95 research outputs found
Possible experiment for determination of the role of microscopic vortex rings in the \lambda-transition in He-II
It is suggested that microscopic vortex rings (MVR) play an important role in
the \lambda-transition in helium-II and substantially determine the value of
T_{\lambda}. For very thin films of He-II, with thickness d less than the size
of the smallest MVR, the rings do not fit in and, therefore, do not exist in
such films. Consequently, for superfluid films of He-II, a peculiarity in the
form of a smoothed-out jump should be observed in the curve T_{m}(d) at the
values of thickness approximately equal to the size of the smallest MVR, d= 3 -
9 A (T_{m} is the temperature of the maximum of the broad peak on the curve of
the dependence of the specific heat on temperature). The absence of a similar
peculiarity will be an evidence that MVR do not influence the values of
T_{\lambda} and T_{m}, and do not play any key role in the \lambda-transition.
The currently available experimental data are insufficient for revealing the
predicted peculiarity.Comment: 6 pages, 2 figure
Bose-Einstein condensation in multilayers
The critical BEC temperature of a non interacting boson gas in a
layered structure like those of cuprate superconductors is shown to have a
minimum , at a characteristic separation between planes . It is
shown that for , increases monotonically back up to the ideal
Bose gas suggesting that a reduction in the separation between planes,
as happens when one increases the pressure in a cuprate, leads to an increase
in the critical temperature. For finite plane separation and penetrability the
specific heat as a function of temperature shows two novel crests connected by
a ridge in addition to the well-known BEC peak at associated with the
3D behavior of the gas. For completely impenetrable planes the model reduces to
many disconnected infinite slabs for which just one hump survives becoming a
peak only when the slab widths are infinite.Comment: Four pages, four figure
Local Dynamics and Strong Correlation Physics I: 1D and 2D Half-filled Hubbard Models
We report on a non-perturbative approach to the 1D and 2D Hubbard models that
is capable of recovering both strong and weak-coupling limits. We first show
that even when the on-site Coulomb repulsion, U, is much smaller than the
bandwith, the Mott-Hubbard gap never closes at half-filling in both 1D and 2D.
Consequently, the Hubbard model at half-filling is always in the
strong-coupling non-perturbative regime. For both large and small U, we find
that the population of nearest-neighbour singlet states approaches a value of
order unity as as would be expected for antiferromagnetic order. We
also find that the double occupancy is a smooth monotonic function of U and
approaches the anticipated non-interacting limit and large U limits. Finally,
in our results for the heat capacity in 1D differ by no more than 1% from the
Bethe ansatz predictions. In addition, we find that in 2D, the heat capacity vs
T for different values of U exhibits a universal crossing point at two
characteristic temperatures as is seen experimentally in a wide range of
strongly-correlated systems such as , , and . The
success of this method in recovering well-established results that stem
fundamentally from the Coulomb interaction suggests that local dynamics are at
the heart of the physics of strongly correlated systems.Comment: 10 pages, 16 figures included in text, Final version for publication
with a reference added and minor corrections. Phys. Rev. B, in pres
Associations of common breast cancer susceptibility alleles with risk of breast cancer subtypes in BRCA1 and BRCA2 mutation carriers
Introduction: More than 70 common alleles are known to be involved in breast cancer (BC) susceptibility, and several exhibit significant heterogeneity in their associations with different BC subtypes. Although there are differences in the association patterns between BRCA1 and BRCA2 mutation carriers and the general population for several loci, no study has comprehensively evaluated the associations of all known BC susceptibility alleles with risk of BC subtypes in BRCA1 and BRCA2 carriers. Methods: We used data from 15,252 BRCA1 and 8,211 BRCA2 carriers to analyze the associations between approximately 200,000 genetic variants on the iCOGS array and risk of BC subtypes defined by estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2) and triple-negative- (TN) status; morphologic subtypes; histological grade; and nodal involvement. Results: The estimated BC hazard ratios (HRs) for the 74 known BC alleles in BRCA1 carriers exhibited moderate correlations with the corresponding odds ratios from the general population. However, their associations with ER-positive BC in BRCA1 carriers were more consistent with the ER-positive as
Genome-Wide Association Study in BRCA1 Mutation Carriers Identifies Novel Loci Associated with Breast and Ovarian Cancer Risk
BRCA1-associated breast and ovarian cancer risks can be modified by common genetic variants. To identify further cancer risk-modifying loci, we performed a multi-stage GWAS of 11,705 BRCA1 carriers (of whom 5,920 were diagnosed with breast and 1,839 were diagnosed with ovarian cancer), with a further replication in an additional sample of 2,646 BRCA1 carriers. We identified a novel breast cancer risk modifier locus at 1q32 for BRCA1 carriers (rs2290854, P = 2.7×10-8, HR = 1.14, 95% CI: 1.09-1.20). In addition, we identified two novel ovarian cancer risk modifier loci: 17q21.31 (rs17631303, P = 1.4×10-8, HR = 1.27, 95% CI: 1.17-1.38) and 4q32.3 (rs4691139, P = 3.4×10-8, HR = 1.20, 95% CI: 1.17-1.38). The 4q32.3 locus was not associated with ovarian cancer risk in the general population or BRCA2 carriers, suggesting a BRCA1-specific associat
The Influence of Number and Timing of Pregnancies on Breast Cancer Risk for Women With BRCA1 or BRCA2 Mutations
Background: Full-term pregnancy (FTP) is associated with a reduced breast cancer (BC) risk over time, but women are at
increased BC risk in the immediate years following an FTP. No large prospective studies, however, have examined whether
the number and timing of pregnancies are associated with BC risk for BRCA1 and BRCA2 mutation carriers.
