On SAT representations of XOR constraints

We study the representation of systems S of linear equations over the two-element field (aka xor- or parity-constraints) via conjunctive normal forms F (boolean clause-sets). First we consider the problem of finding an "arc-consistent" representation ("AC"), meaning that unit-clause propagation will fix all forced assignments for all possible instantiations of the xor-variables. Our main negative result is that there is no polysize AC-representation in general. On the positive side we show that finding such an AC-representation is fixed-parameter tractable (fpt) in the number of equations. Then we turn to a stronger criterion of representation, namely propagation completeness ("PC") --- while AC only covers the variables of S, now all the variables in F (the variables in S plus auxiliary variables) are considered for PC. We show that the standard translation actually yields a PC representation for one equation, but fails so for two equations (in fact arbitrarily badly). We show that with a more intelligent translation we can also easily compute a translation to PC for two equations. We conjecture that computing a representation in PC is fpt in the number of equations.Comment: 39 pages; 2nd v. improved handling of acyclic systems, free-standing proof of the transformation from AC-representations to monotone circuits, improved wording and literature review; 3rd v. updated literature, strengthened treatment of monotonisation, improved discussions; 4th v. update of literature, discussions and formulations, more details and examples; conference v. to appear LATA 201

The Mechanism of Electro-Reduction of Chromate in Molten LiCl-KCl

When chromate ion is electro-reduced in molten LiCl- KCl in the presence of Mg (II), Zn (II) or Ni (II), the product is typically of composition LixMyCr04 , in which X + 2 Y = 5. Variations in composition accompany variations is experimental conditions, except in the case of Zn(II), for which X = 1 and Y = · 2. With Co (II), the product is either LixCoyCr04 or Co2Cr04 or a mixture of the two, depending upon the conditions. A mechanism involving a first two-electron reduction followed by a competition between further one-electron reduction and an internal chemical redox reaction accounts -satisfactorily for the variation of product with changes in experimental conditions

Kaivosteollisuuden raskasmetallipäästöjen vaikutukset kasveihin

Tiivistelmä. Tutkielmassa avataan biologisen raskasmetallikäsitteen määritelmää, sekä luodaan yleiskatsaus raskasmetallipäästöistä kasveille aiheutuviin haittoihin, painottuen erityisesti kaivostoimintaan ja siihen sidoksissa olevaan raskaaseen teollisuuteen. Tarkastelun kohteena ovat raskasmetallien yhteiset piirteet sekä eräät yleisluontoiset seikat, jotka vaikuttavat niiden toimintaan, kuten maaperän happamuus ja luonnossa esiintyvät saman metallin erilaiset esiintymismuodot. Lisäksi verrataan metallien erilaisia tapoja päätyä sisälle kasviyksilöön, kulkeutua kasvin eri osiin sekä varastoitua ja vaikuttaa kasvin elintoimintoihin, erityisesti happiradikaaleja synnyttävien reaktioiden alullepanijoina ja stimuloijina, sekä fotosynteesin reaktioiden redusoijina. Yleisimpien kaivosteollisuudessa esiintyvien metallien biologisesti toiminnalliset erityispiirteet käydään läpi ja huomioidaan niiden keskinäiset erot sekä kasveille välttämättöminä että haitallisina tekijöinä. Todetaan, että metallien myrkyllisyys pieninäkin pitoisuuksina ei suoraan tee niistä merkittävimpiä saastumisongelmien aiheuttajia, vaan kasveille elintärkeät metallit saattavat suuremman esiintyneisyytensä vuoksi aiheuttaa kasveille kokonaisuudessaan kattavampia ongelmia. Työssä tarkastellaan kaivosteollisuuden menetelmiä yleisluontoisesti käyttäen esimerkkinä kahden Suomessa eniten jalostettavan metallin työstövaiheet kallioperästä raakametalleiksi. Prosessien potentiaalisia valuvikoja voidaan arvioida havainnoitaessa päästöjen aiheuttamia ongelmia ja ympäristön puhdistuksen haasteita erityisesti kehittyvien maiden näkökulmasta. Käydään läpi saastuneen alueen ekologiseen restoraatioon liittyviä menetelmiä ja niiden rajoitteita. Lisäksi sivutaan hieman metallipäästöjen vaikutuksia biodiversiteetin tasoihin suhteutettuna. Kasvien fytoremediaatiokyvyn taustalla olevia evoluution valintapaineita eritellään, ja käydään läpi fytoremediaatiokykyisten taksonien eroja ja fytoremediaatiomuotojen käyttökelpoisuutta toimivien restoraatiostrategioiden kehittämisen kannalta. Todetaan fytoremediaatiokyvyn olevan kasvikunnassa harvinainen sekä rajoitteinen esimerkiksi siten, että yhden kasvin kyky kumuloida erilaisia metalleja itseensä on rajoittunut, sekä metallien kumuloimisprosessin olevan siihen kykenevällekin kasville tuntuva stressitekijä, joka saattaa rajoittaa esimerkiksi sen biomassan tuottoa. Lopuksi sivutaan lyhyesti geeninsiirtotekniikalla luotujen metalleja hyperakkumuloivien kasvien mahdollisuuksia ja riskejä, sekä teollistuneiden ja kehittyvien maiden epätasa-arvoisia mahdollisuuksia ekologisten restoraatiotoimenpiteiden suunnittelussa ja toteutuksessa

