Smectic ordering in liquid crystal - aerosil dispersions I. X-ray scattering

Comprehensive x-ray scattering studies have characterized the smectic ordering of octylcyanobiphenyl (8CB) confined in the hydrogen-bonded silica gels formed by aerosil dispersions. For all densities of aerosil and all measurement temperatures, the correlations remain short range, demonstrating that the disorder imposed by the gels destroys the nematic (N) to smectic-A (SmA) transition. The smectic correlation function contains two distinct contributions. The first has a form identical to that describing the critical thermal fluctuations in pure 8CB near the N-SmA transition, and this term displays a temperature dependence at high temperatures similar to that of the pure liquid crystal. The second term, which is negligible at high temperatures but dominates at low temperatures, has a shape given by the thermal term squared and describes the static fluctuations due to random fields induced by confinement in the gel. The correlation lengths appearing in the thermal and disorder terms are the same and show strong variation with gel density at low temperatures. The temperature dependence of the amplitude of the static fluctuations further suggests that nematic susceptibility become suppressed with increasing quenched disorder. The results overall are well described by a mapping of the liquid crystal-aerosil system into a three dimensional XY model in a random field with disorder strength varying linearly with the aerosil density.Comment: 14 pages, 13 figure

Hydrogen-bonded Silica Gels Dispersed in a Smectic Liquid Crystal: A Random Field XY System

The effect on the nematic to smectic-A transition in octylcyanobiphenyl (8CB) due to dispersions of hydrogen-bonded silica (aerosil) particles is characterized with high-resolution x-ray scattering. The particles form weak gels in 8CB creating a quenched disorder that replaces the transition with the growth of short range smectic correlations. The correlations include thermal critical fluctuations that dominate at high temperatures and a second contribution that quantitatively matches the static fluctuations of a random field system and becomes important at low temperatures.Comment: 10 pages, 4 postscript figures as separate file

The order of the metal to superconductor transition

We present results from large-scale Monte Carlo simulations on the full Ginzburg-Landau (GL) model, including fluctuations in the amplitude and the phase of the matter-field, as well as fluctuations of the non-compact gauge-field of the theory. {}From this we obtain a precise critical value of the GL parameter \kct separating a first order metal to superconductor transition from a second order one, \kct = (0.76\pm 0.04)/\sqrt{2}. This agrees surprisingly well with earlier analytical results based on a disorder theory of the superconductor to metal transition, where the value \kct=0.798/\sqrt{2} was obtained. To achieve this, we have done careful infinite volume and continuum limit extrapolations. In addition we offer a novel interpretation of \kct, namely that it is also the value separating \typeI and \typeII behaviour.<Comment: Minor corrections, present version accepted for publication in PR

The finite-temperature chiral transition in QCD with adjoint fermions

We study the nature of the finite-temperature chiral transition in QCD with N_f light quarks in the adjoint representation (aQCD). Renormalization-group arguments show that the transition can be continuous if a stable fixed point exists in the renormalization-group flow of the corresponding three-dimensional Phi^4 theory with a complex 2N_f x 2N_f symmetric matrix field and symmetry-breaking pattern SU(2N_f)->SO(2N_f). This issue is investigated by exploiting two three-dimensional perturbative approaches, the massless minimal-subtraction scheme without epsilon expansion and a massive scheme in which correlation functions are renormalized at zero momentum. We compute the renormalization-group functions in the two schemes to five and six loops respectively, and determine their large-order behavior. The analyses of the series show the presence of a stable three-dimensional fixed point characterized by the symmetry-breaking pattern SU(4)->SO(4). This fixed point does not appear in an epsilon-expansion analysis and therefore does not exist close to four dimensions. The finite-temperature chiral transition in two-flavor aQCD can therefore be continuous; in this case its critical behavior is determined by this new SU(4)/SO(4) universality class. One-flavor aQCD may show a more complex phase diagram with two phase transitions. One of them, if continuous, should belong to the O(3) vector universality class.Comment: 36 page

On the nature of the finite-temperature transition in QCD

We discuss the nature of the finite-temperature transition in QCD with N_f massless flavors. Universality arguments show that a continuous (second-order) transition must be related to a 3-D universality class characterized by a complex N_f X N_f matrix order parameter and by the symmetry-breaking pattern [SU(N_f)_L X SU(N_f)_R]/Z(N_f)_V -> SU(N_f)_V/Z(N_f)_V, or [U(N_f)_L X U(N_f)_R]/U(1)_V -> U(N_f)_V/U(1)_V if the U(1)_A symmetry is effectively restored at T_c. The existence of any of these universality classes requires the presence of a stable fixed point in the corresponding 3-D Phi^4 theory with the expected symmetry-breaking pattern. Otherwise, the transition is of first order. In order to search for stable fixed points in these Phi^4 theories, we exploit a 3-D perturbative approach in which physical quantities are expanded in powers of appropriate renormalized quartic couplings. We compute the corresponding Callan-Symanzik beta-functions to six loops. We also determine the large-order behavior to further constrain the analysis. No stable fixed point is found, except for N_f=2, corresponding to the symmetry-breaking pattern [SU(2)_L X SU(2)_R]/Z(2)_V -> SU(2)_V/Z(2)_V equivalent to O(4) -> O(3). Our results confirm and put on a firmer ground earlier analyses performed close to four dimensions, based on first-order calculations in the framework of the epsilon=4-d expansion. These results indicate that the finite-temperature phase transition in QCD is of first order for N_f>2. A continuous transition is allowed only for N_f=2. But, since the theory with symmetry-breaking pattern [U(2)_L X U(2)_R]/U(1)_V -> U(2)_V/U(1)_V does not have stable fixed points, the transition can be continuous only if the effective breaking of the U(1)_A symmetry is sufficiently large.Comment: 30 pages, 3 figs, minor correction

