Bipolar orientation

Motor protein-mediated Interactions between opposing polar microtubules and between asters and the cell cortex align and separate the centrosomes at prophase, establishing the bipolar orientation of the spindle (see Figure 20-34). 

Textures correspond to various arrangements of defects. When the isotropic liquid is cooled, the nematic phase may appear at the deisotropization point in the form of separate small, round objects called droplets (Fig. 12). These can show extinction crosses, spiral structures, bipolar arrangements, or some other topology depending on boundary conditions. Theoretical studies based on a simple model confirm the stability of radial or bipolar orientation (Fig. 5) [22]. Considerations based on improved theoretical models yield stable twisted... 

Fig. 11. Semidiagrammatic representation of orientation at meiotic prometaphase I. Four bivalents, each composed of two chromosomes (half-bivalents) are shown with their chromosomal spindle fibers (broken lines). Three bivalents (above) are shown in bipolar orientation in each, the partner half-bivalents are oriented to opposite poles. One bivalent (below) is shown In unipolar malorientation. Both half-bivalents are oriented to the lower pole (the arrow Indicates the direction of artificial force applied in tension experiments described below. (From Nicklas and Koch. 1969. J. Cell Biol., 43 40-50.)...

This suggests that controlled distribution depends upon two processes, each of which requires explanation. First, for some reason the initial orientation is so ordered that the vast majority of all chromosomes achieve bipolar orientation directly and immediately in early prometaphase. Second, however, malorientations do occur and for some reason are almost invariably followed by reorientation and the indirect achievement of bipolar orientation. 

The proportion of bivalents that achieve bipolar orientation in this fashion will doubtless vary in cells from different organisms. Thus the proportion may be lowered if long bivalents occur and their interkinetochoric chromatin is flexible. Such bivalents are often observably flexed between the kinetochores of partner half-bivalents, which are therefore not constrained to face in opposite directions. As expected from the present interpretation of initial orientation, these bivalents malorient abnormally often (Ostergren, 1951, pp. 140 ff White, 1961 Henderson et al., 1970). Conversely, in cells where individual spindles form around each chromosome and are oriented to each... 

Fig. 13. Repeated experimental induction of unipolar malorientation in one bivalent of a living grasshopper Melanopius differentiaHs) spermatocyte. The kinetochoric ends of the micromanipulated bivalent are identified by numbered arrows, and the time in minutes is indicated on each print. The micromanipulation needle was removed from the cell after each induction of unipolar orientation (25, 33.6, 52, and 157 minutes), and natural reorientations to the normal bipolar orientation followed in every case (33.0, 40.0, 94, and 211 minutes). A normal anaphase ensued (263, 284 minutes). Details In the text. XI,000. (From Nicklas. 1967. Chromosoma, 21 17-50.)...

Figure 11. The object was to stretch the bivalent to approximately the same degree as occurs naturally in bipolar orientations. The same bivalent could, earlier or later, be used for control experiments with the needle nearby but not stretching the bivalent. The results from eight bivalents in eight cells are clear-cut a total of 311 minutes under artificial tension was accumulated without a single reorientation—each bivalent remained in unipolar orientation—while the controls reoriented in an average of 15.7 minutes. The tension clearly stabilized an orientation highly unstable in its absence.

The conclusion (Nicklas and Koch, 1969) is that tension on bivalents and their spindle fibers, or some consequence of tension, makes orientations stable. Since under natural conditions such tension is limited to the bipolar orientation, this is sufficient to explain accumulation of appropriate orientations as prometaphase procedes. This explanation is not as secure as that for initial orientation, however. The present evidence is certainly dramatic, but it all derives from formally identical experiments. So far, for instance, the reciprocal experiment of inducing / stability through relaxation of natural tension has not been unambiguously successful (Nicklas and Koch, 1969). Moreover, some possible alternatives (see especially Bauer et al., 1961, pp. 181-182 on lateral interactions) have not been eliminated although they offer no obvious explanation for the effect of tension. 

A. Most bivalents achieve bipolar orientation immediately because 1. individual half-bivalents tend to orient to the pole they most nearly face and 2. chromosome structure is such that if one half-bivalenf s kinetochores face one pole, those of its partner face the opposite pole. 

B. But mistakes do occur, and unipolar orientations result. These are rectified by reorientation which occurs and recurs until the uniquely stable bipolar orientation results. This stability derives from oppositely directed spindle forces that produce tension. 

C. Bipolar orientations established in prometaphase-metaphase produce segregation to opposite poles in anaphase and thus an equipartition of half-bivalents between the daughter cells. 

Wherever reorientation is an essential feature of mitosis, it probably has the same cause as in meiosis, although direct evidence is lacking (Nicklas and Koch, 1969). Thus, appropriate bipolar orientation subjects the mitotic chromosome to oppositely directed forces (cf. the deformations observed by Bajer, 1958a, Fig. 6). By analogy with meiosis, the resultant tension directly or indirectly stabilizes these orientations, and reorientation occurs until this state is reached. 

