Delta Forms Research Articles

Torsion in cohomology and dimensional reduction

Conventional wisdom dictates that ℤN factors in the integral cohomology group Hp(Xn, ℤ) of a compact manifold Xn cannot be computed via smooth p-forms. We revisit this lore in light of the dimensional reduction of string theory on Xn, endowed with a G-structure metric that leads to a supersymmetric EFT. If massive p-form eigenmodes of the Laplacian enter the EFT, then torsion cycles coupling to them will have a non-trivial smeared delta form, that is an EFT long-wavelength description of p-form currents of the (n − p)-cycles of Xn. We conjecture that, whenever torsion cycles are calibrated, their linking number can be computed via their smeared delta forms. From the EFT viewpoint, a torsion factor in cohomology corresponds to a ℤN gauge symmetry realised by a Stückelberg-like action, and calibrated torsion cycles to BPS objects that source the massive fields involved in it.

Monomeric and Dimeric Carboxylic Acid in Crystalline Cavities and Channels of Delta and Epsilon Forms of Syndiotactic Polystyrene.

Delta (δ) and epsilon (ε) co-crystalline forms of syndiotactic polystyrene with a carboxylic acid guest were obtained by sorption of liquid hexanoic acid in syndiotactic polystyrene films exhibiting delta and epsilon nanoporous-crystalline forms. The characterization study is facilitated by axially stretched syndiotactic polystyrene films, used both for polarized FTIR spectra and for WAXD fiber patterns. Particularly informative are two carbonyl-stretching FTIR peaks, attributed to monomeric and dimeric hexanoic acid. The dichroism of these carbonyl peaks indicates that both delta and epsilon phases are able to include hexanoic acid as isolated guest molecules, while only the epsilon phase is also able to include dimeric hexanoic acid molecules in its crystalline channels. The inclusion of both isolated and dimeric hexanoic acid species in the epsilon form crystalline channels produces extremely fast hexanoic acid uptakes by syndiotactic polystyrene epsilon form films.

Influence of the El Niño Phenomenon on Shoreline Evolution. Case Study: Callao Bay, Perú

Analyzing the long-term behavior of the coastlines in the vicinity of river mouths and estuaries usually relies on the mean (predicted) values of the sediment discharge from the river. However, this approach does not consider low frequency, severe events, such as El Niño (EN), that can have a large effect on coastlines. While the effects of an EN on flooding and droughts are well studied, little information exists about its effects on coastal zones, and especially on the evolution of coastlines. In early 2017, an EN occurred in the equatorial Pacific Ocean, and the country of Peru was affected with high precipitation levels, and extreme river discharges and flooding. During this event, in the district of Lima, the Rimac River discharged a huge amount of sediment into the Callao Bay, and the shoreline accreted approximately 1 km, demonstrating the significant effects that an EN can have on coastal zones. To explore these effects, this paper studies the influence of an EN on shoreline evolution in the Callao Bay by analyzing Landsat images from 1985–2019 to understand the shoreline evolution and identify changes to the coastline. Results show that when an extraordinary EN occurs (e.g., 1982–1983, 1997–1998, and 2017), the shoreline experiences high accretion compared to when a smaller, or no EN occurs. During these events, a significant delta forms at the south end of the bay, and the redistribution of the accumulated sediment by wave action causes the accretion of the adjacent coastlines for as far as 7 km north of the river mouth. This shows the importance of these events for the wellbeing of coastlines adjacent to river mouths affected by EN.

