Is an automatic alternation always a regular alternation?

2019 ◽  
Vol 89 ◽  
pp. 3-24
Author(s):  
Jin-Ho Lee
Keyword(s):  
Regular Alternation

Multidimensional structural variation in the cyanotrichite family of merotypes: camerolaite-3b-F\bar 1

2017 ◽  
Vol 73 (5) ◽  
pp. 950-955
Author(s):  
Stuart J. Mills ◽  
Andrew G. Christy ◽  
Georges Favreau ◽  
Valérie Galea-Clolus
Keyword(s):  
Short Range ◽  
Structural Variation ◽  
Unit Cell ◽  
Range Order ◽  
Phase Coupling ◽  
Unit Cell Parameters ◽  
Cell Parameters ◽  
Structural Variety ◽  
Group A ◽  
Regular Alternation

A new superstructure of the mineral camerolaite, Cu6Al3(OH)18(H2O)2[Sb(OH)6](SO4), has been refined in space groupP\bar 1 with unit-cell parametersaP= 7.7660 (16),bP= 8.759 (4),cP= 11.306 (2) Å, αP= 108.67 (4), βP= 83.41 (3), γP= 126.64 (2)°,V= 581.6 (3) Å3andZ= 1, withR1= 0.0951 (all data). This is the first refined example of a cyanotrichite-group mineral in which long-range order of interlayer anions produces a superstructure alongb, although diffuse scattering has previously been reported that corresponds to short-range order. Though the structure shares with other members of the cyanotrichite group a structural unit in which ribbons of edge-sharing Cu and Al octahedra form layers || (001), the superstructure arises from regular alternation of [SO4] and [Sb(OH)6] polyhedra along rods that lie between the layers, and phase coupling between rods that maximizes the distance between [SO4] groups of adjacent rods alongaandcdirections. This arrangement suggests an alternative nearly orthogonal choice of unit cell inF\bar 1 with parametersaF= 12.473 (26),bF= 8.759 (4),cF= 21.476 (7) Å, αF= 85.94 (4), βF= 95.91 (5), γF= 92.34 (9)°, which is recommended for comparing this structural variety of camerolaite with other members of the group.

scholarly journals Polymers with regular alternation of 1,7-bis[(dimethyl)silylmethylene]-m-carborane and diorganosiloxane units

2019 ◽  
Vol 488 (4) ◽  
pp. 383-385
Author(s):  
B. A. Izmaylov ◽  
V. A. Vasnev ◽  
G. D. Markova
Keyword(s):  
Organic Solvents ◽  
Amorphous Polymers ◽  
High Thermostability ◽  
Regular Alternation

New high-thermostable carboranylmethyl-containing diorganosiloxane polymers have been obtained by polycondensation of equimolar amounts of 1.7-bis[hydroxy(dimethyl)silylmethylene]-m-carborane with bis(dimethylamino)diorganosilanes. It was shown, that in the case of replacement of 24 to 33 mol. % of dimethylsiloxane units with methylphenylsiloxane or diphenylsiloxane units with bulk phenyl groups, only amorphous polymers are formed. The polymers are highly soluble in organic solvents and have high thermostability.

scholarly journals Notes on the metrical semantics of Russian, French and German imitations of Janus Secundus’s Basium II

2012 ◽  
Vol 40 (1/2) ◽  
pp. 155-176
Author(s):  
Igor Pilshchikov
Keyword(s):  
Nineteenth Century ◽  
Eighteenth Century ◽  
Regular Alternation

This article links Konstantin Batiushkov's poem Elysium (1810) to the tradition of poetic imitations of Janus Secundus's Basium II. A French equivalent for this poem's pythiambic distichs was invented by Ronsard (Chanson, 1578), who used cross-rhymed quatrains with regular alternation of dodecasyllabic and hexasyllablic lines. However, the French translators of Basia of the eighteenth and early nineteenth centuries could not use this metre, because its semantic aura was drastically changed by Malherbe's Consolation à Monsieur du Périer (1598). Batiushkov's Elysium as well as its Latin and French sources are poems about a delightful death and the union of lovers in the afterlife; yet the metre, which was used in Malherbe's poem, was for more than two centuries a metre of mournful elegiac stanzas about eternal separation. The question of a metrical prototype for Batiushkov's poem still remains undetermined. His "anacreontic" trochaic tetrameter does not have analogues in the Latin original or its French translations, but coincides with the metre of G. A. Bürger's Die Umarmung from 1776 (of which Batiushkov was hardly aware in 1810), and finds parallels in some eighteenth-century Russian imitations of Basium II which were most likely forgotten by the beginning of the nineteenth century.