Solar interacting protons versus interplanetary protons in the core plus halo model of diffusive shock acceleration and stochastic re-acceleration

With the first observations of solar γ-rays from the decay of pions, the relationship of protons producing ground level enhancements (GLEs) on the Earth to those of similar energies producing the γ-rays on the Sun has been debated. These two populations may be either independent and simply coincident in large flares, or they may be, in fact, the same population stemming from a single accelerating agent and jointly distributed at the Sun and also in space. Assuming the latter, we model a scenario in which particles are accelerated near the Sun in a shock wave with a fraction transported back to the solar surface to radiate, while the remainder is detected at Earth in the form of a GLE. Interplanetary ions versus ions interacting at the Sun are studied for a spherical shock wave propagating in a radial magnetic field through a highly turbulent radial ray (the acceleration core) and surrounding weakly turbulent sector in which the accelerated particles can propagate toward or away from the Sun. The model presented here accounts for both the first-order Fermi acceleration at the shock front and the second-order, stochastic re-acceleration by the turbulence enhanced behind the shock. We find that the re-acceleration is important in generating the γ-radiation and we also find that up to 10% of the particle population can find its way to the Sun as compared to particles escaping to the interplanetary space

Locally recurrent chondrosarcoma of the pelvis and limbs can only be controlled by wide local excision

Aims The purpose of this study was to investigate the potential for achieving local and systemic control after local recurrence of a chondrosarcoma of bone. Patients and Methods A total of 126 patients with local recurrence (LR) of chondrosarcoma (CS) of the pelvis or a limb bone were identified from a prospectively maintained database, between 1990 and 2015 at the Royal Orthopaedic Hospital, Birmingham, United Kingdom. There were 44 female patients (35%) and 82 male patients (65%) with a mean age at the time of LR of 56 years (13 to 96). The 126 patients represented 24.3% of the total number of patients with a primary CS (519) who had been treated during this period. Clinical data collected at the time of primary tumour and LR included the site (appendicular, extremity, or pelvis); primary and LR tumour size (in centimetres); type of operation at the time of primary or LR (limb-salvage or amputation); surgical margin achieved at resection of the primary tumour and the LR; grade of the primary tumour and the LR; gender; age; and oncological outcomes, including local recurrence-free survival and disease-specific survival. A minimum two years' follow-up and complete histopathology records were available for all patients included in the study. Results For patients without metastases prior to or at the time of local recurrence, the disease-specific survival after local recurrence was 62.5% and 45.5% at one and five years, respectively, After univariable analysis, significant factors predicting disease-specific survival were grade (p <0.001) and surgical margin (p = 0.044). After multivariable analysis, grade, increasing age at the time of diagnosis of local recurrence, and a greater time interval from primary surgery to local recurrence were significant factors for disease-specific survival. A secondary local recurrence was seen in 26% of patients. Wide margins were a good predictor of local recurrence-free survival for subsequent recurrences after univariable analysis when compared with intralesional margins (p = 0.002) but marginal margins did not reach statistical significance when compared with intralesional margins (p = 0.084). Conclusion In cases of local recurrence of a chondrosarcoma of bone, we have shown that if the tumour is non-metastatic at re-staging, an increase in disease-specific survival and in local recurrence-free survival is achievable, but only by resection of the local recurrence with a wide margin.Peer reviewe

