562,609 research outputs found
Modeling Building Block Interdependency
No full textThe Building-Block Hypothesis appeals to the notion of problem decomposition and the assembly of solutions from sub-solutions. Accordingly, there have been many varieties of GA test problems with a structure based on building-blocks. Many of these problems use deceptive fitness functions to model interdependency between the bits within a block. However, very few have any model of interdependency between building-blocks; those that do are not consistent in the type of interaction used intra-block and inter-block. This paper discusses the inadequacies of the various test problems in the literature and clarifies the concept of building-block interdependency. We formulate a principled model of hierarchical interdependency that can be applied through many levels in a consistent manner and introduce Hierarchical If-and-only-if (H-IFF) as a canonical example. We present some empirical results of GAs on H-IFF showing that if population diversity is maintained and linkage is tight then the GA is able to identify and manipulate building-blocks over many levels of assembly, as the Building-Block Hypothesis suggests
Congenital heart block associated with Sjögren syndrome: case report
No full textBackground: Congenital heart block is a rare complication of pregnancy associated with Sjögren Syndrome that may result in the death of the foetus or infant, or the need for pacing in the newborn or at a later stage.Case report: The case is presented of a 64-year-old patient with primary Sjögren Syndrome and a history of having given birth to two sons with congenital heart block, both of whom required pacing several years later.Conclusion: The literature relating to this association is discussed including the suggested mechanism, long-term outcome of mothers of children with congenital heart block and preventive treatment strategies
A building-block Royal Road where crossover is provably essential
No full textOne of the most controversial yet enduring hypotheses about what genetic algorithms (GAs) are good for concerns the idea that GAs process building-blocks. More specifically, it has been suggested that crossover in GAs can assemble short low-order schemata of above average fitness (building blocks) to create higher-order higher-fitness schemata. However, there has been considerable difficulty in demonstrating this rigorously and intuitively. Here we provide a simple building-block function that a GA with two-point crossover can solve on average in polynomial time, whereas an asexual population or mutation hill-climber cannot
A simple two-module problem to exemplify building-block assembly under crossover
No full textTheoretically and empirically it is clear that a genetic algorithm with crossover will outperform a genetic algorithm without crossover in some fitness landscapes, and vice versa in other landscapes. Despite an extensive literature on the subject, and recent proofs of a principled distinction in the abilities of crossover and non-crossover algorithms for a particular theoretical landscape, building general intuitions about when and why crossover performs well when it does is a different matter. In particular, the proposal that crossover might enable the assembly of good building-blocks has been difficult to verify despite many attempts at idealized building-block landscapes. Here we show the first example of a two-module problem that shows a principled advantage for cross-over. This allows us to understand building-block assembly under crossover quite straightforwardly and build intuition about more general landscape classes favoring crossover or disfavoring it
G. Vernon Block
No full text"Pte G. Vernon Block VX150404 7th Battalion [11] Platoon "B" Coy 1939 - 1945. Dulcie Block (wife)".Private G. Vernon Block VX150404. 7th Battalion, [11] Platoon, "B" Company 1939 - 1945. Dulcie Block (wife)
Price impact of block trades in the Saudi stock market
No full textThis paper examines the price impact of block trades for the 124 companies that comprise all listed firms in the Saudi stock market (SSM). We use high frequency intraday data (one minute intervals) for the period 2005-2008 to provide out of sample evidence of the determinants of price impact. We find an asymmetric price impact of 0.5% for block purchases and -0.38% for block sales. We document a price continuation post block trades and a price reversal after block sales. Sellers of block trades in the Saudi market pay higher liquidity premiums than
buyers of block trades. However, on average, the price effect of a block trade is small and short-lived suggesting that resiliency is high in the market. Moreover, we find a direct relationship between the size of the trades and the level of information asymmetry in the market. Despite the structural differences of the SSM, the intraday pattern of price impacts is similar to patterns documented in other markets, namely an inverse J-shaped pattern. Finally,
