Cooperative DNA-binding by Bicoid provides a mechanism for threshold-dependent gene activation in the Drosophila embryo

The Bicoid morphogen directs pattern formation along the anterior-posterior (A-P) axis of the Drosophila embryo. Bicoid is distributed in a concentration gradient that decreases exponentially from the anterior pole, however, it transcribes target genes such as hunchback in a step-function-like pattern; the expression domain is uniform and has a sharply defined posterior boundary. A 'gradient-affinity' model proposed to explain Bicoid action states that (i) cooperative gene activation by Bicoid generates the sharp on/off switch for target gene transcription and (ii) target genes with different affinities for Bicoid are expressed at different positions along the A-P axis. Using an in vivo yeast assay and in vitro methods, we show that Bicoid binds DNA with pairwise cooperativity; Bicoid bound to a strong site helps Bicoid bind to a weak site. These results support the first aspect of the model, providing a mechanism by which Bicoid generates sharp boundaries of gene expression. However, contrary to the second aspect of the model, we find no significant difference between the affinity of Bicoid for the anterior gene hunchback and the posterior gene knirps, We propose, instead, that the arrangement of Bicoids bound to the target gene presents a unique signature to the transcription machinery that, in combination with overall affinity, regulates the extent of gene transcription along the A-P axis

Investigating the pre-main sequence magnetic chemically peculiar system HD 72106

The origin of the strong magnetic fields observed in chemically peculiar Ap and Bp stars stars has long been debated. The recent discovery of magnetic fields in the intermediate mass pre-main sequence Herbig Ae and Be stars links them to Ap and Bp stars, providing vital clues about Ap and Bp stars and the origin and evolution of magnetic fields in intermediate and high mass stars. A detailed study of one young magnetic B star, HD 72106A, is presented. This star appears to be in a binary system with an apparently normal Herbig Ae star. A maximum longitudinal magnetic field strength of +391 +/- 65 G is found in HD 72106A, as are strong chemical peculiarities, with photospheric abundances of some elements ranging up to 100x above solar.Comment: 8 pages, 6 figures. Proceeding of the 2006 conference of the Special Astrophysical Observatory of the Russian Academy of Science

Critical evaluation of magnetic field detections reported for pulsating B-type stars in the light of ESPaDOnS, Narval and reanalyzed FORS1/2 observations

Recent spectropolarimetric studies of 7 SPB and $\beta$ Cep stars have suggested that photospheric magnetic fields are more common in B-type pulsators than in the general population of B stars, suggesting a significant connection between magnetic and pulsational phenomena. We present an analysis of new and previously published spectropolarimetric observations of these stars. New Stokes $V$ observations obtained with the high-resolution ESPaDOnS and Narval instruments confirm the presence of a magnetic field in one of the stars ($\epsilon$ Lup), but find no evidence of magnetism in 5 others. A re-analysis of the published longitudinal field measurements obtained with the low-resolution FORS1/2 spectropolarimeters finds that the measurements of all stars show more scatter from zero than can be attributed to Gaussian noise, suggesting the presence of a signal and/or systematic under-estimation of error bars. Re-reduction and re-measurement of the FORS1/2 spectra from the ESO archive demonstrates that small changes in reduction procedure lead to substantial changes in the inferred longitudinal field, and substantially reduces the number of field detections at the 3$\sigma$ level. Furthermore, we find that the published periods are not unique solutions to the time series of either the original or the revised FORS1/2 data. We conclude that the reported field detections, proposed periods and field geometry models for $\alpha$ Pyx, 15 CMa, 33 Eri and V1449 Aql are artefacts of the data analysis and reduction procedures, and that magnetic fields at the reported strength are no more common in SPB/$\beta$ Cep stars than in the general population of B stars.Comment: 10 pages, 5 figures, accepted for publication in ApJ, 2012, typo correcte

