1,094 research outputs found
First-Order Query Evaluation with Cardinality Conditions
We study an extension of first-order logic that allows to express cardinality
conditions in a similar way as SQL's COUNT operator. The corresponding logic
FOC(P) was introduced by Kuske and Schweikardt (LICS'17), who showed that query
evaluation for this logic is fixed-parameter tractable on classes of structures
(or databases) of bounded degree. In the present paper, we first show that the
fixed-parameter tractability of FOC(P) cannot even be generalised to very
simple classes of structures of unbounded degree such as unranked trees or
strings with a linear order relation.
Then we identify a fragment FOC1(P) of FOC(P) which is still sufficiently
strong to express standard applications of SQL's COUNT operator. Our main
result shows that query evaluation for FOC1(P) is fixed-parameter tractable
with almost linear running time on nowhere dense classes of structures. As a
corollary, we also obtain a fixed-parameter tractable algorithm for counting
the number of tuples satisfying a query over nowhere dense classes of
structures
Deciding first-order properties of nowhere dense graphs
Nowhere dense graph classes, introduced by Nesetril and Ossona de Mendez,
form a large variety of classes of "sparse graphs" including the class of
planar graphs, actually all classes with excluded minors, and also bounded
degree graphs and graph classes of bounded expansion.
We show that deciding properties of graphs definable in first-order logic is
fixed-parameter tractable on nowhere dense graph classes. At least for graph
classes closed under taking subgraphs, this result is optimal: it was known
before that for all classes C of graphs closed under taking subgraphs, if
deciding first-order properties of graphs in C is fixed-parameter tractable,
then C must be nowhere dense (under a reasonable complexity theoretic
assumption).
As a by-product, we give an algorithmic construction of sparse neighbourhood
covers for nowhere dense graphs. This extends and improves previous
constructions of neighbourhood covers for graph classes with excluded minors.
At the same time, our construction is considerably simpler than those. Our
proofs are based on a new game-theoretic characterisation of nowhere dense
graphs that allows for a recursive version of locality-based algorithms on
these classes. On the logical side, we prove a "rank-preserving" version of
Gaifman's locality theorem.Comment: 30 page
Staining and peeling of the internal limiting membrane using a fluorescent dye (Rhodamine 6 G)
Aim: To assess whether low concentrations of a fluorescent dye such as Rhodamine 6G would help the unaided human eye visualise the vitreous and the internal limiting membrane (ILM) under standard halogen illumination.Material/methods: The UV/Vis absorption (E) and fluorescence (I) spectra of Rhodamine 6G in water were measured and compared with Indocyanine Green (ICG). Surgery was performed in two rhesus monkeys and consisted of standard pars plana vitrectomy with halogen light source used for illumination. Rhodamine 6G was diluted in balanced salt solution (BSS). A few drops of the dye in a concentration of 0.1% (307 mOsm) were applied over the posterior pole in the air-filled globe and washed out by irrigation after 1 min. Immediately after surgery, the globes were enucleated, fixated and prepared for histological evaluation.Results: In contrast to ICG, both the maximum of the absorption and emission of Rhodamin 6G are very much within the spectral sensitivity of the human eye. The Rhodamine 6G--BSS itself appears red in colour. Using a dye concentration of 0.1%, there was no visible red-staining of the ILM as such. As the dye was irrigated out with BSS, a marked green fluorescence of the fluid within the vitreous cavity was noted. With halogen illumination through a standard 20-gauge light pipe, the dye provided a sufficient green fluorescence to identify and safely remove the ILM and to clearly differentiate areas of peeled from non-peeled ILM. During light microscopy, eyes revealed a peeled ILM demarcation with no signs of acute retinal toxicity.Conclusion: The findings indicate that a fluorescent dye can be used for ILM peeling. Assuming that the fluorophore provides a high enough fluorescence quantum yield after adsorption to the ILM, much lower dye concentrations could be used compared with absorbent dyes, thereby minimising toxic effects
Cotranscription of the electron transport protein genes nifJ and nifF in Enterobacter agglomerans 333
A nucleotide sequence showing extensive homology to the nifF gene, which codes for a flavodoxin involved in nitrogen fixation in Klebsiella pneumoniae, was localized on the plasmid pEA3 of Enterobacter agglomerans and determined. The analysis of transcriptional fusions, as well as transcript protection assays, indicated a novel nif gene organization, that is, the cotranscription of nifJ and nifF
Routing with Congestion in Acyclic Digraphs
We study the version of the -disjoint paths problem where demand pairs
, , are specified in the input and the paths in
the solution are allowed to intersect, but such that no vertex is on more than
paths. We show that on directed acyclic graphs the problem is solvable in
time if we allow congestion for paths. Furthermore, we
show that, under a suitable complexity theoretic assumption, the problem cannot
be solved in time for any computable function
Technical note:On the reliability of laboratory beta-source calibration for luminescence dating
The dose rate of the 90Sr / 90Y beta source used in most
luminescence readers is a laboratory key parameter. There is a
well-established body of knowledge about parameters controlling accuracy and
precision of the calibration value but some hard-to-explain inconsistencies
still exist. Here, we have investigated the impact of grain size, aliquot
size and irradiation geometry on the resulting calibration value through
experiments and simulations. The resulting data indicate that the dose rate
of an individual beta source results from the interplay of a number of
parameters, most of which are well established by previous studies. Our
study provides evidence for the impact of aliquot size on the absorbed dose
in particular for grain sizes of 50–200 µm. For this grain-size
fraction, the absorbed dose is enhanced by ∼ 10 %–20 % as
aliquot size decreases due to the radial increase of dose rate towards
the centre of the aliquot. The enhancement is most variable for 50–100 µm
grains mounted as aliquots of < 8 mm size. The enhancement is
reversed when large grains are mounted as small aliquots due to the edge
effect by which the dose induced by backscattered electrons is reduced.