Conceptualizing delta forms and processes in Arctic coastal environments

AbstractClimate warming in the Arctic directly causes two opposite changes in Arctic coastal systems: increased melt‐water discharge through rivers induces extra influx of sediments and extended open water season increases wave impact which reworks and erodes the shores. A shoreline change analysis along the southern coast of Disko Island in western Greenland was conducted with aerial photographs and satellite images from 1964, 1985, and 2012. The decadal morphologic evolution of this 85 km section showed that large parts of the coast had undergone very limited changes. However, two deltas were highly dynamic and popped up as hotspots.The Tuapaat delta and Skansen delta showed large progradation rates (1.5 and 7 m/yr) and migration of the adjacent barriers and spits. The dynamic behavior at the delta mouths was mainly caused by classic delta channel lobe switching at one delta (Tuapaat), and by a breach of the fringing spit at the other delta (Skansen). The longshore and cross‐shore transports are responsible for reworking the sediment with a result of migrating delta mouths and adjacent subaqueous mouth bars. Seaward progradation of the deltas is limited due to the steep nature of the bathymetry in Disko Bay.Finally, a schematic conceptual overview of processes and associated morphological responses for deltas in Arctic environments is presented, including the climate drivers affecting delta evolution. Copyright © 2016 John Wiley & Sons, Ltd.

Abstract 190: Targeting ceramide and endoplasmic reticulum-stress in vitamin E induced apoptosis in human breast cancer cells

Abstract Vitamin E consists of eight plant-derived forms classified as tocopherols (α, β, Δ, γ) and tocotrienols (α, β, Δ, γ) which have a chromanol ring and a saturated and unsaturated aliphatic side chain, respectively. The anti-cancer actions of tocopherols and tocotrienols are limited to the gamma and delta forms. Here, we report that both γ-tocopherol (γT) and γ-tocotrienol (γT3) display potent anti-cancer actions with γT3 being more potent. Both forms target similar pro-apoptotic and anti-apoptotic pathways. γT and γT3 induced apoptosis in human breast cancer cells by enhancing death-receptor DR5 mediated activation of caspase-8 and mitochondria dependent caspase-9, as well as by activating ER-stress markers: GADD153/ C/EBP homologous protein (CHOP), GRP-78, ATF-4 and eIF2α. JNK and CHOP are involved in DR5 mediated apoptosis triggered by both vitamin E forms. γT and γT3 decreased protein levels of anti-apoptotic factors c-FLIP, BCl-2 and survivin. Since ceramide is a known upstream inducer of ER-stress and downstream mediator of death receptor apoptotic pathway mediators, treatments with γT and γT3 were conducted in the presence of specific inhibitors of sphingomyelin hydrolysis, de novo ceramide pathways and ER-stress in order to distinguish between the pathways modulated by the vitamin E forms. Data show that both γT and γT3 induced apoptosis via activation of sphingomyelin hydrolysis and the de novo ceramide pathways; however, activation of the ER-stress pathway contributed to apoptosis induced by γT3 only. Taken together, our data suggest that γT3s more potent apoptotic effects in comparison to γT are due to the ability of γT3 to activate ER stress pathways. This better understanding of the anti-cancer properties and mechanistic actions by these two natural occurring agents in vitro provides the necessary impetus to test them in combination with other known anti-cancer agents in pre-clinical xenograft studies to identify novel and safer therapeutic strategies. Research funded by The Clayton Foundation for Research. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 190. doi:10.1158/1538-7445.AM2011-190

Controlling Helical Chirality in Atrane Structures: Solvent‐Dependent Chirality Sense in Hemicryptophane‐Oxidovanadium(V) Complexes