Major hepatic resections – the progress of a new HBP surgical-centre

Spitalul Clinic “Dr. Ion Cantacuzino”, București, România, Al XIII-lea Congres al Asociației Chirurgilor „Nicolae Anestiadi” și al III-lea Congres al Societății de Endoscopie, Chirurgie miniminvazivă și Ultrasonografie ”V.M.Guțu” din Republica MoldovaIntroducere: In mod istoric, rezecțiile hepatice au fost insoțite de morbitate si morbitate majore, reprezentând un tip prohibitiv de chirurgie până în ultimii ani. Odata cu evoluția tehnologiei și imbunătățirea tehnicilor imagistice, cât și a dezvoltării unui management perioperator specific ficatului, rezectiile hepatice au ajuns sa fie efectuate în centre de volum mare cu o rată a mortalitații de < 5%. Material si metode: În ultimii 5 ani, Spitalul Clinic “Dr. Ion Cantacuzino” s-a dezvoltat ca un nou centru de chirurgie hepato-biliopancreatică, o varietate largă de rezecții hepatice fiind practicate de rutină. Rezultate: Experiența acestei clinici în ceea ce privește rezecțiile hepatice majore a progresat până la 15 cazuri, la ora actuală, cu un singur deces postoperator. Concluzii: Din perspectiva unui centru în creștere a devenit aparent faptul ca se pot realiza rezecții hepatice majore în siguranță și cu rezultate postoperatorii bune, atât timp cât se aplica o selecție riguroasă a pacienților și sunt urmarite protocoale standardizate.Background: Historically major hepatic resections have been associated with high morbidity and mortality, being a prohibitive type surgery until recent years. With the advancement of technology and better imaging techniques, as well as liver-specific perioperative care, hepatic resections are performed in high-volume centres with a mortality of less than 5 %. Method and materials: The “Dr. Ion Cantacuzino” Hospital in Bucharest has developed as a new hepato-biliary-pancreatic surgical centre in the past 5 years, with a wide variety of hepatic resections performed on a regular basis. Results: The experience of this clinic, as far as major hepatic resections is concerned, has progressed, to date, to 15 such cases, with just one postoperative death. Conclusion: From the perspective of a growing centre it has become apparent that major hepatic resections can be safely performed and with good postoperative outcomes, with a thorough selection of patients and if standardised protocols are followed

Colloids in light fields: particle dynamics in random and periodic energy landscapes

The dynamics of colloidal particles in potential energy landscapes have mainly been investigated theoretically. In contrast, here we discuss the experimental realization of potential energy landscapes with the help of light fields and the observation of the particle dynamics by video microscopy. The experimentally observed dynamics in periodic and random potentials are compared to simulation and theoretical results in terms of, e.g. the mean-squared displacement, the time-dependent diffusion coefficient or the non-Gaussian parameter. The dynamics are initially diffusive followed by intermediate subdiffusive behaviour which again becomes diffusive at long times. How pronounced and extended the different regimes are, depends on the specific conditions, in particular the shape of the potential as well as its roughness or amplitude but also the particle concentration. Here we focus on dilute systems, but the dynamics of interacting systems in external potentials, and thus the interplay between particle-particle and particle-potential interactions, is also mentioned briefly. Furthermore, the observed dynamics of dilute systems resemble the dynamics of concentrated systems close to their glass transition, with which it is compared. The effect of certain potential energy landscapes on the dynamics of individual particles appears similar to the effect of interparticle interactions in the absence of an external potential

Globular Cluster Systems in Brightest Cluster Galaxies: Bimodal Metallicity Distributions and the Nature of the High-Luminosity Clusters