VI.—Ovarian Rhythm in Drosophila

1938 ◽  
Vol 57 ◽  
pp. 78-96 ◽  
Author(s):  
H. P. Donald ◽  
Rowena Lamy
Keyword(s):  
Drosophila Melanogaster ◽  
Regular Alternation

While observations were being carried out on the fecundity of certain experimental Drosophila pseudo-obscura females, it became apparent that there was a regular alternation of periods of rapid laying with periods of no laying. Since an irregularity in rate of oviposition in this species had been noticed by other investigators, and since, under similar circumstances, Drosophila melanogaster lays approximately the same number of eggs each day, it was decided to investigate more closely the possibility that differences in laying habit existed among the various species.

scholarly journals Кристаллографические особенности структуры alpha-фазы гафния и сплавов гафний--титан

2019 ◽  
Vol 89 (1) ◽  
pp. 86
Author(s):  
Ю.В. Хлебникова ◽  
Д.П. Родионов ◽  
Л.Ю. Егорова ◽  
Т.Р. Суаридзе
Keyword(s):  
Polymorphic Transformation ◽  
Mixed Structure ◽  
Cast State ◽  
Β Phase ◽  
Ti Alloys ◽  
Α Phase ◽  
Phase Crystal ◽  
Lath Crystals ◽  
Crystallographic Orientations ◽  
Regular Alternation

AbstractThe structure of a hafnium crystal undergoing β → α (bcc → hcp) polymorphic transformation upon gradual cooling and the structure of Hf_55Ti_45 and Hf_30Ti_70 alloys formed under various kinetic conditions of polymorphic transformation are studied. The structure of the α phase in cast hafnium is shown to consist of lath crystals grouped into packets. The misorientations between separate laths in a packet are less than 1°. The Hf–Ti alloys in the cast state exhibit a mixed structure consisting of α-phase crystals of several morphological types. A structure of packet martensite is observed in the Hf–Ti alloys after quenching. Each packet includes laths of several crystallographic orientations. There is no regular alternation of differently orientated laths in the packet. The same set of α-phase orientations within an initial β-phase grain is observed independently of the cooling rate of the Hf–Ti alloys upon β → α polymorphic transformation. The misorientation of substructural elements within an α-phase crystal in the Hf–Ti alloys is ~5° for the cast state and ~2.2° after quenching.

Studies on the non-parasitic stages of the cattle tick, Boophilus microplus (Canestrini) (AcarinaL Ixodidae)

1955 ◽  
Vol 3 (3) ◽  
pp. 295 ◽  
Author(s):  
LF Hitchcock
Keyword(s):  
Relative Humidity ◽  
Water Loss ◽  
Boophilus Microplus ◽  
Cattle Tick ◽  
Laboratory Studies ◽  
Water Losses ◽  
Cent Relative Humidity ◽  
Saturated Atmosphere ◽  
Effects Of Temperature ◽  
Regular Alternation

