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Using weapons instead of perfume: chemical association strategies of the myrmecophilous bug Scolopostethus pacificus (Rhyparochromidae)
No full textA vast diversity of parasites associates with ants. Living in and around ant nests of these organisms must overcome ant colony defenses. As ant defensive behavior is mainly mediated by species-specific cuticular hydrocarbons (CHCs) or alarm pheromones, and ant-associated parasites can either crack their hosts’ chemical communication code by modifying their own CHC profiles or use pro-active strategies like chemical weaponry for distraction and repellency. While the chemical nature of ant–parasite interactions has been intensively studied for highly host-specific parasites, the chemical-deceptive strategies of the rather rare ant-resembling heteropterans are unknown. To gain insight into this system, I studied the bug Scolopostethus pacificus (Barber 1918) which can be found near the nests of the ecologically dominant and aggressive velvety tree ant (Liometopum occidentale, Emery 1895). Using behavioral, chemical, and molecular approaches, I disentangled the relationship of S. pacificus and its host ant. Chemical profiling of the bug and the ant revealed that the bug does not make use of CHC insignificance or mimicry, but instead uses a cocktail of volatile compounds released from its metathoracic glands that likely moderates encounters with its aggressive host. Feeding trials with armed and artificially disarmed bugs revealed a defensive function of the gland exudates. Targeted molecular gut barcoding showed that S. pacificus does not feed on L. occidentale. These results suggest that chemical weaponry, rather than a chemical code-cracking CHC matching or chemical insignificance, enables S. pacificus to get along with and live in close proximity to its host ant
SpatioTemporally Adaptive Quadtree Mesh (STAQ) Digital Image Correlation for Resolving Large Deformations Around Complex Geometries and Discontinuities
No full textBackground. Digital image correlation (DIC) is a powerful experimental tool for measuring full-field material deformations. Inherent limitations of typical DIC algorithms can cause a multitude of errors when analyzing the displacement field of samples containing complex geometries or discontinuities. Most adaptations rely on either splitting or augmenting the local DIC subsets that pass through the discontinuity path. However, these methods are challenging to generalize and automate, often requiring significant user intervention.
Objective. To address these shortcomings, we present a new, user-friendly automatic experimental approach for resolving the deformation fields around complex geometries and displacement discontinuities, which we call the spatiotemporally adaptive quadtree mesh (STAQ) DIC method.
Methods. In this method, the adaptive quadtree mesh is automatically generated from a mask file of the DIC image itself to handle the inherent complex geometry. Subsets that span either geometric or displacement discontinuities are automatically split to improve their DIC accuracy. A binary image mask is also used to inform an interpolation scheme for displacement and strain calculations. Furthermore, we also propose a data-driven reduced order modeling (ROM) approach to further reduce the computational costs by skipping unnecessary image frames thus achieving temporal adaptability for efficiently processing large image sequences.
Results. We demonstrate that our STAQ method has high accuracy in solving complex geometric and discontinuous deformation fields in an automated fashion. We find that the proposed data-driven ROM method can provide up to 60% in computational cost savings while maintaining the same level of accuracy compared to a fully processed image set.