The diastereomeric hemicryptophane oxidovanadium(V) complexes (P)-(S,S,S)-3 and (M)-(S,S,S)-4 have been synthesized. (1)H and (51)V NMR spectra in solution are consistent with the formation of Lambda and Delta forms of the propeller-like vanatrane moiety, leading to two diastereomeric conformers for each complex: that is, (P)-(S,S,S-Lambda)-3/(P)-(S,S,S-Delta)-3 and (M)-(S,S,S-Lambda)-4/(M)-(S,S,S-Delta)-4. The Lambda/Delta ratio is rather temperature-insensitive but strongly dependent on the solvent (the de of (M)-(S,S,S)-4 changes from 0 in benzene to 92 % in DMSO). The solvent therefore controls the preferential clockwise or anticlockwise orientation of the propeller-like atrane unit. The energy barriers for the Lambdaright arrow over left arrowDelta equilibrium were determined by NMR experiments, and the highest DeltaG( not equal) value (103.7 kJ mol(-1)) was obtained for (P)-(S,S,S)-3, much higher than those reported for other atrane derivatives. This is attributed to the constraints arising from the cage structure. Determination of the activation parameters provides evidence for a concerted, rather than a stepwise, interconversion mechanism with entropies (DeltaS( not equal)) of -243 and -272 J mol(-1) K(-1) for (P)-(S,S,S)-3 and (M)-(S,S,S)-4, respectively. The molecular structure of the (P)-(S,S,S-Lambda)-3 isomer was solved by X-ray diffraction and shows a distorted structure with one of the linkers located in the CTV cavity. Complementary quantum chemical calculations were carried out to obtain the energy-minimized structures of (P)-(S,S,S)-3 and (M)-(S,S,S)-4. Our density functional theory calculations suggest that the (P)-(S,S,S-Lambda)-3 is favored, in agreement with experimental data. For the M series, a similar strategy was used to extract molecular structures and relative energies. As in the case of the P diastereomer, the Lambda form dominates over the Delta one.

Dioxomolybdenum(VI) Complexes with Ene-1,2-dithiolate Ligands: Synthesis, Spectroscopy, and Oxygen Atom Transfer Reactivity

New dioxomolybdenum(VI) complexes, (Et(4)N)(Ph(4)P)[Mo(VI)O(2)(S(2)C(2)(CO(2)Me)(2))(bdt)] (2) and (Et(4)N)(Ph(4)P)[Mo(VI)O(2)(S(2)C(2)(CO(2)Me)(2))(bdtCl(2))](4)(S(2)C(2)(CO(2)Me)(2) = 1,2-dicarbomethoxyethylene-1,2-ditholate, bdt = 1,2-benzenedithiolate, bdtCl(2) = 3,6-dichloro-1,2-benzenedithiolate), that possess at least one ene-1,2-dithiolate ligand were synthesized by the reaction of their mono-oxo-molybdenum(IV) derivatives, (Et(4)N)(2)[Mo(IV)O(S(2)C(2)(CO(2)Me)(2))(bdt)] (1) and (Et(4)N)(2)[Mo(IV)O(S(2)C(2)(CO(2)Me)(2))(bdtCl(2))] (3), with Me(3)NO. Additionally, the bis(ene-1,2-dithiolate)Mo(VI)O(2) complex, (Et(4)N)(Ph(4)P)[Mo(VI)O(2)(S(2)C(2)(CO(2)Me)(2))(2)] (6), was isolated. Complexes 2, 4, and 6 were characterized by elemental analysis, negative-ion ESI mass spectrometry, and IR spectroscopy. X-ray analysis of 4 and 6 revealed a Mo(VI) center that adopts a distorted octahedral geometry. Variable-temperature (1)H NMR spectra of (CD(3))(2)CO solutions of the Mo(VI)O(2) complexes indicated that the Mo centers isomerize between Delta and Lambda forms. The electronic structures of 2, 4, and 6 have been investigated by electronic absorption and resonance Raman spectroscopy and bonding calculations. The results indicate very similar electronic structures for the complexes and considerable pi-delocalization between the Mo(VI)O(2) and ene-1,2-dithiolate units. The similar oxygen atom transfer kinetics for the complexes results from their similar electronic structures.