While the build-up of charge dictates the increase of absorbed dose with the
increase of grain size, this principle becomes more variable with changing
irradiation geometry. We conclude that future calibration samples should
consist of subsamples composed of small, medium, large and very large quartz
grains, each obtaining several gamma doses. The calibration value measured
with small, medium and large aliquots is then obtained from the inverse
slope of the fitted line, not from a single data point. In this way, all
possible irradiation geometries of an individual beta source are covered,
and the precision of the calibration is improved.</p
Les sables de Fontainebleau: a natural quartz reference sample and its characterisation
Fundamental studies on luminescence production
in natural quartz require samples
which can be studied by groups of laboratories
using complementary methods. In the framework
of a European collaboration studying
quartz luminescence, a sample originating
from the Fontainebleau Sandstone Formation
in France was selected for characterisation
and distribution to establish a starting point
for interlaboratory work. Here we report on
the preparation and characterisation work
undertaken before distribution with the aim
of ensuring that each laboratory received
comparable material. Material was purified to
enrich the quartz concentration, followed by
mineralogical screening by SEM and ICP-MS
analyses. Luminescence screening measurements
were undertaken at a single laboratory
(SUERC) to verify the suitability of the sample
for use within the study, and to establish the
level of homogeneity of subsamples prepared
for distribution. The sample underwent minimal
non-chemical pre-treatment by multiple
cycles of magnetic separation and annealing.
SEM analysis showed that the sample
consists mainly of SiO2. The luminescence
characterisation confirmed a dose sensitivity
of ca. 22,000–160,000 cts K−1 Gy−1 per 260–
290 grains for the 110◦C UV TL peak, well
developed low (here: 100–300◦C) temperature
(pre-dose) TL signals and high OSL sensitivities.
The grain to grain OSL response varies by
more than one order of magnitude. No significant
IRSL signal was observed. In summary,
the results from luminescence characterisation
confirm the suitability of the sample for the
luminescence experiments envisaged and have
established a basis for comparability in studies
conducted by a network of laboratories
Intravitreal bevacizumab for the treatment of macular oedema secondary to branch retinal vein occlusion
Purpose: To evaluate the effect of intravitreal bevacizumab (Avastin) injections on visual acuity (VA) and foveal retinal thickness in patients with macular oedema secondary to branch retinal vein occlusion.Methods: A prospective, non-comparative, consecutive, interventional case series of 34 patients. Patients received repeated intravitreal injections of 1.25 mg bevacizumab. Main outcome measures were VA (Snellen charts and ETDRS) and retinal thickness (optical coherence tomography measurements) in a follow-up period of 6 months.Results: Patients presented at a mean age of 69 years (range 44--86). Mean duration of symptoms was 40 weeks (range 1--300). Mean (SD) VA at baseline was 0.79 (0.39) logMAR, improving to 0.51 (0.34) logMAR at 6 months (p = 0.009). Mean number of letters on the ETDRS chart at baseline was 45.3 (19.0), improving to 60.6 (19.9) at 6 months (p = 0.003). Mean (SD) retinal thickness at baseline was 474 (120) \textgreekmm, declining to 316 (41) \textgreekmm at 6 months.Conclusion: Intravitreal injection of 1.25 mg bevacizumb appears to be an effective treatment option for branch retinal vein occlusion
Decal: indirect transfer printing technique and its advanced applications in contemporary ceramic art
Transfer baskı, farklı yüzeylere uygulanabilmesi nedeniyle sanatsal ifadelerde yaratıcı fikirler üretilmesine olanak sağlayan, oldukça heyecan verici bir yöntemdir. Bu yöntem çeşitti uygulama teknikleriyle seramik alanında da yaygın olarak kullanılmaktadır. Seramikte uygulanan transfer baskı tekniklerinden biri de, 'indirekt transfer tekniği' olarak anılan 'çıkartma' /a da bir diğer adıyla 'dekal'dır. Seramik endüstrisinin yanı sıra çağdaş seramik sanatında da kullanılan çıkartma, bir dekor tekniği olarak, düz olmayan yüzeye uygulanabilir olması nedeniyle tercih edilmektedir. Çıkartma, sağlık koşulları açısından zararsız su bazlı malzemelerin geliştirilmesi ve bilgisayar destekli dijital uygulamaların bu alana uyarlanması ile günümüzde çok farklı şekillerde kullanılmaktadır. Bu makalede, çıkartma tekniğinin tarih içinde gelişimi, günümüz seramik sanatçılarının bu alanda yaptıkları araştırmalar ve günümüzde geliştirdikleri yeni tekniklere yer verdikleri çalışmalarının uygulama aşamaları incelenmekte ve aralarındaki uygulama farklılıkları açıklanmaktadır. Tranfer printing, which enables artists to produce creative ideas, is quite exciting method as it can be applied on various surfaces. With diverse range of its application techniques, this method is widely used in the field of ceramics. One of the tranfer printing techniques that is applied on ceramics is the water slide transfer which is called "indirect transfer technique", or in other words "decal". The water slide transfer technique, which is used in ceramic industry and in contemporary ceramic art as welt, is preferred because it is applicable on uneven surfaces. Today, water slide transfer technique is applied in a variety of different ways by means of wholesome and advanced water-based materials, and with the help of adapting digital sources to this field. This paper examines the development of water slide transfer technique throughout its history; the advanced techniques and researches conducted by contemporary ceramic artists and intends to explain the phases of their diverse practices. 
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