Conclusions. STAQ DIC is a computationally efficient method for accurately solving geometrically complex and discontinuous deformation fields. Using the data-driven ROM method as part of STAQ can further reduce computational costs for processing large image sequences. An open-source Matlab implementation is freely available
Investigating the Nature of the Luminous Ambiguous Nuclear Transient ASASSN-17jz
No full textWe present observations of the extremely luminous but ambiguous nuclear transient (ANT) ASASSN-17jz, spanning roughly 1200 days of the object’s evolution. ASASSN-17jz was discovered by the All-Sky Automated Survey for Supernovae (ASAS-SN) in the galaxy SDSS J171955.84+414049.4 on UT 2017 July 27 at a redshift of z = 0.1641. The transient peaked at an absolute B-band magnitude of M_(B,peak) = −22.81, corresponding to a bolometric luminosity of L_(bol,peak) = 8.3 × 10⁴⁴ erg s⁻¹, and exhibited late-time ultraviolet emission that was still ongoing in our latest observations. Integrating the full light curve gives a total emitted energy of E_(tot) = (1.36 ±0.08) × 10⁵² erg, with (0.80 ± 0.02) × 10⁵² erg of this emitted within 200 days of peak light. This late-time ultraviolet emission is accompanied by increasing X-ray emission that becomes softer as it brightens. ASASSN-17jz exhibited a large number of spectral emission lines most commonly seen in active galactic nuclei (AGNs) with little evidence of evolution. It also showed transient Balmer features, which became fainter and broader over time, and are still being detected >1000 days after peak brightness. We consider various physical scenarios for the origin of the transient, including supernovae (SNe), tidal disruption events, AGN outbursts, and ANTs. We find that the most likely explanation is that ASASSN-17jz was a SN IIn occurring in or near the disk of an existing AGN, and that the late-time emission is caused by the AGN transitioning to a more active state
Discovery of a Novel Inner Membrane-Associated Bacterial Structure Related to the Flagellar Type III Secretion System
No full textThe bacterial flagellar type III secretion system (fT3SS) is a suite of membrane-embedded and cytoplasmic proteins responsible for building the flagellar motility machinery. Homologous nonflagellar (NF-T3SS) proteins form the injectisome machinery that bacteria use to deliver effector proteins into eukaryotic cells, and other family members were recently reported to be involved in the formation of membrane nanotubes. Here, we describe a novel, evolutionarily widespread, hat-shaped structure embedded in the inner membranes of bacteria, of yet-unidentified function, that is present in species containing fT3SS. Mutant analysis suggests a relationship between this novel structure and the fT3SS, but not the NF-T3SS. While the function of this novel structure remains unknown, we hypothesize that either some of the fT3SS proteins assemble within the hat-like structure, perhaps including the fT3SS core complex, or that fT3SS components regulate other proteins that form part of this novel structure
Monitoring observations of SMC X-1’s excursions (MOOSE)–I. Programme description and initial high state spectral results
No full textSMC X-1 has exhibited three superorbital period excursions since the onset of X-ray monitoring beginning with the Rossi X-ray Timing Explorer's launch in 1995. TheNeutron star Interior Composition Explorer has recently probed a fourth observed excursion beginning in 2021 with our programme monitoring observations of SMC X-1’s excursions (moose). These sensitive new moose data probe different superorbital periods and phases within them. Spectral fits to the high-state continuum during 2021 April to 2022 January show that the intrinsic spectral shapes are characterized by a soft (kT ∼ 0.19 keV) disc component and a hard (Γ ∼ 0.7) power-law tail. When the 2021–2022 NICER observations, taken during an excursion, are compared to 2016 XMM–Newton observations (outside of an excursion), we find little evidence for intrinsic spectral variability across the high states, but find evidence for a >3σ change in the absorption, although we caution that there may be calibration differences between the two instruments. Thus, over different lengths of superorbital periods, we see little evidence for intrinsic spectral changes in the high state. Upcoming studies of the pulse profiles may shed light on the mechanism behind the excursions
Computationally-defined markers of uncertainty aversion predict emotional responses during a global pandemic
No full textExposure to stressful life events involving threat and uncertainty often results in the development of anxiety. However, the factors that confer risk and resilience for anxiety following real world stress at a computational level remain unclear. We identified core components of uncertainty aversion moderating response to stress posed by the COVID-19 pandemic derived from computational modeling of decision making. Using both cross-sectional and longitudinal analyses, we investigated both immediate effects at the onset of the stressor, as well as medium-term changes in response to persistent stress. 479 subjects based in the United States completed a decision-making task measuring risk aversion, loss aversion, and ambiguity aversion in the early stages of the pandemic (March 2020). Self-report measures targeting threat perception, anxiety, and avoidant behavior in response to the pandemic were collected at the same time point and 8 weeks later (May 2020). Cross-sectional analyses indicated that higher risk aversion predicted higher perceived threat from the pandemic, and ambiguity aversion for guaranteed gains predicted perceived threat and pandemic-related anxiety. In longitudinal analyses, ambiguity aversion for guaranteed gains predicted greater increases in perceived infection likelihood. Together, these results suggest that individuals who have a low-level aversion toward uncertainty show stronger negative emotional reactions to both the onset and persistence of real-life stress