sophisticated traders can gain abnormal profits in the SSM through “free riding”, a trader can benefit from the overreaction before the block trade and price reversal after the block trade
XLBlocks: a Block-based Formula Editor for Spreadsheet Formulas
No full textSpreadsheets are frequently used in industry to support critical business decisions. Unfortunately, they also suffer from error-proneness, which sometimes results in costly consequences. Experiments in the field of program education have shown that programmers tend to make fewer errors and can better focus on the logic of a program if they use a block-based language instead of a textual one. We hypothesize that a block-based formula editor could support spreadsheet users in a similar way. Therefore, we develop XLBlocks and conduct a think-aloud study with 13 experienced spreadsheet users from industry. Participants are asked to create and edit several formulas, using our block-based language. We then ask them to evaluate this editor using the Cognitive Dimensions of Notations framework. We found that for all dimensions the block-based formula editor received a better evaluation than the default text-based formula editor.Accepted author manuscriptSoftware Engineerin
A review of congenital heart block
No full textCongenital heart block is a rare disorder. It has an incidence of about 1 in 22,000 live
births. It may be associated with high mortality and morbidity. This should generate a
high index of suspicion for early diagnosis and aggressive therapy when appropriate.
The congenital heart block associated with neonatal lupus is considered a form of
passively acquired autoimmune disease in which maternal autoantibodies to the
intracellular ribonucleoproteins Ro (SS-A) and La (SS-B), cross the placenta and
injure the previously normal fetal heart. Women with serum titers of anti-Ro antibody
carry a 3% risk of having a child with neonatal lupus syndrome. Recurrence rates are
about 18%. We believe that serial echocardiograms should be acquired so that early
diagnosis is made and aggressive therapy administered, if signs of conduction
system disease such as PR interval prolongation by Doppler are found, so as to
optimize the outcome. Establishment of guidelines for therapy have been set
empirically, should signs of congenital heart block develop. Those patients whose
congenital heart block is associated with structural heart disease have a higher
morbidity and mortality, which is determined more by the underlying structural
congenital heart disease than it is by the need for a pacemaker per se.peer-reviewe
Price Impact of Block Trades and Price Behavior Surrounding Block Trades in Indian Capital Market
No full textWe analyze the permanent (information effect) and temporary (liquidity effect) impact of block trades transacted in the National Stock Exchange of India. Block trades are identified using multiple criteria based on trade value and trade volume. Overall, the permanent price impact is more for block purchases than for block sales indicating that block purchases are more informative than block sales, which may be motivated by liquidity need. Unlike in other markets, we observe that the temporary impact is greater than the permanent impact in case of block purchase. We classify the block trades as All-or-None (AON) and Not-AON trades depending on the number of transactions through which a block order is executed. As expected, the price impact is higher for Not-AON trades as compared to AON trades (which can be assumed to be pre-negotiated trades). Further, arrival of multiple block trades increases market confidence on the information. The permanent price impact is higher for days where there are more than one block trade of similar nature than for days with only one block trade. To analyze the speed of market response to the information associated with block trades, we have used the ‘transaction time event approach’, as used by Holthausen et al. (1990). We find that the prices start increasing (front running) 8 minutes before block purchases but not in case of block sales i.e. some information about the impending block purchase is factored in by the market when the block trade is for purchases. Further, in the case of block sales, prices revert quickly leaving very small permanent price impact.
Can market frictions really explain the price impact asymmetry of block trades? Evidence from the Saudi stock market
No full textWe empirically examine the price impact of block trades, in the Saudi Stock Market over
the time period of 2005-2008. Using a unique dataset of intraday data consisting of 2.3
million block buys and 1.9 million block sales, we find an asymmetry in the price impact of block purchases and sales. The asymmetry persists even when we account for the bidask bias in block trades, which is contrary to the previous literature. Overall, our findings suggest that in an emerging market where institutional trading is relatively scarce, market microstructure cannot explain the asymmetry in the price impact of large trades
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