What is the prevalence of fear of cancer recurrence in cancer survivors and patients?:A systematic review and individual participant data meta-analysis

OBJECTIVE: Care for fear of cancer recurrence (FCR) is considered the most common unmet need among cancer survivors. Yet the prevalence of FCR and predisposing factors remain inconclusive. To support targeted care, we provide a comprehensive overview of the prevalence and severity of FCR among cancer survivors and patients, as measured using the short form of the validated Fear of Cancer Recurrence Inventory (FCRI-SF). We also report on associations between FCR and clinical and demographic characteristics. METHODS: This is a systematic review and individual participant data (IPD) meta-analysis on the prevalence of FCR. In the review, we included all studies that used the FCRI-SF with adult (≥18 years) cancer survivors and patients. Date of search: 7 February 2020. Risk of bias was assessed using the Joanna Briggs Institute critical appraisal tool. RESULTS: IPD were requested from 87 unique studies and provided for 46 studies comprising 11,226 participants from 13 countries. 9311 respondents were included for the main analyses. On the FCRI-SF (range 0-36), 58.8% of respondents scored ≥13, 45.1% scored ≥16 and 19.2% scored ≥22. FCR decreased with age and women reported more FCR than men. FCR was found across cancer types and continents and for all time periods since cancer diagnosis. CONCLUSIONS: FCR affects a considerable number of cancer survivors and patients. It is therefore important that healthcare providers discuss this issue with their patients and provide treatment when needed. Further research is needed to investigate how best to prevent and treat FCR and to identify other factors associated with FCR. The protocol was prospectively registered (PROSPERO CRD42020142185)

Calorimetric investigation of phase transitions in butyloxybenzylidene heptylaniline (4O.7)

An ac calorimetric study of the phase transitions in butyloxybenzylidene heptylaniline (40.7) shows several interesting differences from the behaviour in the homolog 40. 8. The magnitude of the Cp peak associated with the nematic-smectic-A transition is much smaller in 40.7, as expected since the nematic range is greater, and the effective critical exponent α is smaller in 40.7 than in 40.8. Furthermore, there is a very small Cp peak in 40. 7 just above the melting transition from the B phase to the smectic-A liquid crystal phase. This peak, which is not present in 40.8, suggests that there may be a narrow range of hexatic smectic-B liquid crystal behaviour in 40.7.Une étude calorimétrique des transitions de phase dans le butyloxybenzylidène heptylaniline (40. 7) fait apparaitre des comportements différents de ceux de son homologue (40.8). L'amplitude du pic de chaleur spécifique C p associé à la transition nématique-smectique A est bien plus faible pour (40. 7) où le domaine nématique est plus important, et l'exposant critique effectif α est plus faible pour (40.7) que pour (40.8). En outre, on observe, sur (40. 7), un faible pic de Cp juste au-dessus de la transition de fusion de la phase B à la phase smectique A. Ce pic, non observé pour (40.8), permet de supposer que, dans une plage étroite, (40.7) peut se comporter comme un cristal liquide smectique B hexatique

Critical heat capacity of octylcyanobiphenyl (8CB) near the nematic-smectic A transition

An ac technique has been used to measure the heat capacity near the nematic-smectic A (N-SmA) transition in 8CB along isobars at 1, 750 and 1 500 bar. As the pressure is increased, the magnitude of the Cp peak associated with this transition decreases but the shape of the peak remains essentially unchanged. The excess heat capacity at 1 atm. is consistent with a second-order N-SmA transition characterized by an effective critical exponent α = 0.30 ± 0.05.La technique ac a été utilisée pour mesurer la capacité calorifique près de la transition nématiquesmectique A (N-SmA) du composé 8CB le long d'isobars à 1, 750 et 1 500 bar. La grandeur du pic Cp associé à cette transition décroît quand la pression augmente mais la forme du pic reste essentiellement inchangée. La capacité calorifique en excès à 1 atm. est conforme à une transition N-SmA du second ordre, caractérisée par un exposant critique effectif α = 0,30 ± 0,05

Calorimetric study of phase transitions in the liquid crystal butyloxybenzylidene octylaniline (4O.8)

The heat capacity of butyloxybenzylidene octylaniline has been measured from 0° to 95 °C. Significant pretransitional effects are observed near both the first-order transition from the normal rigid crystal to the B phase plastic crystal and the first-order melting transition from the B phase to the smectic-A liquid crystal phase. Data near the second-order smectic-A to nematic transition require a critical exponent α considerably greater than zero, in agreement with recent results on other materials.La capacité calorifique du butyloxybenzylidène octylaniline a été mesurée entre 0° et 95 °C. Des effets prétransitionnels significatifs sont observés non seulement près de la transition du premier ordre entre le cristal rigide normal et la phase cristalline plastique B mais encore près de la transition de fusion du premier ordre entre la phase B et la phase cristal liquide smectique A. Les données au voisinage de la transition du second ordre smectique A-nématique déterminent un exposant critique α très supérieur à zéro, en accord avec des résultats récents obtenus sur d'autres matériaux