Delta progradation driven by an advancing sediment source: Coupled theory and experiment describing the evolution of elongated deltas

Most of the models of alluvial fan and delta morphodynamics to date have used one of two assumptions concerning the upstream boundary condition: (1) a fixed sediment feed point at the vertex or (2) a feed point corresponding to a bedrock‐alluvial transition that, e.g., migrates upstream under conditions of constant base level. Here, however, we present both experimental and numerical results pertaining to a new configuration, i.e., one in which the sediment feed point migrates downstream. The research is motivated by the operation of the tailings pond of a mine in which a delta forms. The mine operators must frequently move the outfalls of their slurry pipelines downstream to avoid their burial under sediment as the delta aggrades. This downstream migration results in a characteristic delta configuration. Under the right conditions, as the tailings delta progrades downstream, it does not have time to fill all the available space in the lateral direction, thus leaving unfilled open water on either side. The result is the formation of an elongated delta. Here we use both experiments and numerical modeling to characterize the control of the feed point migration rate on the lateral extent of the prograding deltas. We use these results to obtain a partial explanation of natural elongated deltas. In the case of such deltas, the downstream progradation of natural levees provides an analog to the downstream migration of the outfall of a slurry pipeline.

Study of integer quantum Hall effect in systems with isotropic and non-isotropic impurities

In this paper, we study the integer quantum Hall effect (IQHE) in systems with different types of impurities, considering the IQHE as a consequence of gauge invariance and the existence of a mobility gap. We consider the response of the Landau energy levels to a change of flux, in the presence of impurities in delta and Gaussian forms (in which the impurities are distributed isotropically). Then, we add a specified form of a quantum dot potential to the system with isotropic impurities, and observe the Hall effect and study the behavior of the system. Finally, we add non-isotropic impurities in systems showing the IQHE. We observe that if the impurity distribution is in the same direction in which the electric field is applied, the localized levels move out from the origin with respect to the isotropic case, and the Hall step will be clearly observed.

Enantiospecific synthesis of delta and lambda [Ru(bpy)(2)ppy](+) and [Ru(bpy)(2)quo](+) (bpy = 2,2'-bipyridine, ppy = phenylpyridine-H(+), quo = 8-hydroxyquinolate): (1)H and (13)C NMR studies and X-ray structure determination of rac-[Ru(bpy)(2)quo]PF(6).

In this paper, we describe the enantiospecific synthesis and the complete characterization of the two hexacoordinated ruthenium(II) monocations [Ru(bpy)(2)ppy](+) and [Ru(bpy)(2)quo](+) (bpy = 2,2'-bipyridine, ppy = phenylpyridine-H(+), quo = 8-hydroxyquinolate) in their enantiomeric Delta and Lambda forms. The corresponding enantiomeric excesses (ee's) are determined by (1)H NMR using pure Delta-Trisphat (tris(tetrachlorobenzenedialato)phosphate(V) anion) as a chiral (1)H NMR shift reagent. A complete (1)H and (13)C NMR study has been carried out on rac-[Ru(bpy)(2)ppy]PF(6) and rac-[Ru(bpy)(2)quo]PF(6). Additionally, the X-ray molecular structure of rac-[Ru(bpy)(2)quo]PF(6) is reported; this latter species crystallizes in the monoclinic C2/c space group (a = 22.079 A, b = 16.874 A, c = 17.533 A, alpha = 90 degrees, beta = 109.08 degrees, gamma = 90 degrees ).

Down-regulation of Delta by proteolytic processing.

Notch signaling regulates cell fate decisions during development through local cell interactions. Signaling is triggered by the interaction of the Notch receptor with its transmembrane ligands expressed on adjacent cells. Recent studies suggest that Delta is cleaved to release an extracellular fragment, DlEC, by a mechanism that involves the activity of the metalloprotease Kuzbanian; however, the functional significance of that cleavage remains controversial. Using independent functional assays in vitro and in vivo, we examined the biological activity of purified soluble Delta forms and conclude that Delta cleavage is an important down-regulating event in Notch signaling. The data support a model whereby Delta inactivation is essential for providing the critical ligand/receptor expression differential between neighboring cells in order to distinguish the signaling versus the receiving partner.

