our experiments provide data on the absolute cellular metal content of E. coli, an enrichment culture of "Ca. Kuenenia stuttgartiensis", Dehalococcoides mccartyi, Desulfovibrio vulgaris, Geobacter sulfurreducens and Geobacter metallireducens. A major obstacle in whole-cell metallomics is the interference caused by metal precipitates, observed for G. metallireducens and D. vulgaris. In the other investigated organisms, whole-cell metallomics gave biologically meaningful information, e.g. high Fe and Co content in "Ca. K. stuttgartiensis" and higher Mo content in E. coli when grown under nitrate-reducing conditions. The content of all four metals was almost constant in E. coli from the late exponential phase allowing precise measurements independent of the exact duration of cultivation. Deletion or overexpression of genes involved in metal homeostasis (Ni transport or Mo-cofactor metabolism) was mirrored by dramatic changes in whole-cell metal content. Deletion of genes encoding abundant metalloproteins or heterologous overexpression of metalloproteins was also reflected in the whole-cell metal content. Our study provides a reference point for absolute microbial metallomics and paves the way for the development of fast and easy mutation screens.

Heavy metals in coastal sediments of South Caspian Sea: natural or anthropogenic source?

This paper focuses on heavy metal distribution patterns in sediments of central Guilan (CG) and east Mazandaran (EM) in the south Caspian Sea coasts, north of Iran. Sediment sub-samples were retrieved from core and surficial samples in different environments of marine and coastal lagoons as well as coastal outcrops. Inductively Coupled Plasma Mass Spectrometry and Atomic Emission Spectrometry (ICP-MS and ICP-AES) analysis were used to determine the metal chemistry. Concentration of the selected heavy metals exhibited variations through sediment samples which are partially related to grain size and organic matter content. Geoaccumulation index and statistical procedures have been implemented for analyzing the absolute metal values. Result of the geoaccumulation index demonstrated that the metal distribution reflects the influence of geological background of the watershed area. Some elements including Pb, Ni, Cu, Sr and Ba showed elevated concentration in the CG that could be attributed to development of industrial activities. A comparison of the metal concentration in the marine sediments and the Late Holocene outcrops revealed that the level of the metals concentration at the sea generally corresponds to natural background. The northern part of Iranian multi-lithological catchments basin is the main source for the sediments that drained by the rivers to the South Caspian Sea basin

Identifying heavy metal levels in historical flood water deposits using sediment cores

When designing mitigation and restoration strategies for aquatic systems affected by heavy metal contamination, we must first understand the sources of these pollutants. In this study, we introduce a methodology that identifies the heavy metal levels in floodplain lake sediments deposited by one source; fluvial floods. This is done by comparing sediment core heavy metal profiles (i.e., historical pollution trends) to physical and chemical properties of sediments in these cores (i.e., historical flooding trends). This methodology is applied to Willsmere and Bolin Billabongs, two urban floodplain lakes (billabongs) of the Yarra River (South-East Australia). Both billabongs are periodically inundated by flooding of the Yarra River and one billabong (Willsmere Billabong) is connected to an urban stormwater drainage network. 1–2-m long sediment cores (containing sediment deposits up to 500 years old) were taken from the billabongs and analysed for heavy metal concentrations (arsenic, chromium, copper, lead, nickel, zinc). In cores from both billabongs, arsenic concentrations are high in the flood-borne sediments. In Bolin Billabong, absolute metal levels are similar in flood and non-flood deposits. In Willsmere Billabong, absolute copper, lead and zinc levels were generally lower in fluvial flood-borne sediments in the core compared to non-fluvial sediments. This suggests that heavy metal concentrations in Bolin Billabong sediments are relatively similar regardless of whether or not fluvial flooding is occurring. However for Willsmere Billabong, heavy metal concentrations are high when overland runoff, direct urban stormwater discharges or atmospheric deposition is occurring. As such, reducing the heavy metal concentrations in these transport pathways will be of great importance when trying to reduce heavy metal concentrations in Willsmere Billabong sediments. This study presents a proof-of-concept that can be applied to other polluted aquatic systems, to understand the importance of river floods in the contamination of the bed sediments of aquatic systems. As a cost effective and less time consuming alternative to extensive field monitoring, our proposed method can be used to identify the key sources of pollution and therefore support the development of effective management strategies.

