A radio ridge connecting two galaxy clusters in a filament of the cosmic web.

Galaxy clusters are the most massive gravitationally bound structures in the Universe. They grow by accreting smaller structures in a merging process that produces shocks and turbulence in the intracluster gas. We observed a ridge of radio emission connecting the merging galaxy clusters Abell 0399 and Abell 0401 with the Low-Frequency Array (LOFAR) telescope network at 140 megahertz. This emission requires a population of relativistic electrons and a magnetic field located in a filament between the two galaxy clusters. We performed simulations to show that a volume-filling distribution of weak shocks may reaccelerate a preexisting population of relativistic particles, producing emission at radio wavelengths that illuminates the magnetic ridge.

Needle-like structures discovered on positively charged lightning branches.

Lightning is a dangerous yet poorly understood natural phenomenon. Lightning forms a network of plasma channels propagating away from the initiation point with both positively and negatively charged ends-called positive and negative leaders1. Negative leaders propagate in discrete steps, emitting copious radio pulses in the 30-300-megahertz frequency band2-8 that can be remotely sensed and imaged with high spatial and temporal resolution9-11. Positive leaders propagate more continuously and thus emit very little high-frequency radiation12. Radio emission from positive leaders has nevertheless been mapped13-15, and exhibits a pattern that is different from that of negative leaders11-13,16,17. Furthermore, it has been inferred that positive leaders can become transiently disconnected from negative leaders9,12,16,18-20, which may lead to current pulses that both reconnect positive leaders to negative leaders11,16,17,20-22 and cause multiple cloud-to-ground lightning events1. The disconnection process is thought to be due to negative differential resistance18, but this does not explain why the disconnections form primarily on positive leaders22, or why the current in cloud-to-ground lightning never goes to zero23. Indeed, it is still not understood how positive leaders emit radio-frequency radiation or why they behave differently from negative leaders. Here we report three-dimensional radio interferometric observations of lightning over the Netherlands with unprecedented spatiotemporal resolution. We find small plasma structures-which we call 'needles'-that are the dominant source of radio emission from the positive leaders. These structures appear to drain charge from the leader, and are probably the reason why positive leaders disconnect from negative ones, and why cloud-to-ground lightning connects to the ground multiple times.

The analgesic effects of intrathecal morphine in comparison with ultrasound-guided transversus abdominis plane block after caesarean section: a randomised controlled trial at a Ugandan regional referral hospital.

Both transversus abdominis plane block and intrathecal morphine may produce prolonged postoperative analgesia, but the respective clinical outcomes of these anaesthetic techniques in resource-limited settings are not well described. We randomly assigned patients undergoing caesarean section to receive a hyperbaric bupivacaine (10 mg) spinal anaesthetic followed by an ultrasound-guided transversus abdominis plane block, or a hyperbaric bupivacaine (10 mg) spinal anaesthetic with 100 mcg intrathecal morphine, followed by a postoperative sham block. Supplemental postoperative analgesia included self-administered oral diclofenac 50 mg and paracetamol 1 g every 8 h. Numerical pain rating scores, the need for rescue medication, side-effects and patient satisfaction were recorded at 8, 16 and 24 h. We enrolled a total of 130 patients, with 65 women in each group. The mean numerical rating score for intrathecal morphine vs. transversus abdominis plane blocks at 8 h were: at rest, 2.5 vs. 3.1 (p = 0.04); with coughing, 4.3 vs. 4.8 (p = 0.07); and with movement, 3.6 vs. 4.2 (p = 0.06). At 16 h, respective scores were: 2.9 vs. 3.1 (p = 0.40) at rest; 4.0 vs. 4.3 (p = 0.19) with coughing; and 4.8 vs. 5.0 (p = 0.33) with movement. At 24 h, the respective scores were: 2.9 vs. 2.3 (p = 0.01); 4.6 vs. 4.2 (p = 0.04) with coughing; and 3.9 vs. 3.4 (p = 0.02) with movement. The need for rescue medication and the incidence of pruritis, sedation and nausea and vomiting were similar in both groups. Patient satisfaction with pain control was similar in both groups, with the majority of patients reporting satisfaction as good or excellent. Intrathecal morphine and transversus abdominis plane block provided clinically similar outcomes for pain relief after caesarean section.

A large light-mass component of cosmic rays at 10(17)-10(17.5) electronvolts from radio observations.

Cosmic rays are the highest-energy particles found in nature. Measurements of the mass composition of cosmic rays with energies of 10(17)-10(18) electronvolts are essential to understanding whether they have galactic or extragalactic sources. It has also been proposed that the astrophysical neutrino signal comes from accelerators capable of producing cosmic rays of these energies. Cosmic rays initiate air showers--cascades of secondary particles in the atmosphere-and their masses can be inferred from measurements of the atmospheric depth of the shower maximum (Xmax; the depth of the air shower when it contains the most particles) or of the composition of shower particles reaching the ground. Current measurements have either high uncertainty, or a low duty cycle and a high energy threshold. Radio detection of cosmic rays is a rapidly developing technique for determining Xmax (refs 10, 11) with a duty cycle of, in principle, nearly 100 per cent. The radiation is generated by the separation of relativistic electrons and positrons in the geomagnetic field and a negative charge excess in the shower front. Here we report radio measurements of Xmax with a mean uncertainty of 16 grams per square centimetre for air showers initiated by cosmic rays with energies of 10(17)-10(17.5) electronvolts. This high resolution in Xmax enables us to determine the mass spectrum of the cosmic rays: we find a mixed composition, with a light-mass fraction (protons and helium nuclei) of about 80 per cent. Unless, contrary to current expectations, the extragalactic component of cosmic rays contributes substantially to the total flux below 10(17.5) electronvolts, our measurements indicate the existence of an additional galactic component, to account for the light composition that we measured in the 10(17)-10(17.5) electronvolt range.

Probing Atmospheric Electric Fields in Thunderstorms through Radio Emission from Cosmic-Ray-Induced Air Showers.

We present measurements of radio emission from cosmic ray air showers that took place during thunderstorms. The intensity and polarization patterns of these air showers are radically different from those measured during fair-weather conditions. With the use of a simple two-layer model for the atmospheric electric field, these patterns can be well reproduced by state-of-the-art simulation codes. This in turn provides a novel way to study atmospheric electric fields.

Sonohysterography in premenopausal women with and without abnormal bleeding.

OBJECTIVE: To estimate the prevalence of abnormalities detected by sonohysterography in premenopausal women who were asymptomatic or had abnormal uterine bleeding. METHODS: Standard sonohysterography was done in 100 asymptomatic premenopausal women age 30 and older. The prevalence of uterine abnormalities was recorded and compared with findings in 80 premenopausal women evaluated in our unit for abnormal uterine bleeding. RESULTS: Compared with asymptomatic women, premenopausal women with abnormal uterine bleeding had a higher prevalence of polyps (33 versus 10%), intracavitary myomas (21 versus 1%), and intramural myomas (58 versus 13%). Ten percent of asymptomatic women had polyps, but these polyps tended to be smaller than the polyps found in women with abnormal bleeding (8.5 versus 13.9 mm, P = .064). Polyps were associated significantly with myomas, and both were more common in older premenopausal women. CONCLUSION: Intracavitary lesions and intramural myomas are more prevalent in women with abnormal uterine bleeding than in asymptomatic women, suggesting a causative relationship. However, small endometrial polyps are common and frequently asymptomatic.