Order Ka Research Articles

Radiation Power of a Short High-Current Vacuum Arc at High Current Densities

The radiation of a vacuum arc was measured in the spectral region <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$200~\text {nm} \le \lambda \le 1100$ </tex-math></inline-formula> nm. The arc was initiated in the center of the cathode by breaking the current in the auxiliary circuit and was fed by the rectangular current pulse with a duration of 10 ms. The interelectrode gap was fixed at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$h = 4$ </tex-math></inline-formula> mm, and the butt <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2r =30$ </tex-math></inline-formula> -mm CuCr30 electrodes were used. The arc was stabilized by an external uniform axial magnetic field (AMF). The radiation was coming out of the vacuum chamber through quartz ultraviolet (KU)-1 quartz window. The radiation detector was a silicon photodiode with a diameter of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$d =1.2$ </tex-math></inline-formula> mm. It was located on an axis intersecting the axis of symmetry of the discharge in the center of the interelectrode gap. The distance from the diode to the axis of symmetry was <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L =1340$ </tex-math></inline-formula> mm. After amplification, the signal from the diode was recorded on an oscilloscope. The measurements were made in a range of currents from 10 to 25 kA in order to cover the modes with the anodic activity. It was found that under the conditions of these experiments, the anode activity begins to manifest itself at the end of the pulse, starting with currents exceeding 15 kA. As the current increases, the activity begins closer to the beginning of the pulse. Considering the type of the spectral sensitivity of the diode, two series of measurements were made—measurements without a filter and through a yellow filter ZhS-10 that cuts off radiation with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda \le400$ </tex-math></inline-formula> nm. The results obtained made it possible to analyze the dependence of the radiation power on the arc current. The results showed that at high current densities in the developed vacuum arc with anodic activity, a significant part of the power is transferred by radiation. At the end of a pulse with a current of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\approx 25$ </tex-math></inline-formula> kA, the radiation power is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\mathrm {uv}}~\approx ~150$ </tex-math></inline-formula> kW, while in the discharge, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{a} ~\approx ~800$ </tex-math></inline-formula> kW is released. That is, at high current densities at the end of the pulse, the radiation power reaches almost 20% of the power released in the arc at this time. Estimates of lateral losses due to radiation are made.

Variety and Distribution of Diatom-Based Sea Ice Proxies in Antarctic Marine Sediments of the Past 2000 Years

Antarctic sea ice is an essential component of the global climate system. Reconstructions of Antarctic sea ice from marine sediment cores are a vital resource to improve the representation of Antarctic sea ice in climate models and to better understand natural variability in sea ice over centennial and sub-centennial timescales. The Thomas et al. (2019) review of Antarctic sea ice reconstructions from ice and marine cores highlighted the prominence of diatom-based proxies in this research. Here, focusing solely on the diatom-based proxy records in marine sediments, we review the composition of proxies, their advantages and limitations, as well as the spatial and temporal cover of the records over the past 2 ka in order to assess the scope for future assimilation and standardization. The archive comprises 112 records from 68 marine cores, with proxies based on more than 30 different combinations of diatom taxa as well as the relatively new, highly branched isoprenoid (HBI) biomarkers.

Paleohydrological dynamics in the Western Mediterranean during the last glacial cycle

The transitional regions between the low and high latitudes of the Northern Hemisphere are highly vulnerable to future climate change yet most of the current climate models usually diverge in their projections. To better understand the dynamics in these regions, the reconstruction of past hydrological fluctuations and precipitation patterns is of paramount importance to accurately constrain present and future climate scenarios. In this study, we investigated paleohydrological dynamics in the western Mediterranean region, a transitional zone between low-mid latitudes and Atlantic - Mediterranean realms. We reconstruct precipitation and moisture source changes during the last ~35 ka in order to propose the potential mechanisms driving these oscillations. To do so, we use hydrogen isotopes from sedimentary leaf waxes, more specifically the C31 n-alkane homologue, and a precipitation proxy based on previously published pollen data from a sedimentary core (Padul-15-05) in southern Iberia (Padul wetland ~37° N). With this combination we disentangle the coupled effect of precipitation amount and source on the hydrogen isotopic signature of the studied C31 n-alkane record. Our results show three main periods characterized by different precipitation patterns. Low precipitation, mainly linked to a significant contribution from an isotopically-enriched Mediterranean precipitation source, occurred from ~30 to ~15.5 ka BP and during the last ~5 ka, whereas enhanced precipitation with a predominant isotopically-depleted Atlantic precipitation source prevailed from ~15.5 to ~5 ka BP. This latter stage is here defined as the Western Mediterranean Humid Period (WMHP). In addition, some occasional millennial-scale opposite precipitation patterns can be observed during these climatically distinct periods. These changes in the source of precipitation were likely coupled to a shift in the main rainy season from winter, when Atlantic precipitation prevailed, to late winter-early spring, when the contribution of Mediterranean moisture is higher. Comparison between the studied mid-latitude terrestrial Padul-15-05 core and a low-latitude marine record offshore of northwestern Africa shows clear long-term synchronous responses of both western Mediterranean precipitation and western African monsoon systems to northern Hemisphere atmospheric dynamics, ultimately controlled by orbital forcing and ice-sheets fluctuations.