The role of hepatic peroxisome proliferator‐activated receptors (PPARs) in health and disease

The liver has long been known to respond to exposure to certain chemicals with hyperplasia and proliferation of the peroxisomal compartment. This response is now known to be mediated by specific receptors. The peroxisome proliferator-activated receptors (PPARs) were cloned 10 years ago, and in that interval, have been found to serve as receptors for a number of endogenous lipid compounds, in addition to the peroxisome proliferators that originally led to their study. Three receptors, designated the alpha, delta, and gamma receptors, have been found in mammals. PPARalpha: is the most abundant form found in the liver, with smaller amounts of the delta and gamma forms also expressed there. Kupffer cells, like other macrophages, appear to express the alpha and gamma isoforms. Hepatic stellate cells are reported to express the gamma isoform. PPARalpha knock-out mice fail to undergo peroxisome proliferation when challenged with the proliferators. Moreover, they have severe derangements of lipid metabolism, particularly during fasting, indicating that normal function of the alpha receptors is needed for lipid homeostasis. This in turn suggests that inadequate PPAR-mediated responses may contribute to abnormal fatty acid metabolism in alcoholic and non-alcoholic steatohepatitis. Recent information suggests that PPARgamma receptors may be important in control of the activation state of the stellate cells, and their repression or inactivation may predispose to hepatic fibrosis. The first approved drug that specifically activates PPARgamma, troglitazone, has rarely been found to cause serious liver injury. Although this is likely to represent an idiosyncratic reaction, the medical community will need to be alert to the possibility that activation or blockade of these receptors may cause hepatic dysfunction.

Oriented lake-and-ridge assemblages of the Arctic coastal plains: glacial landforms modified by thermokarst and solifluction

AbstractOriented assemblages of parallel ridges and elongated lakes are widespread on the coastal lowlands of northeast Eurasia and Arctic North America, in particular, in Alaska, Arctic Canada, and northeast Siberia. So far, only the oriented lakes have been of much scientific interest. They are believed to be formed by thermokarst in perennially frozen ice-rich sediments, while their orientation is accounted for either by impact of modern winds blowing at right angles to long axes of the lakes (when it concerns individual lakes), or by the influence of underlying bedrock structures (in the case of longitudinal and transverse alignment of lake clusters).En masseexamination of space images suggests that oriented lake-and-ridge assemblages, not the oriented lakes alone, occur in the Arctic. Hence any theory about their formation should account for the origin and orientation of the assemblages as a whole. The existing hypotheses appear inadequate for this end, so this paper proposes that the assemblages were initially created by glacial activity, that is, by ice sheets that drumlinized and tectonized their beds, as well as by sub- and proglacial meltwater, and then they were modified by thermokarst, solifluction, and aeolian processes. This assumption opens up an avenue by which all known features of oriented landforms in the Arctic can be explained. The paper suggests that the oriented landforms in Siberia and Alaska are largely signatures of a marine Arctic ice sheet that transgressed from the north, while the Baffin Island and Mackenzie Delta forms were created by the respective sectors of the Laurentide ice sheet. The oriented features discussed belong to the last Late Glacial through the Early Holocene.

Polymorphism of syndiotactic polystyrene. Morphology of the solvent-induced crystalline forms

Abstract The morphology of the delta and gamma forms of syndiotactic polystyrene (sPS) was investigated using scanning electron microscopy. The crystalline forms, delta and gamma, characterized by the chains in helical conformation, were obtained by solvent-induced crystallization from the amorphous glassy polymer. Dichloromethane and acetone were used to obtain the delta and the gamma form, respectively. The last form was obtained by thermal treatments of the delta form, too. The surface of the solvent-crystallized samples shows a texture characterized by oriented elements and cavities, whereas the internal part is microspherulitic in the case of the delta form and is more complex in the gamma form. At variance, the gamma form obtained by annealing the delta form shows a much more regular microspherulitic texture.