Factors associated with parental recognition of a child's overweight status - a cross sectional study

<p>Abstract</p> <p>Background</p> <p>Very few studies have evaluated the association between a child's lifestyle factors and their parent's ability to recognise the overweight status of their offspring. The aim of this study was to analyze the factors associated with a parent's ability to recognise their own offspring's overweight status.</p> <p>Methods</p> <p>125 overweight children out of all 1,278 school beginners in Northern Finland were enrolled.</p> <p>Weight and height were measured in health care clinics. Overweight status was defined by BMI according to internationally accepted criteria. A questionnaire to be filled in by parents was delivered by the school nurses. The parents were asked to evaluate their offspring's weight status. The child's eating habits and physical activity patterns were also enquired about. Factor groups of food and physical activity habits were formed by factor analysis. Binary logistic regression was performed using all variables associated with recognition of overweight status in univariate analyses. The significant risk factors in the final model are reported using odds ratios (ORs) and their 95% confidence intervals (CIs).</p> <p>Results</p> <p>Fifty-seven percent (69/120) of the parents of the overweight children considered their child as normal weight. Child's BMI was positively associated with parental recognition of overweight (OR 3.59, CI 1.8 to 7.0). Overweight boys were less likely to be recognised than overweight girls (OR 0.14, CI 0.033 to 0.58). Child's healthy diet (OR 0.22, CI 0.091 to 0.54) and high physical activity (OR 0.29, CI 0.11 to 0.79) were inversely related to parental recognition of overweight status.</p> <p>Conclusions</p> <p>Child's healthy eating habits and physical activity are inversely related to parental recognition of their offspring's overweight. These should be taken into account when planning prevention and treatment strategies for childhood obesity.</p

From Sun to Interplanetary Space: What is the Pathlength of Solar Energetic Particles?

Solar energetic particles (SEPs), accelerated during solar eruptions, propagate in turbulent solar wind before being observed with in situ instruments. In order to interpret their origin through comparison with remote sensing observations of the solar eruption, we thus must deconvolve the transport effects due to the turbulent magnetic fields from the SEP observations. Recent research suggests that the SEP propagation is guided by the turbulent meandering of the magnetic fieldlines across the mean magnetic field. However, the lengthening of the distance the SEPs travel, due to the fieldline meandering, has so far not been included in SEP event analysis. This omission can cause significant errors in estimation of the release times of SEPs at the Sun. We investigate the distance traveled by the SEPs by considering them to propagate along fieldlines that meander around closed magnetic islands that are inherent in turbulent plasma. We introduce a fieldline random walk model which takes into account the physical scales associated to the magnetic islands. Our method remedies the problem of the diffusion equation resulting in unrealistically short pathlengths, and the fractal dependence of the pathlength of random walk on the length of the random-walk step. We find that the pathlength from the Sun to 1au can be below the nominal Parker spiral length for SEP events taking place at solar longitudes 45E to 60W, whereas the western and behind-the-limb particles can experience pathlengths longer than 2au due to fieldline meandering