Thermal Hydraulic Behavior of the First ITER CS Module

The ITER Central Solenoid (CS) modules are under fabrication by the US ITER organization and its subcontractors. US ITER will supply seven modules to the ITER Organization (IO), six of which will be assembled in a stack that forms the ITER Central Solenoid, the last one being spare. The first module, namely CSM 1 was manufactured by General Atomics (GA) and went through Factory Acceptance Tests (FAT) including high voltage testing, Paschen testing and then cold test at 4.5 K and up to 40.0 kA in order to demonstrate compliance with coil performance requirements. The paper focuses on the results of the first CS Module thermal hydraulic characterization without current (and field). Pressure drops, transit time, and thermal coupling between pancakes are presented. Analysis results and tests are also compared.

First ITER CS module test results

The ITER Central Solenoid (CS) is under fabrication by the US ITER organization and its subcontractors. US ITER will supply seven modules to ITER IO, six of which will be assembled in a stack that forms the ITER Central Solenoid, with one as a spare. The first module fabrication has been completed by General Atomics (GA) at their facility and has begun testing including high voltage testing, Paschen testing in the vacuum and then testing at 4.5 K and up to 40 kA in order to demonstrate compliance of the coil to ITER requirements. In the paper we present the Test Plan and results of the CS Module performance tests, especially at 40 kA current. AC losses, joint resistances and hydraulic characteristics of the coil are all measured. Displacements of the coil height and hoop strain of the CS Module are also measured to verify structural and mechanical characteristics of the coil along with cooldown shrinkage of the coil. This information is used for verification of the stack behavior of CS in ITER operation. The test results and preliminary analyses results are presented, compared to expectations, and discussed. All measured parameters suggest that the CS module will perform well in ITER machine.

Quadruplex-Duplex Junction: A High-Affinity Binding Site for Indoloquinoline Ligands.

A parallel quadruplex derived from the Myc promoter sequence was extended by a stem‐loop duplex at either its 5′‐ or 3′‐terminus to mimic a quadruplex–duplex (Q–D) junction as a potential genomic target. High‐resolution structures of the hybrids demonstrate continuous stacking of the duplex on the quadruplex core without significant perturbations. An indoloquinoline ligand carrying an aminoalkyl side chain was shown to bind the Q–D hybrids with a very high affinity in the order K a≈107 m −1 irrespective of the duplex location at the quadruplex 3′‐ or 5′‐end. NMR chemical shift perturbations identified the tetrad face of the Q–D junction as specific binding site for the ligand. However, calorimetric analyses revealed significant differences in the thermodynamic profiles upon binding to hybrids with either a duplex extension at the quadruplex 3′‐ or 5′‐terminus. A large enthalpic gain and considerable hydrophobic effects are accompanied by the binding of one ligand to the 3′‐Q–D junction, whereas non‐hydrophobic entropic contributions favor binding with formation of a 2:1 ligand‐quadruplex complex in case of the 5′‐Q–D hybrid.

Controlling Foam Stability with the Ratio of Myristic Acid to Choline Hydroxide.

The interfacial and foam properties of a model system based on the mixture between myristic acid and choline hydroxide have been investigated as a function of the molar ratio ( R) between these two components and temperature. The aim of this study was to obtain insight on the links between the self-assemblies in bulk and in the foam liquid channels, the surfactant packing at the interface, and the resulting foam properties and stability. A multiscale approach was used combining small angle neutron scattering, specular neutron reflectivity, surface tension measurements, and photography. We highlighted three regimes of foam stability in this system by modifying R: high foam stability for R < 1, intermediate at R ∼ 1, and low for R > 1. The different regimes come from the pH variations in bulk linked to R. The pH plays a crucial role at the molecular scale by setting the ionization state of the myristic acid molecules adsorbed at the gas-liquid interface, which in turn controls both the properties of the monolayer and the stability of the films separating the bubbles. The main requirement to obtain stable foams is to set the pH close to the p Ka in order to have a mixture of protonated and ionized molecules giving rise to intermolecular hydrogen bonds. As a result, a dense monolayer is formed at the interface with a low surface tension. R also modifies the structure of self-assembly in bulk and therefore within the foam, but such a morphological change has only a minor effect on the foam stability. This study confirms that foam stability in surfactant systems having a carboxylic acid as polar headgroup is mainly linked to the ionization state of the molecules at the interface.