ARIA is concentrated in nerve terminals at neuromuscular junctions and at other synapses

Skeletal muscle ACh receptors (AChRs) accumulate at neuromuscular junctions (nmjs) at least partly because of the selective induction of AChR subunit genes in subsynaptic myotube nuclei by the motor nerve terminal. Additionally, mammalian AChRs undergo a postnatal change in subunit composition from embryonic (alpha 2 beta gamma delta) to adult (alpha 2 beta epsilon delta) forms, a switch that also depends on innervation. ARIA, a protein purified from chicken brains based on its ability to induce AChR synthesis in primary chick muscle cells, is a strong candidate for being the molecule responsible for these early developmental events. ARIA mRNA has been detected in embryonic motor neurons during synapse formation, and the gene continues to be expressed postnatally. In this report, we provide evidence that ARIA-like immunoreactivity is concentrated in rat motor nerve terminals from early postnatal ages, and that it can be detected in motor neurons in E18 embryos. ARIA is also detectable in axons within colchicine-treated sciatic nerves, suggesting that the protein in the nerve terminal has been transported from the cell body. ARIA mRNA is present in, but not restricted to, cholinergic neurons. Likewise, we report here that ARIA-like immunoreactivity is present in some noncholinergic central synapses. We also present evidence that isoforms of ARIA are differentially distributed among functionally distinct classes of neurons.

The detection of lupus anticoagulant using the kaolin clotting time test: A comparative study of the different forms of analysis

This work is a report of a comparative study between the different forms of analysis (curve, index, percentage and delta) of kaolin clotting time (KCT) for the detection of lupus anticoagulant. The reference values for all tests were defined from a study of 111 normal controls. 133 patients were studied, 106 with connective tissue disease and 27 with syphilis. LA was detected in 31 of the 133 patients studied. For KCT, the percentage and the delta showed greater sensitivity (61% and 65%, respectively) as opposed to the curve and the index (48% and 26%, respectively). We found significant statistical differences between the frequency of positivity of the index and the delta (p < 0.001) and between the index and the percentage (p < 0.005). Our findings show that if it is necessary to use KCT as a complementary test for the detection of LA, then it is more convenient to carry it out by using the percentage or the delta forms of analysis.

Computer modelling of the influence of tectonics on sequence architecture of coarse-grained fan deltas

Fan delta deposition and extensional faulting are combined in a computer model using a general tectonosedimentary forward modelling equation. Fan delta forms and architectures resulting from tectonic activity are investigated using this model. Fan deltas formed during periods of tectonic quiescence are shown to have a sheet-like form and grow mainly as a result of progradation. Topset development is limited, resulting in the development of oblique to sigmoidal clinoforms. Fan deltas formed during periods of tectonic activity have a more wedge-shaped form and are restricted to a region adjacent to the controlling fault. These fan deltas grow as a result of both progradation and aggradation, resulting in the development of sigmoidal clinoforms. Under conditions of constant tectonic subsidence and sediment supply, fan deltas are shown to undergo a brief period of progradation followed by aggradation and a long period of retrogradation. This is a consequence of an increasing amount of sediment being deposited as topset material as the delta progrades and the position of the offlap break being displaced basinward during hangingwall subsidence. Other controls on fan delta architecture, such as variations in sediment supply and sea/lake level, are also considered. Pleistocene-Recent, Gilbert-type fan deltas from the southern margin of the Gulf of Corinth rift, Greece contain many of the features described above and modelling is used to investigate whether it is possible to identify the controls on their sequence architectures.

Expression of human T cell receptor-gamma delta structural forms.