We present new (B,I) photometry for the globular cluster systems in eight Brightest Cluster Galaxies (BCGs), obtained with the ACS/WFC camera on the Hubble Space Telescope. In the very rich cluster systems that reside within these giant galaxies, we find that all have strongly bimodal color distributions All the BCGs show population gradients, with much higher relative numbers of red clusters within 5 kpc of their centers, consistent with their having formed at later times than the blue, metal-poor population. A striking new feature of the color distributions emerging from our data is that for the brightest clusters (M_I < -10.5) the color distribution becomes broad and less obviously bimodal. we suggest that it may be a characteristic of many BCGs. Furthermore, the blue (metal-poor) clusters become progressively redder with increasing luminosity, following a mass/metallicity scaling relation Z ~ M^0.55. We argue that these GCS characteristics are consistent with a hierarchical-merging formation picture in which the metal-poor clusters formed in protogalactic clouds or dense starburst complexes with gas masses in the range 10^7 - 10^10 M_Sun, but where the more massive clusters on average formed in bigger clouds with deeper potential wells where more pre-enrichment could occur.Comment: 48 pages, 24 Figures, PDF, Submitted to Astrophys.J. and refereed. For complete pdf file with better figures, see: http://physwww.mcmaster.ca/%7Eharris/Preprints.htm

hernia repair – is there a place for one-day surgery?

Spitalul Clinic “Dr. Ion Cantacuzino”, București, România, Al XIII-lea Congres al Asociației Chirurgilor „Nicolae Anestiadi” și al III-lea Congres al Societății de Endoscopie, Chirurgie miniminvazivă și Ultrasonografie ”V.M.Guțu” din Republica MoldovaIntroducere: Tratamentul chirurgical al herniilor inghinale este una dintre cele mai frecvente intervenții chirurgicale care se practică pe plan mondial, în ciuda faptului că persistă o lipsă de conses în ceea ce privește “cel mai bun” procedeu; unii autori susținând avantajele procedeelor deschise, în principiu operația Lichtenstein, în timp ce alții beneficiile abordarilor laparoscopice, TAPP sau TEP. Material și metode: Am realizat un studiu retrospectiv în cadrul Spitalului Clinic “Dr. Ion Cantacuzino”, pe o perioadă de 5 ani, pe 517 pacienți la care s-au practicat diferite intervenții chirurgicale pentru tratamentul herniilor inghinale. Pacienții au fost imparțiți în 2 grupuri, unii beneficiind de un procedeu deschis, în timp ce alții de laparoscopie. Variabile introduse în studiu au fost vârsta, sexul, perioada medie de spitalizare, media zilelor de spitalizare postoperatorie, timpul operatorie si costurile aferente spitalizării. Rezultate: Procedee laparoscopice s-au efectuat la 304/517 (59,37%), cu o mică prevalență TEP vs TAPP. Perioada de spitalizare, cheltuielile și timpii operatori au fost semnificativ mai mici pentru grupul TEP, majoritatea pacientilor fiind externați în prima zi postoperator. Concluzii: Rezultatele studiului nostru sprijină ideea ca procedeul TEP se poate practica într-un regim de “one-day surgery” într-un spital public astfel crescând confortul pacientului și scazând cheltuielile de spitalizare.Background: Hernia surgery is one of the most frequent operation performed world-wide, although there still seems to be a lack of consensus as to “the best” technique, with some authors still advocating for open, mainly Lichtenstein repair, while others supporting laparoscopic techniques, TAPP or TEP. Methods and materials: A retrospective study was performed in a public county hospital, over a period of 5 years, on 517 patients who benefitted from a surgical procedure for inguinal hernia treatment. Patients were divided into 2 groups, one with open surgical repair and, the other, laparoscopic. Variables taken into account were age, sex, mean hospital stay, mean postoperative hospital stay, hospital expenses, and operative time. Results: Laparoscopic repair was performed for 304/517 (59,37%), with a slight prevalence of TEP over TAPP; Hospital stay, expenses and operative time were significantly lower for the TEP group, most of the patients being discharged the following day. Conclusion: The results of our study seems to support the idea that TEP hernia repair could be performed on a “one-day surgery” basis in a public hospital, thus increasing patient comfort and decreasing hospital expenses