Growth and photosynthetic responses of Lemna minor L. exposed to cadmium in combination with zinc or copper.

Metals have a variety of negative outcomes on plants, essential components of any ecosystem. The effects of CdCl2 (5 μmol L-1), ZnCl2 (25 or 50 μmol L-1), and CuCl2 (2.5 or 5 μmol L-1) and combinations of CdCl2 with either ZnCl2 or CuCl2 on the growth, photosynthetic pigments, and photosystem II (PSII) efficiency of duckweed (Lemna minor L.) were investigated. All of the treatments caused growth inhibition and remarkable metal accumulation in plant tissue after 4 and 7 days. In the combined treatments, the accumulation of each metal applied was lesser in comparison to treatments with single metals. After 4 days, all of the treatments generally diminished chlorophyll a content and decreased the maximum quantum yield (Fv/Fm) and effective quantum yield (ΔF/F'm) of PSII. However, after 7 days of exposure to a combination of Cd and Zn, pigment content and PSII activity recovered to control levels. A higher concentration of Cu (5 μmol L-1) as well as Cd in combination with Cu had a prolonged inhibitory effect on photosynthetic features. Our results suggest that growth inhibition was due to the toxic effect of absolute metal quantity in plant tissue. Zn counteracted Cd uptake, as seen from the recovery of pigment content and PSII efficiency in plants exposed for 7 days to the Cd and Zn combination. Cu-induced oxidative stress led to a prolonged inhibitory effect in plants treated both with a higher concentration of Cu (5 μmol L-1) and simultaneously with Cd and Cu. Our findings could contribute to general knowledge on anthropogenic and environmental contaminants that endanger plant communities and significantly disrupt the sensitive balance of an ecosystem by influencing photosynthetic mechanisms.

THE APOKASC CATALOG: AN ASTEROSEISMIC AND SPECTROSCOPIC JOINT SURVEY OF TARGETS IN THE KEPLER FIELDS

We present the first APOKASC catalog of spectroscopic and asteroseismic properties of 1916 red giants observed in the Kepler fields. The spectroscopic parameters provided from the Apache Point Observatory Galactic Evolution Experiment project are complemented with asteroseismic surface gravities, masses, radii, and mean densities determined by members of the Kepler Asteroseismology Science Consortium. We assess both random and systematic sources of error and include a discussion of sample selection for giants in the Kepler fields. Total uncertainties in the main catalog properties are of order 80 K in Teff , 0.06 dex in [M/H], 0.014 dex in log g, and 12% and 5% in mass and radius, respectively; these reflect a combination of systematic and random errors. Asteroseismic surface gravities are substantially more precise and accurate than spectroscopic ones, and we find good agreement between their mean values and the calibrated spectroscopic surface gravities. There are, however, systematic underlying trends with Teff and log g. Our effective temperature scale is between 0-200 K cooler than that expected from the Infrared Flux Method, depending on the adopted extinction map, which provides evidence for a lower value on average than that inferred for the Kepler Input Catalog (KIC). We find a reasonable correspondence between the photometric KIC and spectroscopic APOKASC metallicity scales, with increased dispersion in KIC metallicities as the absolute metal abundance decreases, and offsets in Teff and log g consistent with those derived in the literature. We present mean fitting relations between APOKASC and KIC observables and discuss future prospects, strengths, and limitations of the catalog data.