The minimally conscious state: an analysis of current clinical trials registered in ClinicalTrials.gov
No full textThe minimally conscious state (MCS) is a disorder of consciousness described in recent years for patients who have behavioral responses to stimuli that do not meet the classification of chronic vegetative state (CVS) or coma. This distinction is valuable in clinical practice, as minimally conscious patients may require different treatments and may have different long-term outcomes when compared to vegetative states or coma. In this report, we analyzed the ClinicalTrials.gov database to systematically assess all clinical trials regarding MCS. The database was queried using the term “minimally conscious state” in the “condition or disease” search parameter. Of the studies identified, those that had suspended, terminated, or otherwise unknown statuses were excluded. In total, 41 studies were analyzed. The included studies were initiated between 2008 and 2020, with the majority (63%) beginning in 2015 or later. Of the primary intervention modalities included, 15 (37%) evaluated stimulation modalities such as transcranial magnetic stimulation, transcranial direct current stimulation, implantable neurostimulation, vagus nerve stimulation, focused ultrasound and median nerve stimulation. Additionally, 5 (12%) used some form of behavioral therapy. A total of 4 (10%) studies involved pharmaceutical intervention, including dopamine agonists, analgesics and sedatives. Finally, 4 (10%) studies sought to determine the validity of current diagnostic methods and systems used to assess the status of patients in MCSs. Since the definition and criteria for CVS and MCS have been established, these two conditions remain closely associated despite evidence of different patient outcomes and treatment options. Many clinical trials are underway assessing interventions with stimulation. However, the trials are lacking with respect to diagnostic methods and pharmaceutical treatment
Capacity of the Trapdoor Channel with Delayed Feedback
No full textWe show that the trapdoor channel’s capacity with delayed feedback of two time-instances is given by C₂ᶠᵇ = log₂(3/2).
This demonstrates that the feedback capacity degrades sharply even with a single time-instance delay of the channel outputs. The capacity result is established by showing that the delayed feedback capacity can be formulated as a capacity problem with instantaneous feedback and an extended state. Consequently, graph-based methods can be applied to obtain new computable upper and lower bounds on the capacity, which are shown to coincide for the trapdoor channel
On Algebraic Constructions of Neural Networks with Small Weights
No full textNeural gates compute functions based on weighted sums of the input variables. The expressive power of neural gates (number of distinct functions it can compute) depends on the weight sizes and, in general, large weights (exponential in the number of inputs) are required. Studying the trade-offs among the weight sizes, circuit size and depth is a well-studied topic both in circuit complexity theory and the practice of neural computation. We propose a new approach for studying these complexity trade-offs by considering a related algebraic framework. Specifically, given a single linear equation with arbitrary coefficients, we would like to express it using a system of linear equations with smaller (even constant) coefficients. The techniques we developed are based on Siegel’s Lemma for the bounds, anti-concentration inequalities for the existential results and extensions of Sylvester-type Hadamard matrices for the constructions.We explicitly construct a constant weight, optimal size matrix to compute the EQUALITY function (checking if two integers expressed in binary are equal). Computing EQUALITY with a single linear equation requires exponentially large weights. In addition, we prove the existence of the best-known weight size (linear) matrices to compute the COMPARISON function (comparing between two integers expressed in binary). In the context of the circuit complexity theory, our results improve the upper bounds on the weight sizes for the best-known circuit sizes for EQUALITY and COMPARISON
Third-order Analysis of Channel Coding in the Moderate Deviations Regime
No full textThe channel coding problem in the moderate deviations regime is studied; here, the error probability sub-exponentially decays to zero, and the rate approaches the capacity slower than O(1/√n). The main result refines Altuğ and Wagner’s moderate deviations result by deriving lower and upper bounds on the third-order term in the asymptotic expansion of the maximum achievable message set size. The third-order term of the expansion employs a new quantity called the channel skewness. For the binary symmetric channel and most practically important (n,ϵ) pairs, including n ∈ [100, 500] and ϵ ∈ [10⁻¹⁰,10⁻¹], an approximation up to the channel skewness is the most accurate among several expansions in the literature