Discrete Group Actions on Spacetimes: Causality Conditions and the Causal Boundary

Suppose a spacetime $M$ is a quotient of a spacetime $V$ by a discrete group of isometries. It is shown how causality conditions in the two spacetimes are related, and how can one learn about the future causal boundary on $M$ by studying structures in $V$. The relations between the two are particularly simple (the boundary of the quotient is the quotient of the boundary) if both $V$ and $M$ have spacelike future boundaries and if it is known that the quotient of the future completion of $V$ is past-distinguishing. (That last assumption is automatic in the case of $M$ being multi-warped.)Comment: 32 page

Stable and unstable regimes in Bose-Fermi mixture with attraction between components

A collapse of the trapped boson- fermion mixture with the attraction between bosons and fermions is investigated in the framework of the effective Hamiltonian for the Bose system. The properties of the $^{87}$Rb and $^{40}$K mixture are analyzed quantitatively at $T= 0$. We find numerically solutions of modified Gross- Pitaevskii equation which continuously go from stable to unstable branch. We discuss the relation of the onset of collapse with macroscopic properties of the system. A comparison with the case of a Bose condensate of atomic $^7Li$ system is given.Comment: 7 pages, 5 figure

Ten popular myths concerning the employment of labour in Rhodesia

A RJE article on labour and employment regulations in the then Rhodesia (now Zimbabwe)For the purposes of this paper I will define a “myth” as a purely fictitious narrative embodying popular ideas on natural phenomena. Economics is the sort of subject that lends itself to the creation of myths in order to “explain” or “predict” the nature of the relationship between economic variables. It is my intention in this paper to draw attention to the purely fictitious nature of ten popular beliefs that constantly cloud the issues associated with the employment of labour in Rhodesia

Regression and Inertia in the the Rhodesian Fiscal Structure— a Comment on the 1972 Budget

An analysis of the Rhodesian budget statement of 1972.It is my intention in this paper to comment on the structure of the budget and on Rhodesian fiscal policy in the light of this budgetary structure. I have two basic observations to make. The first is that the 1972 budget is, in structural terms, entirely as was to be expected and it may, in fact, be interpreted as one further budget which has the effect of maintaining a gradual but consistent regressive shift in the fiscal structure. The second is that the structure is not only regressive, but also fairly rigid, and the budgetary principles that have formed the basis of not only this, but also a succession of budgets prior to this, have had the net effect of reducing the impact of fiscal policy on the general level of economic activity. This second observation should not be interpreted as implying a reduction in the influence of the state in the economy but rather as an implication that other, non-fiscal methods, have been increasingly employed in an effort to achieve desired objectives. Generalisations, by definition, seek to simplify complex situations by reference to dominant characteristics. The test of validity, when applied to generalisations, is not whether simplification obscures detail, but whether this suppression of detail is in fact misleading. My basic thesis is that discussion and analysis of the Rhodesian budget is very often concerned with detail, to the extent that general principles are often overlooked. Further, the details themselves are carefully woven into the general fabric of this structure, and thus an overview is the most efficient way of gaining an insight into the detail

An Innovative Approach to Achieve Compositionality Efficiently using Multi-Version Object Based Transactional Systems

In the modern era of multicore processors, utilizing cores is a tedious job. Synchronization and communication among processors involve high cost. Software transaction memory systems (STMs) addresses this issues and provide better concurrency in which programmer need not have to worry about consistency issues. Another advantage of STMs is that they facilitate compositionality of concurrent programs with great ease. Different concurrent operations that need to be composed to form a single atomic unit is achieved by encapsulating them in a single transaction. In this paper, we introduce a new STM system as multi-version object based STM (MVOSTM) which is the combination of both of these ideas for harnessing greater concurrency in STMs. As the name suggests MVOSTM, works on a higher level and maintains multiple versions corresponding to each key. We have developed MVOSTM with the unlimited number of versions corresponding to each key. In addition to that, we have developed garbage collection for MVOSTM (MVOSTM-GC) to delete unwanted versions corresponding to the keys to reduce traversal overhead. MVOSTM provides greater concurrency while reducing the number of aborts and it ensures compositionality by making the transactions atomic. Here, we have used MVOSTM for the list and hash-table data structure as list-MVOSTM and HT- MVOSTM. Experimental results of list-MVOSTM outperform almost two to twenty fold speedup than existing state-of-the-art list based STMs (Trans-list, Boosting-list, NOrec-list, list-MVTO, and list-OSTM). HT-MVOSTM shows a significant performance gain of almost two to nineteen times better than existing state-of-the-art hash-table based STMs (ESTM, RWSTMs, HT-MVTO, and HT-OSTM). MVOSTM with list and hash-table shows the least number of aborts among all the existing STM algorithms. MVOSTM satisfies correctness-criteria as opacity.Comment: 35 pages, 23 figure

Inclination-Independent Galaxy Classification

We present a new method to classify galaxies from large surveys like the Sloan Digital Sky Survey using inclination-corrected concentration, inclination-corrected location on the color-magnitude diagram, and apparent axis ratio. Explicitly accounting for inclination tightens the distribution of each of these parameters and enables simple boundaries to be drawn that delineate three different galaxy populations: Early-type galaxies, which are red, highly concentrated, and round; Late-type galaxies, which are blue, have low concentrations, and are disk dominated; and Intermediate-type galaxies, which are red, have intermediate concentrations, and have disks. We have validated our method by comparing to visual classifications of high-quality imaging data from the Millennium Galaxy Catalogue. The inclination correction is crucial to unveiling the previously unrecognized Intermediate class. Intermediate-type galaxies, roughly corresponding to lenticulars and early spirals, lie on the red sequence. The red sequence is therefore composed of two distinct morphological types, suggesting that there are two distinct mechanisms for transiting to the red sequence. We propose that Intermediate-type galaxies are those that have lost their cold gas via strangulation, while Early-type galaxies are those that have experienced a major merger that either consumed their cold gas, or whose merger progenitors were already devoid of cold gas (the ``dry merger'' scenario).Comment: Accepted for publication in ApJ. 7 pages in emulateap

Liquidity measures and cost of trading in an illiquid market

We provide the first in-depth study of trading on the Ukrainian stock exchange, using trade-by-trade data. Although Ukraine has some large listed companies, the market is quite illiquid. We study the efficiency of five liquidity measures in the market. The proportion of no-trading days is the most reliable of the five, while turnover, which is widely used in the literature, is a poor measure. On trading cost, trades in all size categories are executed within the quoted spread, as in other dealership markets, with medium-sized trades being the cheapest. The cost of sales is higher than the cost of purchases under all market conditions