Inter-laboratory validation of bioaccessibility testing for metals

Bioelution assays are fast, simple alternatives to in vivo testing. In this study, the intra- and inter-laboratory variability in bioaccessibility data generated by bioelution tests were evaluated in synthetic fluids relevant to oral, inhalation, and dermal exposure. Using one defined protocol, five laboratories measured metal release from cobalt oxide, cobalt powder, copper concentrate, Inconel alloy, leaded brass alloy, and nickel sulfate hexahydrate. Standard deviations of repeatability (sr) and reproducibility (sR) were used to evaluate the intra- and inter-laboratory variability, respectively. Examination of the sR:sr ratios demonstrated that, while gastric and lysosomal fluids had reasonably good reproducibility, other fluids did not show as good concordance between laboratories. Relative standard deviation (RSD) analysis showed more favorable reproducibility outcomes for some data sets; overall results varied more between- than within-laboratories. RSD analysis of sr showed good within-laboratory variability for all conditions except some metals in interstitial fluid. In general, these findings indicate that absolute bioaccessibility results in some biological fluids may vary between different laboratories. However, for most applications, measures of relative bioaccessibility are needed, diminishing the requirement for high inter-laboratory reproducibility in absolute metal releases. The inter-laboratory exercise suggests that the degrees of freedom within the protocol need to be addressed.

Aluminium, iron and copper in human brain tissues donated to the medical research council's cognitive function and ageing study

Aluminium, iron and copper are all implicated in the aetiology of neurodegenerative diseases including Alzheimer's disease. However, there are very few large cohort studies of the content of these metals in aged human brains. We have used microwave digestion and TH GFAAS to measure aluminium, iron and copper in the temporal, frontal, occipital and parietal lobes of 60 brains donated to the Cognitive Function and Ageing Study. Every precaution was taken to reduce contamination of samples and acid digests to a minimum. Actual contamination was estimated by preparing a large number of (170+) method blanks which were interspersed within the full set of 700+ tissue digests. Subtraction of method blank values (MBV) from tissue digest values resulted in metal contents in all tissues in the range, MBV to 33 μg g(-1) dry wt. for aluminium, 112 to 8305 μg g(-1) dry wt. for iron and MBV to 384 μg g(-1) dry wt. for copper. While the median aluminium content for all tissues was 1.02 μg g(-1) dry wt. it was informative that 41 brains out of 60 included at least one tissue with an aluminium content which could be considered as potentially pathological (> 3.50 μg g(-1) dry wt.). The median content for iron was 286.16 μg g(-1) dry wt. and overall tissue iron contents were generally high which possibly reflected increased brain iron in ageing and in neurodegenerative disease. The median content for copper was 17.41 μg g(-1) dry wt. and overall tissue copper contents were lower than expected for aged brains but they were commensurate with aged brains showing signs of neurodegenerative disease. In this study we have shown, in particular, the value of carrying out significant numbers of method blanks to identify unknown sources of contamination. When these values are subtracted from tissue digest values the absolute metal contents could be considered as conservative and yet they may still reflect aspects of ageing and neurodegenerative disease in individual brains.

Effect Comparative and Experimental Analysis of Diffraction Sound Field Caused by Impedance Sphere and Elastic Spherical Shell on Directivity of Vector Sensor

The directivity of acoustic vector sensor (AVS) will be distorted by the sound diffraction of the AVS carrier. A common AVS carrier in accordance with its acoustic characteristics can be approximately classified into three types: absolute soft air cavity, absolute rigid solid metal body and elastic shell filled with air. The focus of this paper is placed on the pressure and vibration velocity component of diffraction acoustic field caused by impedance boundary and elastic spherical boundary. Their mathematical expressions are deduced, and their directivity is also analyzed at different frequencies for different impedances. The results show that: for impedance boundary, its influences on directivity of pressure and vibration velocity is decided by the diffraction background term, and for the elastic shell boundary filled with air, the diffraction acoustic field can be seen as the sum of the diffraction acoustic field of rigid boundary and the radiated sound field of elastic vibration spherical shell boundary. When the frequency of the incident plane wave deviates from the resonance frequency of the elastic vibration shell, the diffraction acoustic field of the rigid boundary plays a major role, but when the frequency of the incident plane wave is close to the resonance frequency, the radiated sound field of the elastic vibration shell will hold the dominance. The experimental data are treated and the errors between the experimental results and the theoretical results are analyzed.

