1,827 research outputs found
A cell lineage analysis of segmentation in the chick embryo
We have studied the lineage history of the progenitors of the somite mesoderm and of the neural tube in the chick embryo by injecting single cells with the fluorescent tracer, rhodamine-lysine-dextran. We find that, although single cells within the segmental plate give rise to discrete clones in the somites to which they contribute, neither the somites nor their component parts (sclerotome, dermatome, myotome or their rostral and caudal halves) are `compartments' in the sense defined in insects. Cells in the rostral two thirds or so of the segmental plate contribute only to somite tissue and divide about every 10 h, while those in the caudal portions of this structure contribute both to the somites and to intermediate and lateral plate mesoderm derivatives. In the neural tube, the descendants of individual prospective ventral horn cells remain together within the horn, with a cycle time of 10 h.
We have also investigated the role of the cell division cycle in the formation and subsequent development of somites. A single treatment of 2-day chick embryos with heat shock or a variety of drugs that affect the cell cycle all produce repeated anomalies in the pattern of somites and vertebrae that develop subsequent to the treatment. The interval between anomalies is 6-7 somites (or a multiple of this distance), which corresponds to 10 h. This interval is identical to that measured for the cell division cycle. Given that cell division synchrony is seen in the presomitic mesoderm, we suggest that the cell division cycle plays a role in somite formation.
Finally, we consider the mechanisms responsible for regionalization of derivatives of the somite, and conclude that it is likely that both cell interactions and cell lineage history are important in the determination of cell fates
Digital herders and phase transition in a voting model
In this paper, we discuss a voting model with two candidates, C_1 and C_2. We
set two types of voters--herders and independents. The voting of independent
voters is based on their fundamental values; on the other hand, the voting of
herders is based on the number of votes. Herders always select the majority of
the previous votes, which is visible to them. We call them digital herders.
We can accurately calculate the distribution of votes for special cases. When
r>=3, we find that a phase transition occurs at the upper limit of t, where t
is the discrete time (or number of votes). As the fraction of herders
increases, the model features a phase transition beyond which a state where
most voters make the correct choice coexists with one where most of them are
wrong. On the other hand, when r<3, there is no phase transition. In this case,
the herders' performance is the same as that of the independent voters.
Finally, we recognize the behavior of human beings by conducting simple
experiments.Comment: 26 pages, 10 figure
Of Gold and Paper Money
We consider the role of money as a means of payment, store of value and medium of exchange. I outline a number of quantitative and qualitative experiences of monetary management. Successful regimes have sprung up in a variety of surprising places, and been sustained with state (centralised) interventions. Although the link between state and money, and its standard of identity and account may be clear, particularly in earlier stages of economic development, the extent to which the state is widely felt to hold responsibility for 'sound money' is less clear in modern democracies, where there are many other public responsibilities implying ongoing trade-offs
Quantisations of piecewise affine maps on the torus and their quantum limits
For general quantum systems the semiclassical behaviour of eigenfunctions in
relation to the ergodic properties of the underlying classical system is quite
difficult to understand. The Wignerfunctions of eigenstates converge weakly to
invariant measures of the classical system, the so called quantum limits, and
one would like to understand which invariant measures can occur that way,
thereby classifying the semiclassical behaviour of eigenfunctions. We introduce
a class of maps on the torus for whose quantisations we can understand the set
of quantum limits in great detail. In particular we can construct examples of
ergodic maps which have singular ergodic measures as quantum limits, and
examples of non-ergodic maps where arbitrary convex combinations of absolutely
continuous ergodic measures can occur as quantum limits. The maps we quantise
are obtained by cutting and stacking
Drivers and outcomes of work alienation: reviving a concept
This article sheds new light on an understudied construct in mainstream management theory, namely, work alienation.
This is an important area of study because previous research indicates that work alienation is associated with important
individual and organizational outcomes. We tested four antecedents of work alienation: decision-making autonomy, task
variety, task identity, and social support. Moreover, we examined two outcomes of alienation: deviance and performance, the
former measured 1 year after the independent variables were measured, and the latter as rated by supervisors. We present
evidence from a sample of 283 employees employed at a construction and consultancy organization in the United Kingdom.
The results supported the majority of our hypotheses, indicating that alienation is a worthy concept of exploration in the
management sciences
On the lease rate, convenience yield and speculative effects in the gold futures market
By examining data on the gold forward offered rate (GOFO) and lease rates over the period 1996- 2009, we conclude that the convenience yield of gold is better approximated by the lease rate than the interest-adjusted spread of Fama & French (1983). Using the latter quantity, we study the relationship between gold leasing and the level of COMEX discretionary inventory and exhibit that lease rates are negatively related to inventories. We also show that Futures prices have increasingly exceeded forward prices over the period, and this effect increases with the speculative pressure and the maturity of the contracts
A cell lineage analysis of segmentation in the chick embryo
We have studied the lineage history of the progenitors of the somite mesoderm and of the neural tube in the chick embryo by injecting single cells with the fluorescent tracer, rhodamine-lysine-dextran. We find that, although single cells within the segmental plate give rise to discrete clones in the somites to which they contribute, neither the somites nor their component parts (sclerotome, dermatome, myotome or their rostral and caudal halves) are `compartments' in the sense defined in insects. Cells in the rostral two thirds or so of the segmental plate contribute only to somite tissue and divide about every 10 h, while those in the caudal portions of this structure contribute both to the somites and to intermediate and lateral plate mesoderm derivatives. In the neural tube, the descendants of individual prospective ventral horn cells remain together within the horn, with a cycle time of 10 h.
We have also investigated the role of the cell division cycle in the formation and subsequent development of somites. A single treatment of 2-day chick embryos with heat shock or a variety of drugs that affect the cell cycle all produce repeated anomalies in the pattern of somites and vertebrae that develop subsequent to the treatment. The interval between anomalies is 6-7 somites (or a multiple of this distance), which corresponds to 10 h. This interval is identical to that measured for the cell division cycle. Given that cell division synchrony is seen in the presomitic mesoderm, we suggest that the cell division cycle plays a role in somite formation.
Finally, we consider the mechanisms responsible for regionalization of derivatives of the somite, and conclude that it is likely that both cell interactions and cell lineage history are important in the determination of cell fates
Consistency of the Shannon entropy in quantum experiments
The consistency of the Shannon entropy, when applied to outcomes of quantum
experiments, is analysed. It is shown that the Shannon entropy is fully
consistent and its properties are never violated in quantum settings, but
attention must be paid to logical and experimental contexts. This last remark
is shown to apply regardless of the quantum or classical nature of the
experiments.Comment: 12 pages, LaTeX2e/REVTeX4. V5: slightly different than the published
versio
Credibility and adjustment: gold standards versus currency boards
It is often maintained that currency boards (CBs) and gold standards (GSs) are alike in that they are stringent monetary rules, the two basic features of which are high credibility of monetary authorities and the existence of automatic adjustment (non discretionary) mechanism. This article includes a comparative analysis of these two types of regimes both from the perspective of the sources and mechanisms of generating confidence and credibility, and the elements of operation of the automatic adjustment mechanism. Confidence under the GS is endogenously driven, whereas it is exogenously determined under the CB. CB is a much more asymmetric regime than GS (the adjustment is much to the detriment of peripheral countries) although asymmetry is a typical feature of any monetary regime. The lack of credibility is typical for peripheral countries and cannot be overcome completely even by “hard” monetary regimes.http://deepblue.lib.umich.edu/bitstream/2027.42/40078/3/wp692.pd
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