The extension of the cosmic-ray spectrum beyond 1 petaelectronvolt (PeV; 10
electronvolts) indicates the existence of the so-called PeVatrons-cosmic-ray factories that accelerate particles to PeV ...energies. We need to locate and identify such objects to find the origin of Galactic cosmic rays
. The principal signature of both electron and proton PeVatrons is ultrahigh-energy (exceeding 100 TeV) γ radiation. Evidence of the presence of a proton PeVatron has been found in the Galactic Centre, according to the detection of a hard-spectrum radiation extending to 0.04 PeV (ref.
). Although γ-rays with energies slightly higher than 0.1 PeV have been reported from a few objects in the Galactic plane
, unbiased identification and in-depth exploration of PeVatrons requires detection of γ-rays with energies well above 0.1 PeV. Here we report the detection of more than 530 photons at energies above 100 teraelectronvolts and up to 1.4 PeV from 12 ultrahigh-energy γ-ray sources with a statistical significance greater than seven standard deviations. Despite having several potential counterparts in their proximity, including pulsar wind nebulae, supernova remnants and star-forming regions, the PeVatrons responsible for the ultrahigh-energy γ-rays have not yet been firmly localized and identified (except for the Crab Nebula), leaving open the origin of these extreme accelerators.
During the consumption of alkanes,
Alcanivorax borkumensis
will form a biofilm around an oil droplet, but the role this plays during degradation remains unclear. We identified a shift in biofilm ...morphology that depends on adaptation to oil consumption: Longer exposure leads to the appearance of dendritic biofilms optimized for oil consumption effected through tubulation of the interface. In situ microfluidic tracking enabled us to correlate tubulation to localized defects in the interfacial cell ordering. We demonstrate control over droplet deformation by using confinement to position defects, inducing dimpling in the droplets. We developed a model that elucidates biofilm morphology, linking tubulation to decreased interfacial tension and increased cell hydrophobicity.
Editor’s summary
Certain marine bacteria can degrade small-molecule hydrocarbons, but there is still limited understanding on how this process works in biofilms. Prasad
et al
. show that one such bacterium,
Alcanivorax borkumensis
, initially forms a spherical biofilm around a droplet of hexadecane, which subsequently grows and buckles (see the Perspective by McGenity and Laissue). This transition is caused by an initial limited interaction with the oil by only some of the cells, followed by rapid cell growth and division that distorts the shape of the biofilm, leading to an increase in the surface area and acceleration in the rate of consumption. Adhesion of aligned rod-shaped bacterial cells to the oil stabilizes the tube-like protrusions. The addition of surfactants commonly used to disperse marine oil spills disrupts the biofilms, and the cells return to their spherical morphology. —Marc S. Lavine
A type of oil-eating bacteria adapts its biofilm interfacial properties to accelerate the rate of oil consumption.
Abstract
Bulk Bi
0.5
Sr
0.5
Fe
0.5
Cr
0.5
O
3
(BSFCO) is a new compound comprising the
R3c
structure. The structural, magnetic property and exchange bias (EB) details are investigated. The material ...was in the super-paramagnetic (SP) state at room temperature. Exchange bias usually occurs at the boundary between different magnetic states after field cooling (
H
FC
) acts on the sample. Here the result shows that changing
H
FC
from 1 to 6 T reduces the
H
EB
value by 16% at 2 K at the same time. Meanwhile,
H
EB
diminishes as the ferromagnetic layer thickness increases. The variation of (the thickness of ferromagnetic layer)
t
FM
with the change of
H
FC
leads to the tuning of
H
EB
by
H
FC
in BSFCO bulk. These effects are obviously different from the phenomenon seen in other oxide types.
► DMS-PSO-HS takes merits of the PSO and the HS. ► DMS-PSO-HS avoids all particles getting trapped in inferior local optimal regions. ► DMS-PSO-HS regroups the sub-swarms frequently. ► DMS-PSO-HS ...forms new harmonies to search in a larger search space.
In this paper, the dynamic multi-swarm particle swarm optimizer (DMS-PSO) is improved by hybridizing it with the harmony search (HS) algorithm and the resulting algorithm is abbreviated as DMS-PSO-HS. We present a novel approach to merge the HS algorithm into each sub-swarm of the DMS-PSO. Combining the exploration capabilities of the DMS-PSO and the stochastic exploitation of the HS, the DMS-PSO-HS is developed. The whole DMS-PSO population is divided into a large number of small and dynamic sub-swarms which are also individual HS populations. These sub-swarms are regrouped frequently and information is exchanged among the particles in the whole swarm. The DMS-PSO-HS demonstrates improved on multimodal and composition test problems when compared with the DMS-PSO and the HS.
High-energy photons from the Crab Nebula
The Crab Nebula contains a pulsar that excites the surrounding gas to emit high-energy radiation. The combination of the pulsar's youth and nearby location ...makes the nebula the brightest gamma-ray source in the sky. The LHAASO Collaboration report observations of this source at energies of tera– to peta–electron volts, extending the spectrum of this prototypical object. They combine these data with observations at lower energies to model the physics of the emission process. The multiwave-length data can be explained by a combination of synchrotron radiation and inverse Compton scattering.
Science
, abg5137, this issue p.
425
Detection of the Crab Nebula at peta–electron volt energies constrains the gamma-ray emission mechanism.
