Engineering Practical Lempel-Ziv Tries

The Lempel-Ziv 78 ( LZ78 ) and Lempel-Ziv-Welch ( LZW ) text factorizations are popular, not only for bare compression but also for building compressed data structures on top of them. Their regular factor structure makes them computable within space bounded by the compressed output size. In this article, we carry out the first thorough study of low-memory LZ78 and LZW text factorization algorithms, introducing more efficient alternatives to the classical methods, as well as new techniques that can run within less memory space than the necessary to hold the compressed file. Our results build on hash-based representations of tries that may have independent interest.

Superspreading as a Regular Factor of the COVID-19 Pandemic: II. Quarantine Measures and the Second Wave

Within the framework of a two-component model of the COVID-19 epidemic, taking into account the special role of superspreaders, we consider the impact of the recovery factor and quarantine measures on the course of the epidemic, as well as the possibility of a second wave of morbidity. It is assumed that there is no long-term immunity in asymptomatic superspreaders who have under- gone the infection, and the emergence of long-term immunity in those who have undergone severe illness. It is shown that, under these assumptions, the relaxation of quarantine measures leads to the resumption of virus circulation among asymptomatic superspreaders. Depending on the charac- teristics of the quarantine, its removal may or may not lead to a renewed wave of daily morbidity. A criterion for the occurrence of repeated wave of morbidity is proposed based on the analysis of the final phase of the first wave. Based on this criterion, the repeated wave of the epidemic is predicted in New Zealand. A natural explanation is given for the decrease in lethality among the infected against the background of an absolute increase in their number.

Superspreading as a Regular Factor of the COVID-19 Pandemic

An impact of superspreading on the course of the COVID-19 epidemic is considered. A two-component model of the epidemic has been developed, in which all infected are divided in two groups. They are asymptomatic superspreaders spreading the infection and sensitive persons which can only get infection. Once infected the sensitive exhibit clear symptoms and become isolated. Taking into account both factors allows find the numbers of superspreaders and sensitive persons. It is shown, that the ratio of increment of the number of daily cases in the beginning of the epidemic and decrement at the end of the epidemic is equal to the ratio of numbers of the superspreaders and sensitive persons. In this way, on the base of data from 12 countries and territories, the share of asymptomatic among all infected persons is found to be (17 ± 3) %. Specific measures to limit the epidemical incidence are proposed. The possibility of an allergic component in the disease is discussed.

Use of arteriovenous fistula in children with bleeding disorders

Haemophilia and associated bleeding disorders are chronic conditions that require easy, accessible, and reliable venous access for treatment. Peripheral venous access is traditionally the first option considered for prophylaxis. The initial introduction of prophylaxis to a child is during the first two years of life, and peripheral access can be problematic. Central venous catheters (CVC), for example port-a-caths, are widely used among this group; however, these devices require surgical insertion and are not without their own complications. Data were collected on venous access methods used at the paediatric centre at the Evelina London Children’s Hospital, where 242 children are registered at the comprehensive care centre, 48 of whom have a severe bleeding disorder. Of these 48, 27 have a CVC currently (PICC n=1, Port-a-Cath n=25, Hickman line n=1) and 3 have an arteriovenous fistula (AVF). Patient 1 is a 12 year-old boy with severe haemophilia A and an intracranial haemorrhage at the age of 9 months. He remains on prophylaxis and had an AVF created 5 years ago following repeated port-a-cath infections and poor venous access. Patient 2 is a 7 year-old boy with severe haemophilia B and an inhibitor, who has also had repeated port-a-cath infections. An AVF was constructed 2 years ago. Patient 3 is a 12 year-old girl with type III von Willebrand disease and an inhibitor. Due to need for regular factor treatment in the context of poor venous access, an AVF was formed. We have had a 100% success rate with all three AVFs at a follow-up period of 8-69 months. Our experience suggests AVF is a viable option of venous access in patients with haemophilia and other bleeding disorders, especially so for children with repeated CVC infections or poor peripheral venous access. However, this is not a straightforward option and further evidence on long-term use based on multicentre research will be beneficial in managing AVF in this group of patients.

Algorithms for Sparse Nonnegative Tucker Decompositions

There is a increasing interest in analysis of large-scale multiway data. The concept of multiway data refers to arrays of data with more than two dimensions, that is, taking the form of tensors. To analyze such data, decomposition techniques are widely used. The two most common decompositions for tensors are the Tucker model and the more restricted PARAFAC model. Both models can be viewed as generalizations of the regular factor analysis to data of more than two modalities. Nonnegative matrix factorization (NMF), in conjunction with sparse coding, has recently been given much attention due to its part-based and easy interpretable representation. While NMF has been extended to the PARAFAC model, no such attempt has been done to extend NMF to the Tucker model. However, if the tensor data analyzed are nonnegative, it may well be relevant to consider purely additive (i.e., nonnegative) Tucker decompositions). To reduce ambiguities of this type of decomposition, we develop updates that can impose sparseness in any combination of modalities, hence, proposed algorithms for sparse nonnegative Tucker decompositions (SN-TUCKER). We demonstrate how the proposed algorithms are superior to existing algorithms for Tucker decompositions when the data and interactions can be considered nonnegative. We further illustrate how sparse coding can help identify what model (PARAFAC or Tucker) is more appropriate for the data as well as to select the number of components by turning off excess components. The algorithms for SN-TUCKER can be downloaded from Mørup (2007).

Age-related changes in factor VII activation in healthy women

1. To investigate the age-related changes in factor VII activation in healthy women, a regular factor VII clotting assay (factor VIIc) was carried out simultaneously with a new enzyme immunoassay for the quantification of antigen factor VII (factor VIIag). 2. Both factor VIIc and factor VIIag levels were positively correlated with age (r = 0.79 and r = 0.62, respectively, n = 25, P < 0.001). The rise with age in factor VIIc was steeper than in factor VIlag and the ratio of factor VIIc to factor VIlag (an indicator of the activity state of factor VII) increased with age (r = 0.42, P < 0.05). 3. The results show that an increased conversion of native single-chain factor VII to the fully active double-chain form is associated with advancing age in women. 4. This finding is consistent with a possible role of activated factor VII in the pathogenesis of thromboocclusive vascular disease in women.