An electrically small antenna for nearfield biomedical applications

AbstractThe size of electrically small antennas is quite lesser than wavelength, typically in range of λ/10 or lesser. These antennas offer vital application in space constraint environment such as small biomedical equipment or passive radio frequency identification applications. The antenna having size of 20 mm × 15 mm (0.16λ × 0.125λ) is proposed. Slots on the patch are engineered for target resonance and bandwidth enhancement. The antenna offers bandwidth in order of 7.6% and product ka in order of 0.62. The prototype is fabricated and measured results are presented, which are well suited for ISM band applications.

EFFECT OF ACID–BASE PROPERTY OF INORGANIC NANOPARTICLES ON ANTIFOULING PERFORMANCE OF PVDF COMPOSITE ULTRAFILTRATION MEMBRANES

Pure poly(vinylidene fluoride) (PVDF) membrane and PVDF composite membranes modified by three kinds of inorganic nanoparticles ( SiO 2, Al 2 O 3, and TiO 2) were made using a phase inversion method and characterized by pure water flux, retention efficiency of Bovine serum albumin (BSA), flux reduction coefficient, and scanning electron microscope (SEM). The results of flux reduction coefficient illustrated that PVDF membrane modified by nanoparticles had better antifouling property in the order of TiO 2, Al 2 O 3, SiO 2. The Lewis acid–base properties of the nanoparticle materials were measured by inverse gas chromatography (IGC). The Lewis acid number, Ka, and Lewis base number, Kb, had the following order Ka TiO 2 &lt; Ka Al 2 O 3 &lt; Ka SiO 2, and Kb TiO 2 &gt; Kb Al 2 O 3 &gt; Kb SiO 2. The experimental results indicated that PVDF membrane modified by nanoparticles with relatively strong base exhibited excellent antifouling performance.

Of Folding and Function: Understanding Active-Site Context through Metalloenzyme Design

In the emerging field of biomolecular design, the introduction of metal-binding sites into loop or turn regions of known protein scaffolds has been utilized to create unique metalloprotein and metallopeptide systems for study. This Forum Article highlights examples of the modular-turn-substitution approach to design and the range of structural and mechanistic questions to which this tool can be applied. Examples from the authors' laboratory are given to show that lanthanide-binding metallopeptides, and now a full metallohomeodomain, can be generated by modular substitution of a Ca-binding EF-hand loop into the unrelated scaffold, the engrailed helix-turn-helix motif. We have previously shown that these peptides bind trivalent Ln(III) ions and promote DNA and phosphate hydrolysis, the targeted function. Here, a series of chimeric peptides are presented that differ only in the ninth loop position [given in parentheses; Peptides P3N (Asn), P3E (Glu), P3A (Ala), and P3W(D) (Asp]. This residue, a putative second-shell ligand stabilizing a coordinated water, was found to influence not only metal affinity but also peptide folding. The affinity for Tb(III) was determined by Trp-Tb fluorescence resonance energy transfer and followed the order Ka = P3W(D) > P3A approximately P3E > P3N. However, circular dichroism (CD) titrations with EuCl3 showed that only P3W(D) and P3N folded to any extent upon metal binding, indicating that the Asp/Asn side chains stabilize the central loop structure and thus propagate folding of the peripheral helices, whereas neither Ala nor Glu appears to be interacting with the metal to organize the loop. Finally, we investigated the longer range context of a given loop substitution by cloning and expressing a lanthanide-binding homeodomain (C2), whose loop insertion sequence is analogous to that of peptide P3W(D). We find by CD that apo-C2 has a significant helical structure (approximately 25% alphahelicity), which increases further upon the addition of Tb(III) (approximately 32% alpha helicity). The protein's Tb(III) affinity is similar to that of the chimeric peptides. However, unlike previously reported metallopeptides, we find that EuC2 does not appreciably promote phosphate or DNA cleavage, which suggests a difference in metal accessibility in the context of the full domain. We have demonstrated that substituting beta turns with metal-binding turns does not necessarily require homologous parental scaffolds or small flexible peptides but rather relies on the structural similarity of the motifs flanking the turn.

IMPLICATIONS OF PLANKTIC FORAMINIFERAL SIZE FRACTIONS FOR THE GLACIAL-INTERGLACIAL PALEOCEANOGRAPHY OF THE POLAR NORTH ATLANTIC