Laboratory studies of the effects of temperature and relative humidity on the non-parasitic stages of the cattle tick, Boophilus microplus (Canestrini), are described. The pre-oviposition period ranged from 19-39 days at 59-60�F to 2-3 days at 97�F. The duration of oviposition was uninfluenced by relative humidity but varied from a maximum of 44 days at 59�F to a minimum of 4 days at 102�F. The minima at each temperature were exceedingly irregular, due to the deaths of ticks. The number of eggs laid by a female tick was uninfluenced by relative humidity. The peak oviposition mean of 2496 eggs per female occurred at 75�F, fewer eggs being laid at higher and lower temperatures. Daily egg output attained a maximum of 197 at 92�F, but was uninfluenced by relative humidity. The water loss of engorged female ticks was greatly affected by inert dusts and even dusting with a sample of soil chosen at random produced a significant increase in water loss. Developmental period was uninfluenced by order of deposition, but percentage hatch of eggs laid during the last few days of oviposition is lower. Eggs did not hatch at constant relative humidities lower than 70 per cent., but some were able to survive relative humidities lower than this if exposed periodically to a saturated atmosphere. The period of development of eggs varied from a maximum of 146 days at 62�F to a minimum of 14 days at 97�F. Maximum hatch occurred between 85 and 95�F, and at relative humidities above 95 per cent. Exposure of eggs to temperatures below the developmental zero prolonged the period of development merely by the period of exposure. Regular alternation of temperature between the limiting temperatures of 59 and 97�F with a steady rise or fall between the extremes resulted in development at a rate approximately equal to that obtained at constant temperature of 78�F, the arithmetic mean of the above figures. Larval longevity was influenced markedly by temperature and humidity. A maximum of 240 days was recorded at 72�F and 90 per cent. relative humidity. Larvae are able to recoup water losses sustained at low relative humidity by absorption from the atmosphere during subsequent periods of high relative humidity.

scholarly journals Distinct Contributions of the Magnocellular and Parvocellular Visual Streams to Perceptual Selection

2012 ◽  
Vol 24 (1) ◽  
pp. 246-259 ◽  
Author(s):  
Rachel N. Denison ◽  
Michael A. Silver
Keyword(s):  
Visual System ◽  
Binocular Rivalry ◽  
Visual Processing ◽  
Neural Substrates ◽  
Hierarchical Organization ◽  
Neural Basis ◽  
Multiple Stimulus ◽  
Perceptual Alternation ◽  
New Framework ◽  
Regular Alternation

During binocular rivalry, conflicting images presented to the two eyes compete for perceptual dominance, but the neural basis of this competition is disputed. In interocular switch rivalry, rival images periodically exchanged between the two eyes generate one of two types of perceptual alternation: (1) a fast, regular alternation between the images that is time-locked to the stimulus switches and has been proposed to arise from competition at lower levels of the visual processing hierarchy or (2) a slow, irregular alternation spanning multiple stimulus switches that has been associated with higher levels of the visual system. The existence of these two types of perceptual alternation has been influential in establishing the view that rivalry may be resolved at multiple hierarchical levels of the visual system. We varied the spatial, temporal, and luminance properties of interocular switch rivalry gratings and found, instead, an association between fast, regular perceptual alternations and processing by the magnocellular stream and between slow, irregular alternations and processing by the parvocellular stream. The magnocellular and parvocellular streams are two early visual pathways that are specialized for the processing of motion and form, respectively. These results provide a new framework for understanding the neural substrates of binocular rivalry that emphasizes the importance of parallel visual processing streams, and not only hierarchical organization, in the perceptual resolution of ambiguities in the visual environment.

O2 and CO2 transport in relation to ventilation in the Atlantic mackerel, Scomber scombrus

1984 ◽  
Vol 62 (4) ◽  
pp. 546-554 ◽  
Author(s):  
R. G. Boutilier ◽  
P. Aughton ◽  
G. Shelton
Keyword(s):  
Major Change ◽  
Blood Oxygenation ◽  
Dominant Negative ◽  
Positive Pressure ◽  
Forward Movement ◽  
Atlantic Mackerel ◽  
Arterial Blood ◽  
Ram Ventilation ◽  
Pressure Phase ◽  
Regular Alternation