Exactly this is observed in studies on fixed cells (reviewed by John and Lewis, 1965, pp. 52ff.) and following experimental destruction of the linkage by micromanipulation of living cells (Nicklas, unpublished). A more exact prediction is possible from the postulated role of bipolar tension in reorientation unpaired meiotic chromosomes that retain the meiotic synorientation of both sister kinetochores to the same pole should be unstable and frequently reorient. If, however, they achieve amphiorientation, as do mitotic chromosomes, a stable bipolar orientation should result. Both conditions occur in nature and with the expected result (living cells with unpaired sex chromosomes, Dietz, 1956 Bauer et al., 1961 Nicklas, 1961 fixed cells, reviewed by John and Lewis, 1965). 

Another eonsideration is the type of pass unit to be used. From a headroom loss standpoint, it makes absolutely no differenee whether a bipolar power transistor or a power MOSFET is used. The differenee eomes in the drive eireuitry. If the headroom voltage is high, the eontroller (usually a ground-oriented eireuit) must pull eurrent from the input or output voltage to ground. For a single bipolar pass transistor this eurrent is... 

FIGURE 4.15 Cross-section of multilevel interconnections for advanced bipolar devices. Fourteen separate layers are laid down in the fabrication of interconnections such as the one shown. The precise orientation and composition of these layers are controlled by chemical process steps. Copyright 1982 by the International Business Machines Corporation. Reprinted with permission. 

Two types of EDL are distinguished superficial and interfacial. Superficial EDLs are located wholly within the surface layer of a single phase (e.g., an EDL caused by a nonuniform distribution of electrons in the metal, an EDL caused by orientation of the bipolar solvent molecules in the electrolyte solution, an EDL caused by specific adsorption of ions). Tfie potential drops developing in tfiese cases (the potential inside the phase relative to a point just outside) is called the surface potential of the given phase k. Interfacial EDLs have their two parts in dilferent phases the inner layer with the charge density in the metal (because of an excess or deficit of electrons in the surface layer), and the outer layer of counterions with the charge density = -Qs m in the solution (an excess of cations or anions) the potential drop caused by this double layer is called the interfacial potential... 

Loss of sister chromatid cohesion would therefore be sufficient for the sudden movement of chromatids to opposite poles at the metaphase to anaphase transition. According to this hypothesis, a specific apparatus binds chromatids together during replication, holds them in an orientation that facilitates the attachment of sister kinetochores to spindles extending to opposite poles, and resists the splitting force that results from this bipolar attachment to the spindle. Destruction of this specialized cohesive structure triggers movement of chromatids to opposite poles at the onset of anaphase. 

Furthermore, clinical trials are performed in various cultural and geographical settings. Transcultural differences may play a significant role in drug efficacy e.g. oriental populations require much lower doses of antipsychotic drugs compared with Caucasian patient populations. Phase IV trials also may be performed to explore possible novel uses for compounds approved and marketed in other indications (e.g. treatment of anxiety disorders with antidepressants, treatment of bipolar disorder with anticonvulsants, etc.). 

For bipolar organic liquids, especially for hydrogen-bonding liquids such as alcohols and amines, the tendency to orient in the liquid phase, due to these highly directional intermolecular attractions, is greatly increased by this intermolecular interaction. We can see the effect of this in the significantly larger entropies of vaporization of bipolar chemicals, like aniline, phenol, benzyl alcohol, or ethanol (Table 4.2). 

With current instruments it is possible to make spatial maps of the emission from different species in the Red Rectangle. These maps might provide valuable clues to the origin of different spectroscopic features. For example, in the spectrum of the Red Rectangle, the emission features which correspond to the diffuse interstellar bands are concentrated in what appears to be two hollow cones oriented perpendicular to the plane of this bipolar system (Schmidt Witt 1991). This hollow cone is similar to that proposed by Jura Kroto (1990) to explain the observed (Nguyen-Q-Rieu et al. 1986) HC,N emission (see around AFGL 2688, the Egg Nebula ), a very well studied carbon-rich object that appears to be in transition from a red giant to a planetary nebula. 

We will now dwell on relaxation processes. Since we intend to discuss only relaxation which is isotropic with respect to orientations of J, its probability depends only on the angle 0 between the initial 0, p and the final 0,

bipolar harmonics [379] in the form... 

The operation of the SPICE design is closely analogous to that of a conventional bipolar transistor comprising distinct emitter, base, and collector stages but with some differences that are forced by materials considerations. The central base layer is a doped semiconductor and in it is established a non-equilibrium minority carrier population by injection from the emitter. Additionally these injected carriers are partly spin polarized and when they are harvested by the spin-dependent collector, the collection efficiency is dependent on the relative orientations of the emitter and collector orientations. The feasibility of these devices depend on several issues,... 

In 2005, the pharmaceutically oriented Journal of the American Academy of Child and Adolescent Psychiatry published guidelines for the diagnosis and treatment of bipolar disorder (Kowatch et al., 2005). Martha Hel-lander, a coauthor of the guidelines, declared, These kids suffer so badly, and deserve to have evidence-based treatment as early in life as possible. Many respond quickly to mood stabilizing medication. ... 

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