Foraminiferal abundances derived from different mesh-size fractions were investigated from the polar North Atlantic for the time interval of the later part of marine oxygen isotope (MIS) 8 into early MIS 7 and the last 30 cal. ka in order to select the most representative fraction for paleoceanographic applications. The records cover the time interval with quite different glacial-interglacial climatic conditions. Whereas the interval of MIS 8–7 represents “intermediate” glacial-interglacial conditions, the younger core section characterizes more extreme climatic conditions consisting of the rather cold last glacial maximum (LGM) and the very warmer Holocene. The records from MIS 8 to 7 show that the larger size fractions (125–250 μm, >150 μm) reveal almost monospecific assemblages of the polar species Neogloboquadrina pachyderma (s), indicating a prevalence of cold polar-like surface water conditions during this time. By contrast, the smaller size fractions (100–150 μm, 80–150 μm) exhibit considerable increase of the subpolar species Turborotalita quinqueloba, which is representative of inflow of Atlantic water into the polar North Atlantic. In these smaller fractions, the two species show a strong negative correlation with respect to changes in glacial-interglacial conditions. Although T. quinqueloba yielded sufficiently high numbers of total specimens in the two smallest fractions, which makes this species useful for interpreting temporal water mass alterations, the relative abundance changes in the 80–150 μm are twice as large as in the 100–150 μm fraction. Size fraction faunal analysis covering the last 30 cal. ka revealed occurrences of small-sized T. quinqueloba (80–150 μm) in the LGM interval, indicating seasonally open water conditions during this time. This finding demonstrates the advantage of employing small-sized fractions for paleoceanographic reconstructions of periods when relatively cold conditions prevailed in the Nordic seas.

Clay mineral evidence of nepheloid layer contributions to the Heinrich layers in the northwest Atlantic

The clay fraction of four cores drilled in the north Atlantic Ocean was studied at a very high resolution over the last 150 ka in order to record the mineralogical signature of Heinrich events. Factor analysis of clay mineralogy establishes that three independent factors represent the main variations: a `detrital factor' (illite + chlorite + kaolinite), a `smectite factor', and a `mixed-layer factor' (IVML: illite-vermiculite mixed-layered clay). The clay mineral fraction of core SU90-38 drilled in the northeastern Atlantic basin did not record any Heinrich event, whereas large changes in the clay mineral fraction occurred during Heinrich events H1, H2, H4, and H5 in the three cores from the northwestern Atlantic basin (cores SU90-08, SU90-11, and SU90-12). Heinrich layers are characterized by increases in the detrital factor in cores SU90-08 and SU90-11, and sharp increases in the mixed-layer factor in cores SU90-11 and SU90-12. The geographical setting of the cores, the pattern of surface, intermediate and deep water circulation, and the main sources of clay minerals allow recognition of two major mechanisms involved in the deposition of the Heinrich Layers: (1) an increased supply of detrital clay minerals by the icebergs; and (2) a specific input of illite-vermiculite mixed-layer clay minerals by a nepheloid layer.

Comparison between self-field AC losses of a single-phase Bi-2223 cable measured by electric and calorimetric methods

High- T c power cables based on Bi-2223 tapes are under development worldwide. An important parameter for design and cost optimization is the AC loss expected during 50/60 Hz operation. Its measurement can be affected by several experimental problems that may alter the results. For this purpose, the 50 Hz losses of a 1.5 m long conductor, made by helically winding four layers of Bi-2223 tapes, were measured simultaneously by electrical and calorimetric methods in a wide range of currents up to 2 kA in order to investigate the reasons for possible discrepancies. The present, specifically designed, calorimetric system is not based on temperature distribution analysis but on the measurement of the gas boil-off rate of the liquid nitrogen bath.

Calculation of the Response of an Impulsively Excited Oscillator in an Infinite Acoustic Fluid

The response of an impulsively excited single-degree-of-freedom oscillator submerged in an infinite acoustic fluid is considered. The character of the response is determined by the quantity ka; k is the wave number associated with the in-vacuo natural frequency of the oscillator, and a is a characteristic structural dimension. For low-frequency oscillators (ka ≪ 1), the response consists of two parts. The first is the usual hydrodynamic solution in which the effect of the fluid on the structure is that of an added mass. The second is much smaller (of order ka) and is significant only in a “boundary layer” in time of order a/c, with c the fluid sonic velocity. For high-frequency oscillators (ka ≫ 1), the principal effect of the fluid is a decay of oscillator vibration due to sound radiation.

The Conductance of Sodium Perchlorate in Water-sulfolane Mixtures at 35 °C

Abstract Measurements on the conductance of dilute solutions of sodium Perchlorate, at 35 °C, in water-sulfolane mixtures over the entire solvent composition range are reported. Experimental data were analyzed by the 1965 Fuoss-Onsager-Skinner equations. No detectable ion association was found for this electrolyte, unlike sodium chloride in the same solvent mixtures. The association order KA(Cl-)&gt;KA(ClO4 -) is in contrast with that observed in protic solvents [KA(ClO4 -)&gt;KA(Cl-)] and is similar to that found in aprotic solvents. This shows that in water-sulfolane mixtures, association phenomena are mainly controlled by sulfolane. The lack of transport numbers for water-sulfolane mixtures precludes unambiguous explanations for Waiden products A0η.