The Crab Nebula is a bright source of gamma rays powered by the Crab Pulsar’s rotational energy through the formation and termination of a relativistic electron-positron wind. We report the detection of gamma rays from this source with energies from 5 × 10
−4
to 1.1 peta–electron volts with a spectrum showing gradual steepening over three energy decades. The ultrahigh-energy photons imply the presence of a peta–electron volt electron accelerator (a pevatron) in the nebula, with an acceleration rate exceeding 15% of the theoretical limit. We constrain the pevatron’s size between 0.025 and 0.1 parsecs and the magnetic field to ≈110 microgauss. The production rate of peta–electron volt electrons, 2.5 × 10
36
ergs per second, constitutes 0.5% of the pulsar spin-down luminosity, although we cannot exclude a contribution of peta–electron volt protons to the production of the highest-energy gamma rays.
Free-electron lasers have been successfully operated with ultrahigh brightness and excellent transverse coherence at X-ray wavelengths. One of the next goals for further improvements is full ...coherence. An obvious approach is to seed the free-electron laser interaction using a conventional source that has good temporal coherence. Here, we show the first lasing of a free-electron laser with an echo-enabled harmonic generation scheme, which shows great promise for producing coherent lasing at short wavelengths, even in the X-ray regime. The experiment was conducted at a test facility that combines a 135.4 MeV electron accelerator with an amplifier consisting of a series of undulator magnets. Lasing was achieved at the third harmonic of the seed with a gain of ∼100,000 over spontaneous radiation. The measurements show typical exponential growth and excellent spectral characteristics, as well as good intensity stability.
In this paper, two
lbests multi-objective particle swarm optimization (2LB-MOPSO) is applied to design multi-objective robust Proportional-integral-derivative (PID) controllers for two MIMO systems, ...namely, distillation column plant and longitudinal control system of the super maneuverable F18/HARV fighter aircraft. Multi-objective robust PID controller design problem is formulated by minimizing integral squared error (ISE) and balanced robust performance criteria. During the search, 2LB-MOPSO can focus on small regions in the parameter space in the vicinity of the best existing fronts. As the
lbests are chosen from the top fronts in a non-domination sorted external archive of reasonably large size, the offspring obtained can be more diverse with good fitness. The performance of various optimal PID controllers is compared in terms of the sum of ISE and balanced robust performance criteria. For the purpose of comparison, 2LB-MOPSO, NSGA-II as well as earlier reported Riccati, IGA and OSA methods are considered. The performance of PID controllers obtained using 2LB-MOPSO is better than that of others. In addition, Hypervolume-based comparisons are carried out to show the superior performance of 2LB-MOPSO over NSGA-II. The results reveal that 2LB-MOPSO yields better robustness and consistency in terms of the sum of ISE and balanced robust performance criteria than various optimal PID controllers.
Aliment Pharmacol Ther 2011; 34: 1020–1029
Summary
Background The epidemiology and effects of functional constipation (FC) on Chinese people remain unclear.
Aim To investigate the epidemiology of ...FC and its distinction from constipation‐predominant irritable bowel syndrome (IBS‐C) in China.
Methods A cross‐sectional survey was conducted in a representative adult Chinese population (n = 16 078), which was selected from five regions using randomised, stratified, multistage sampling methodology. All respondents completed the modified Rome II questionnaire; 20% were asked to complete the 36‐item Short Form (SF‐36) and the Epworth Sleepiness Scale (ESS).
Results Overall, 948 respondents (6%) had FC and FC was more prevalent in women than in men (8% vs. 4%, P < 0.001). Straining and hard stools were the two most frequent symptoms. FC was associated significantly with dyspepsia and abdominal bloating. All SF‐36 domain scores were lower for respondents with FC than for those without. The prevalence of clinically meaningful daytime sleepiness was significantly higher in respondents with FC than in those without (22% vs. 14%, P = 0.003). Respondents with FC were more likely to strain, but less likely to have a feeling of incomplete emptying after a bowel movement than those with IBS‐C. Respondents with IBS‐C experienced similar demographics, quality of life and daytime sleepiness to those with FC.
Conclusions The prevalence of FC in China is substantially lower than that in Western countries. FC has negative effects on quality of life and daytime sleepiness. The demographics and burden of illness are similar between FC and IBS‐C, although the clinical symptoms are somewhat different.
The object of this paper was to explore the feasibility and advantages of endoscope-assisted parotid tumour resection. Three databases (PubMed, Web of Science, and Cochrane) were used to search for ...all related randomised controlled trials or controlled trials (up to November 2019). The key parameters for assessment included ‘Endoscope’, ‘Endoscopes’, ‘Cancer of Parotid’, and ‘Parotid Cancer’. To evaluate the feasibility and advantages of endoscope-assisted resection of parotid tumours, the data for each parameter were pooled, based on patients who received endoscope-assisted surgery and those who received conventional surgery. This meta-analysis included seven studies, involving 170 patients in the endoscopy group and 270 patients in the control group. The analysis using the pooled data showed that there were no significant differences in the operating times between the two groups; however, the endoscopy group had significantly shorter incisions and less intraoperative bleeding. In addition, the patients who received endoscope-assisted surgery had lower incidences of temporary facial paralysis and Frey’s syndrome after surgery. Patients in the endoscopy group had greater postoperative satisfaction. Endoscope-assisted parotid tumour resection results in only a small, concealed incision wound and fewer postoperative complications. Therefore, it is promising for the surgical treatment of parotid tumours.
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