Molecular structure and character of bonding of mono and divalent metal cations (Li+, Na+, K+, Mg2+, Ca2+, Zn2+, and Cu+) with guanosine: AIM and NBO analysis

The B3LYP/6-311++G (d,p) density functional approach was used to study the gas-phase metal affinities of Guanosine (ribonucleoside) for the Li+, Na+, K+, Mg2+, Ca2+, Zn2+, and Cu+ cations. In this study we determine coordination geometries, binding strength, absolute metal ion affinities, and free energies for the most stable products. We have also compared the results for Guanosine, with our previously reported results for 2′-Deoxyguanosine. Based on the results, it is obvious that MIA is strongly dependent on the charge-to-size ratio of the cation. Guanosine interacts more strongly with Zn2+ than do with Mg2+, Ca2+, and Cu+ and therefore stronger interactions lead to higher MIA. In both free molecules and their complexes, the Syn orientation of the base is stabilized by an intramolecular O5′–H···N3 hydrogen bond and the anti orientation of the base is stabilized by an intramolecular C–H···O hydrogen bond formed between the (C8-H8) and the O5′ atom of the sugar moiety. It is also interesting to mention that linear correlation between calculated MIA values and the atomic numbers (Z) of the metal ions of Li+, Na+, and K+ were found. Furthermore, the influences of metal cationization on the strength of the N-glycosidic bond, torsion angles, angle of pseudorotation (P), and intramolecular C–H···O and O–H···O hydrogen bonds have been studied. Natural bond orbital (NBO) analysis was performed to calculate the charge transfer and natural population analysis of the complexes. Quantum theory of atoms in molecules (QTAIM) was also applied to determine the nature of interactions.

On the binding of Mg2+, Ca2+, Zn2+ and Cu+ metal cations to 2 ′ -deoxyguanosine: Changes on sugar puckering and strength of the [formula omitted]-glycosidic bond

The binding of Mg2+, Ca2+, Zn2+ and Cu+ metal cations to 2′-deoxyguanosine has been analyzed, using the hybrid B3LYP, Density Functional Theory (DFT) method and 6–311++G(d,p) orbital basis sets. Coordination geometries, absolute metal ion affinities, and free energies for the most stable complexes formed by Mg2+, Ca2+, Zn2+ and Cu+ with the nucleoside, 2′-deoxyguanosine, have been determined. Furthermore, the influences of metal cationization on the strength of the N-glycosidic bond, torsion angles and angle of Pseudorotation (P) have been studied. With respect to the results, it has been found that metal binding significantly changes the values of the phase angle of Pseudorotation (P) in the sugar unit of these nucleosides. In all modified forms, the length of the C1′–N9 bond increases. The Mulliken population analysis on atomic charges has been carried out on the optimized geometries. Natural Bond Orbital (NBO) analysis was also performed to calculate the charge transfer and natural population analysis of the complexes. Quantum Theory of Atoms In Molecules (QTAIM) was also applied to determine the nature of interactions.

Application of Factor Analysis in Geochemical Speciation of Heavy Metals in the Sediments of a Lake System—Chilika (India): A Case Study

Abstract The geochemical association of some trace metals (Fe, Mn, Ni, Cu, Cr, and Pb) were sequentially extracted from bulk sediments of the Chilika lagoon, India. The low elemental concentration, except Pb, in the exchangeable phase suggests poor availability to bottom dwellers. However, slightly higher abundance of Pb in the exchangeable phase at station 4 (9.9%) and station 6 (9.5%) is mainly related with waste from major fishing jetties. The carbonate-bound phase reflects heavy metal distribution of detrital origin along with biological decomposition in the lagoon. A relatively higher percentage of Mn in the reducible phase is attributed to the flocculation of its colloids. The concentrations of Cu, Ni, and Pb show their higher affinity to the organic-bound fraction. The absolute metal concentrations in the residual fraction was Fe > Mn > Ni > Cu > Pb > Cr, which reflects the predominance of physical weathering, a high erosion rate, and a high sedimentation rate in the lagoon. According to Risk Asses...