Adult mackerel actively ventilate their gills whilst swimming at low speeds (20–60 cm∙s−1; ca. 0.6–2.0 body lengths∙s−1) in a swim tunnel at 15 °C. There was a regular alternation of a buccal pump, with dominant positive pressure phase, and an opercular pump, with dominant negative pressure phase. The two pumps cooperated to produce a maintained differential pressure across the gills (buccal to opercular cavities) so that water would flow in this direction for most, if not all, of the respiratory cycle. At swimming velocities between 60 and 80 cm∙s−1 (2.0–2.6 body lengths∙s−1), mackerel were found to suspend their cyclic buccal–opercular pump and rely instead on ventilation of the gills by forward movement through the water column (ram ventilation). The transition from one type of ventilation to the other caused no major change in the oxygenation of arterial blood, though CO2 was eliminated readily at the higher swimming speeds despite its being produced in larger quantities. Variations in arterial acid–base relationships were largely due to the mackerel's response to capture and subsequent experimental procedures, and not to the change from cyclic to ram ventilation. It is concluded that arterial blood oxygenation and CO2 output are regulated within limits that suggest the gills are adequately ventilated at all swimming speeds.

The crystal structure of dalnegroite, Tl5−xPb2x(As,Sb)21−xS34: a masterpiece of structural complexity

2010 ◽  
Vol 74 (6) ◽  
pp. 999-1012 ◽  
Author(s):  
L. Bindi ◽  
F. Nestola ◽  
A. Guastoni ◽  
L. Secco
Keyword(s):  
Crystal Structure ◽  
Structural Complexity ◽  
Unit Cell ◽  
Layered Compound ◽  
Chemical Compositions ◽  
Isotropic Model ◽  
Triclinic Space Group ◽  
Space Group ◽  
Regular Alternation

AbstractThe crystal structure of the rare mineral dalnegroite, Tl5−xPb2x(As,Sb)21−xS34with x ≈ 1, was determined for a crystal from Lengenbach, Binn Valley, Switzerland. The structure is triclinic, space group P1, witha= 16.218(3),b= 42.546(7),c= 8.558(1) Å , α = 95.70(4), β = 90.18(3), γ = 96.38(4)°,V= 5838.9(9) Å3, Z = 4. Refinement of an isotropic model led to an R1index of 0.0536 for 22226 observed reflections and 980 parameters, and R1= 0.0590 for all 25266 independent reflections. Although dalnegroite cannot be considered a layered compound, its structure can be usefully described as a regular alternation of two kinds of layers stacked along thebaxis, with four layers in the unit cell: (1) a layer 7.8 Å thick, at y ≈ 0.15 and 0.65, can be considered as derived from the SnS archetype; (2) a layer 13.6 Å thick, at y ≈ 0.35 and 0.85, derived from the PbS archetype. Different chemical compositions, such as Tl:Pb and Sb:As ratios, for different samples belonging to the chabournéite-dalnegroite family could play a central role in controlling different degrees of order, leading to different superstructures.

scholarly journals Synthesis of 1,1,3,3,5,5-Hexamethyl-7,7-diorganocyclotetrasiloxanes and Its Copolymers

Polymers ◽  
2021 ◽  
Vol 14 (1) ◽  
pp. 28
Author(s):  
Evgeniya V. Talalaeva ◽  
Aleksandra A. Kalinina ◽  
Evgeniy V. Chernov ◽  
Alina G. Khmelnitskaia ◽  
Marina A. Obrezkova ◽  
...  
Keyword(s):  
Reaction Conditions ◽  
Preparative Yield ◽  
Linear Poly ◽  
Regular Alternation

This paper reports a method for the synthesis of 1,1,3,3,5,5-hexamethyl-7,7-diorganocyclotetrasiloxanes by the interaction of 1,5-disodiumoxyhexamethylsiloxane with dichlorodiorganosilanes such as methyl-, methylvinyl-, methylphenyl-, diphenyl- and diethyl dichlorosilanes. Depending on the reaction conditions, the preparative yield of the target cyclotetrasiloxanes is 55–75%. Along with mixed cyclotetrasiloxanes, the proposed method leads to the formation of polymers with regular alternation of diorganosylil and dimethylsylil units. For example, in the case of dichlorodiethylsilane, 70% content of linear poly(diethyl)dimethylsiloxanes with regular alternation of units can be achieved in the reaction product. Using 7,7-diethyl-1,1,3,3,5,5-hexamethylcyclotetrasiloxane as an example, the prospects of the mixed cycle in copolymer preparation in comparison with the copolymerization of octamethyl- and octaethylcyclotetrasiloxanes are shown.

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