The human TCR-gamma delta occurs in three biochemically distinct forms (forms 1, 2bc, and 2abc). A 40-kDa TCR gamma-chain is disulfide-linked to the TCR delta-chain in form 1, whereas 40-kDa or 55-kDa TCR-gamma polypeptides are noncovalently associated with the TCR delta-chain in forms 2bc and 2abc, respectively. Sequence analysis of TCR-gamma cDNA clones indicates that form 1 utilizes the C gamma 1 gene segment, whereas forms 2bc and 2abc appear to use allelic C gamma 2 gene segments containing either two copies (b and c) or three copies (a, b, and c) of the CII exon, respectively. We transfected TCR-gamma cDNA encoding form 1 or form 2abc into the MOLT-13 cell line that expresses form 2bc. The transfected TCR gamma-chains associate with the resident MOLT-13 TCR-delta, normally part of form 2bc, to yield CD3-associated TCR-gamma delta heterodimers identical to those seen on the donor cell lines (form 1 or 2abc). These transfection experiments show directly that, 1) when a single TCR-delta subunit is available, the presence or absence of disulfide linkage between TCR gamma- and TCR delta-chains is controlled by the TCR gamma-chain, and 2) the difference in the amount of N-linked carbohydrate attached to the transfected TCR-gamma proteins of form 2bc vs form 2abc is influenced by the presence or absence of CII exon copy "a" which appears to alter the secondary and/or tertiary structure of these TCR gamma-chain constant regions, thereby affecting the attachment of N-linked glycans. In contrast to the similar structure and usage of C beta 1 and C beta 2, TCR-gamma delta forms show striking differences in structure and are not equally represented in peripheral blood. Although the role of each form is unknown, it is possible that variable or joining-gene segment selection events or functional differences account for their unequal usage.

Influence of surface area and additives on the thermal stability of transition alumina catalyst supports. II: Kinetic model and interpretation

The common features of the gamma, delta and theta forms of transition aluminas found in their structural and chemical properties allow them to be described by a unique formula, Al 2□O 3-v/2(OH) v < > 1-v/2 in which Al represents the aluminium ions in the trivalent sites, □ the cationic vacancies in the divalent sites, OH the hydroxyl groups substituting the oxygen in the normal positions of the anionic sublattice and < > the anionic vacancies of a spinel structure. This formula satisfies the conditions of electrical neutrality of the crystal, accounts for the required ratio of the number of sites in the structure and describes the range of stoichiometries from boehmite (v = 2) to alpha alumina (v = 0). Thus the incorporation of a foreign cation MZ +, either in an Al 3+ site or in a divalent vacancy, leads to a modification of the stoichiometry of different structural elements. The evolution of transition aluminas during thermal treatment consists of dehydroxylation by removal of water followed by an exothermic structural transformation to the alpha phase, which can be described in terms of an annihilation reaction between anionic and cationic vacancies. A theoretical model for spherical particeles based on the annihilation of vacancies as the rate-determining step leads to a kinetic law involving the initial specific surface area, the valency of the foreign cation, and a parameter which depends on its ionic radius. Kinetic data, previously reported for pure and various doped aluminas, agree satisfactorily with the theoretical law. The interest in and limitations of this model are discussed in relation to the experimental results.

Biogenesis of membrane-bound and secreted immunoglobulins: two primary translation products of the human delta chain, differentially N-glycosylated to four discrete forms in vivo and in vitro.

Structural differences between the heavy chain of membrane IgD (delta m) and the heavy chain of secreted IgD (delta s) were investigated by using a human lymphoblastoid cell line that expresses idiotypically identical IgM and IgD. In a wheat germ cell-free system, mRNA from this cell line was shown to encode two distinct delta chains that differed in molecular weight. When translated in vitro in the presence of dog pancreatic microsomal membranes or when synthesized in vivo, these two delta chains were processed to four discrete glycosylated forms, all of which shared idiotypic determinants, C region determinants, and light chain linkage. As shown by digestion with endo-beta-N-acetylglucosaminidase H, these four delta forms represent two delta polypeptide chains that are differentially N-glycosylated. Pulse-chase experiments demonstrated that, after endo-beta-N-acetylglucosaminidase H treatment, delta m has a higher molecular weight than delta s. After integration into dog pancreatic microsomal membranes in vitro, delta m was found not to have a large cytoplasmic domain exposed to proteolytic digestion. The finding that delta m and delta s differ in primary structure is analogous to previous work with the corresponding heavy chains of IgM (mu m and mu s) from the same cell line. Thus, this cell line produces four Ig heavy chains (mu m, mu s, delta m, and delta s), with the same idiotype. The observation of differential N-glycosylation, apparently unique for the delta class, is discussed.