Spiral order by disorder and lattice nematic order in a frustrated Heisenberg antiferromagnet on the honeycomb lattice

Motivated by recent experiments on Bi$_3$Mn$_4$O$_{12}$(NO$_3$), we study a frustrated $J_1$-$J_2$ Heisenberg model on the two dimensional (2D) honeycomb lattice. The classical $J_1$-$J_2$ Heisenberg model on the two dimensional (2D) honeycomb lattice has N\'eel order for $J_2 J_1/6$, it exhibits a one-parameter family of degenerate incommensurate spin spiral ground states where the spiral wave vector can point in any direction. Spin wave fluctuations at leading order lift this accidental degeneracy in favor of specific wave vectors, leading to spiral order by disorder. For spin $S=1/2$, quantum fluctuations are, however, likely to be strong enough to melt the spiral order parameter over a wide range of $J_2/J_1$. Over a part of this range, we argue that the resulting state is a valence bond solid (VBS) with staggered dimer order - this VBS is a nematic which breaks lattice rotational symmetry. Our arguments are supported by comparing the spin wave energy with the energy of the dimer solid obtained using a bond operator formalism. Turning to the effect of thermal fluctuations on the spiral ordered state, any nonzero temperature destroys the magnetic order, but the discrete rotational symmetry of the lattice remains broken resulting in a thermal analogue of the nematic VBS. We present arguments, supported by classical Monte Carlo simulations, that this nematic transforms into the high temperature symmetric paramagnet via a thermal phase transition which is in the universality class of the classical 3-state Potts (clock) model in 2D. We discuss the possible relevance of our results for honeycomb magnets, such as Bi$_3$M$_4$O$_{12}$(NO$_3$) (with M=Mn,V,Cr), and bilayer triangular lattice magnets.Comment: Slightly revise

Sound Level Measurement, Monitoring and Management in Small Music Venues: Leq Averaging Time Interval

This paper considers different Leq averaging time intervals and their effect on the dynamic range of live music as presented to an audience. Data was collected in four small and mid-sized music venues in Perth, Australia in 2019, and combined with an earlier data set recorded in similar venues in Melbourne in 2016. Sound Pressure Level (SPL) data was collected at the Front of House (FOH) sound mixing desk location. In the first phase (control) data was recorded without giving the sound engineer access to sound level information. In the second, phase (experimental), the sound engineer did have visual access to the real time data. This study was designed as a follow-up to earlier work that took place in six music venues in Melbourne [1]. That study concluded that the availability of real time measurement data to sound engineers at the mixing desk can help to keep sound levels below a set maximum. That study also pointed out that if a reduction of the sound exposure of audience and staff is sought, rather than adhering to a prescribed maximum level, more specific choices in terms of level and Leq time interval should be made. Two research questions are considered in this paper, one focused on the impact of the Leq averaging time interval on dynamic range and a second question considering whether set maxima can inadvertently increase the sound levels of performances that would ordinarily be lower than a set maximum level

Calcium signalling links MYC to NUAK1

NUAK1 is a member of the AMPK-related family of kinases. Recent evidence suggests that NUAK1 is an important regulator of cell adhesion and migration, cellular and organismal metabolism, and regulation of TAU stability. As such, NUAK1 may play key roles in multiple diseases ranging from neurodegeneration to diabetes and metastatic cancer. Previous work revealed a crucial role for NUAK1 in supporting viability of tumour cells specifically when MYC is overexpressed. This role is surprising, given that NUAK1 is activated by the tumour suppressor LKB1. Here we show that, in tumour cells lacking LKB1, NUAK1 activity is maintained by an alternative pathway involving calcium-dependent activation of PKCα. Calcium/PKCα-dependent activation of NUAK1 supports engagement of the AMPK-TORC1 metabolic checkpoint, thereby protecting tumour cells from MYC-driven cell death, and indeed, MYC selects for this pathway in part via transcriptional regulation of PKCα and ITPR. Our data point to a novel role for calcium in supporting tumour cell viability and clarify the synthetic lethal interaction between NUAK1 and MYC