Methods: Using weighted and time-varying Cox proportional hazards models, we investigated whether reproductive events
are associated with BC risk for mutation carriers using a retrospective cohort (5707 BRCA1 and 3525 BRCA2 mutation carriers)
and a prospective cohort (2276 BRCA1 and 1610 BRCA2 mutation carriers), separately for each cohort and the combined prospective and retrospective cohort.
Results: For BRCA1 mutation carriers, there was no overall association with parity compared with nulliparity (combined
hazard ratio [HRc] ¼ 0.99, 95% confidence interval [CI] ¼ 0.83 to 1.18). Relative to being uniparous, an increased number of FTPs was associated with decreased BC risk (HRc¼ 0.79, 95% CI ¼ 0.69 to 0.91; HRc¼ 0.70, 95% CI ¼ 0.59 to 0.82; HRc¼ 0.50, 95%
CI ¼ 0.40 to 0.63, for 2, 3, and 4 FTPs, respectively, Ptrend < .0001) and increasing duration of breastfeeding was associated
with decreased BC risk (combined cohort Ptrend ¼ .0003). Relative to being nulliparous, uniparous BRCA1 mutation carriers
were at increased BC risk in the prospective analysis (prospective hazard ration [HRp] ¼ 1.69, 95% CI ¼ 1.09 to 2.62). For BRCA2
mutation carriers, being parous was associated with a 30% increase in BC risk (HRc ¼ 1.33, 95% CI ¼ 1.05 to 1.69), and there
was no apparent decrease in risk associated with multiparity except for having at least 4 FTPs vs. 1 FTP (HRc¼ 0.72, 95%
CI ¼ 0.54 to 0.98).
Conclusions: These findings suggest differential associations with parity between BRCA1 and BRCA2 mutation carriers with
higher risk for uniparous BRCA1 carriers and parous BRCA2 carriers
The TAIH-C measures of attention
The Test of Attention Impulsivity and Hyperactivity in Children (TAIH-C) measures auditory and visual attention independently. The measures are based on a multifactorial model of attention, incorporating General Alertness, Sustained Attention Vigilance, Selective Attention and Divided Attention. They are designed to be free of academic knowledge; culture, gender and age bias. Practice effects are minimal and the attention tasks increase incrementally in difficulty. The two attention scales of the TAIH-C are designed to discriminate between children ranging in age from 6-16 years. In this paper, the performance on both attention scales of children independently diagnosed with ADHD is compared to that of non-ADHD peers
The assessment and diagnosis of Attention Deficit Hyperactivity Disorder (ADHD) in children
We examine the current definition of ADHD and its subtypes and the diagnostic procedure described in the DSM-IV. The use of parent and teacher reports and behaviour rating scales in the diagnostic process is also evaluated. The value of more objective data sources, such as direct observations, simulated environments, and continuous performance tests is highlighted. We also describe the measurement of the three behavioural domains of ADHD – Inattention, Hyperactivity and Impulsivity – according to current theory and research. We suggest that greater attention to this literature will help the development of comprehensive, standardised performance tests that add precision to the assessment and diagnosis of ADHD and the ADHD construct itself
The validation and utility of the Test of Attention Impulsivity and Hyperactivity in Children (TAIH-C)
ADHD remains controversial in both its diagnosis and its treatment. Currently, diagnosis and assessment of ADHD rely on the use of questionnaires, rating scales, evaluation based on DSM-IV criteria, and continuous performance tests, all of which have their own weaknesses. This paper reports on the development of the Test of Attention Impulsivity and Hyperactivity in Children (TAIH-C), a standardised, behaviour based assessment of attention impulsivity and hyperactivity in children with ADHD. We present individual and group data on children independently diagnosed with ADHD and nonADHD classroom peers, to validate the implementation of the TAIH-C as a valuable tool in both diagnosing ADHD and designing precise
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