Hybrid liquid metal–water cooling system for heat dissipation of high power density microdevices

The recent decades have witnessed a remarkable advancement of very large scale integrated circuits (VLSI) and electronic equipments in micro-electronic industry. Meanwhile, the ever increasing power density of microdevices leads to the tough issue that thermal management becomes rather hard to solve. Conventional water cooling is widely used, but the convective coefficient is not high enough. Liquid metal owns much higher convective coefficient and has been identified as an effective coolant recently, but the high cost greatly precludes its large scale utilization. In this paper, a hybrid liquid metal–water cooling system which combines the advantages of both water and liquid metal cooling was proposed and demonstrated. By utilizing a liquid metal “heat spreader” in front of the water cooling module, this system not only owns more excellent cooling capability than that based on water alone, but also has much lower initial cost compared with absolute liquid metal cooling system. A series of experiments under different operation conditions have been performed to evaluate the cooling performance of this hybrid system. The compared results with absolute water cooling and liquid metal cooling system showed that the cooling capability of the new system is competitive with absolute liquid metal cooling, but the initial cost could be much lower. The theoretical thermal resistance model and economic feasibility also have been analyzed and discussed, which shows that the hybrid liquid metal–water cooling system is quite feasible and useful.

DFT STUDY ON METAL CATIONIZATION AND O6-PROTONATION ON 2′-DEOXYGUANOSINE CONFIGURATION: CHANGES ON SUGAR PUCKERING AND STRENGTH OF THE N-GLYCOSIDIC BOND

Density functional theory (DFT) calculations were performed at the B3LYP/6-311++G (d, p) level to determine coordination geometries, absolute metal ion affinities, and free energies for all possible complexation stable products formed by monovalent metal cations including Li+ , Na+ , K+ with the nucleoside 2′-Deoxyguanosine. All computations indicate that the metal ion affinity (MIA) decreases on going from Li+ to Na+ and K+ for 2′-Deoxyguanosine. For example, the affinities for the metal ions described above are 75.2, 57.3, 43.4 kcal/mol, respectively. Furthermore, the influence of metal cationization and O6 protonation on the strength of the N-glycosidic bond, torsion angles and angle of pseudorotation (P) have been studied. With respect to the results, it has been found that metal binding significantly change the values of the phase angle of pseudorotation (P) in the sugar unit of these nucleosides but, O6 -protonation do not significantly change the values of the torsion angles and angle of pseudorotation (P). In all modified forms, the length of the C1'–N9 bond increases. The Mulliken population analysis and natural bond orbital (NBO) analysis on atomic charges have been carried out on the optimized geometries.

Interaction of Mg 2+, Ca 2+, Zn 2+ and Cu + with cytosine nucleosides: Influence of metal on sugar puckering and stability of N-Glycosidic bond, a DFT study

The coordination geometries, electronic features, absolute metal ion affinities, geometrical multiplicity and binding strength for the complexes formed by Mg 2+, Ca 2+, Zn 2+ and Cu + with cytidine and deoxycytidine have been determined theoretically employing the hybrid B3LYP exchange-correlation functional and using 6-311++G(d,p) orbital basis sets. Our study shows that the most stable coordination modes of cytosine nucleosides with these cations are rather similar. In the isolated state, the most stable form corresponds to a tridentate complex in which the cation interacts with three oxygen atoms: one from the carbonyl oxygen of cytosine moiety and two from the sugar unit (i.e., O5′ and O4′). The influences of metal cationization on the strength of the N-glycosidic bond, the values of the phase angle of pseudorotation P in the sugar unit and sugar ring conformation have been studied. In all cases, the N1 C1′ bond distance changes upon introducing positive charge in the nucleosides.