The Effect of the Outer Lindblad Resonance of the Galactic Bar on the Local Stellar Velocity Distribution

Hydro-dynamical modeling of the inner Galaxy suggest that the radius of the outer Lindblad resonance (OLR) of the Galactic bar lies in the vicinity of the Sun. How does this resonance affect the distribution function in the outer parts of a barred disk, and can we identify any effect of the resonance in the velocity distribution f(v) actually observed in the solar neighborhood? To answer these questions, detailed simulations of f(v) in the outer parts of an exponential stellar disks with nearly flat rotation curves and a rotating central bar have been performed. For a model resembling the old stellar disk, the OLR causes a distinct feature in f(v) over a significant fraction of the outer disk. For positions <2kpc outside the OLR radius and at bar angles of \~10-70 degrees, f(v) inhibits a bi-modality between the low-velocity stars moving like the local standard of rest (LSR) and a secondary mode of stars predominantly moving outward and rotating more slowly than the LSR. Such a bi-modality is indeed present in f(v) inferred from the Hipparcos data for late-type stars in the solar neighborhood. If one interpretes this observed bi-modality as induced by the OLR -- and there are hardly any viable alternatives -- then one is forced to deduce that the OLR radius is slightly smaller than Ro. Moreover, by a quantitative comparison of the observed with the simulated distributions one finds that the pattern speed of the bar is 1.85+/-0.15 times the local circular frequency, where the error is dominated by the uncertainty in bar angle and local circular speed. Also other, less prominent but still significant, features in the observed f(v) resemble properties of the simulated velocity distributions, in particular a ripple caused by orbits trapped in the outer 1:1 resonance.Comment: 14 pages, 10 figures (Fig.2 in full resolution available upon request), accepted for publication in A

The Art of Distancing: A Review of How to Do Nothing

In this symposium style review, Matt Drissell (Associate Professor of Art), Leah Zuidema (Vice President for Online & Graduate Education), and Dave Mulder (Associate Professor of Education) each bring perspectives from their area of expertise. Posting about the book How to Do Nothing-Resisting the Attention Economy from In All Things - an online journal for critical reflection on faith, culture, art, and every ordinary-yet-graced square inch of God’s creation. https://inallthings.org/the-art-of-distancing-a-review-of-how-to-do-nothing

The influence of audience participatory noise on sound levels at live events

Although the importance of audience participation at events, in terms of verbal and non-verbal appreciation, is well recognised, the by-product, noise, primarily in the form of applause, cheering and whistling, has been subject to little study in terms of its impact on sound pressure levels. This paper presents findings from a preliminary study in this area, where the specific impact of audiences on overall sound levels is analysed using a dataset from real-world large-scale events. Results indicate that an audience is capable of significantly increasing an event's overall sound level, even though their active participation only constitutes a small proportion of the event duration. Since sound level limits do not distinguish between noise sources, this notable influence from the audience can prevent compliance with imposed limits and should be considered in future updates to sound level monitoring systems and standards/regulations

Assessing recovery after cold challenge and thumb involvement can help to rule out systemic sclerosis in patients presenting with Raynaud?s phenomenon

Objective: Our aim was to study whether recovery from a Raynaud?s attack and involvement of the thumb are differentiators for systemic sclerosis (SSc) in patients with Raynaud?s phenomenon (RP). Method: A stepwise cooling and recovery procedure was performed, provoking an RP attack, in patients with primary Raynaud?s phenomenon (PRP, n =?68) and SSc (n?=?18). During the procedure, the perfusion of all five fingers during cooling and recovery was assessed by photoelectric plethysmography. Results: In SSc patients, perfusion after 10?min in one or more fingers was more frequently not restored than in PRP patients (p?=?0.001), with a negative predictive value of 98%. The thumb was more frequently involved in SSc patients (p?=?0.036), with a negative predictive value of 95%. Positive predictive values were low. Conclusions: In patients with RP, when there is restoration of perfusion in all fingers after 10?min or when the thumb is spared, the presence of an underlying SSc is very unlikely. Although these results need to be validated in a clinical setting in a larger prospective study, these signs can help physicians to select additional testing for SSc in RP patients