Global MHD simulations of Saturns's magnetosphere at the time of Cassini approach

We present the results of a 3D global magnetohydrodynamic simulation of the magnetosphere of Saturn for the period of Cassini's initial approach and entry into the magnetosphere. We compare calculated bow shock and magnetopause locations with the Cassini measurements. In order to match the measured locations we use a substantial mass source due to the icy satellites (\sim1 x 10^{28} s^{-1} of water product ions). We find that the location of bow shock and magnetopause crossings are consistent with previous spacecraft measurements, although Cassini encountered the surfaces further from Saturn than the previously determined average location. In addition, we find that the shape of the model bow shock and magnetopause have smaller flaring angles than previous models and are asymmetric dawn-to-dusk. Finally, we find that tilt of Saturn's dipole and rotation axes results in asymmetries in the bow shock and magnetopause and in the magnetotail being hinged near Titan's orbit (\sim20 R _S)

Quasiperpendicular high Mach number Shocks

Shock waves exist throughout the universe and are fundamental to understanding the nature of collisionless plasmas. Reformation is a process, driven by microphysics, which typically occurs at high Mach number supercritical shocks. While ongoing studies have investigated this process extensively both theoretically and via simulations, their observations remain few and far between. In this letter we present a study of very high Mach number shocks in a parameter space that has been poorly explored and we identify reformation using in situ magnetic field observations from the Cassini spacecraft at 10 AU. This has given us an insight into quasi-perpendicular shocks across two orders of magnitude in Alfven Mach number (MA) which could potentially bridge the gap between modest terrestrial shocks and more exotic astrophysical shocks. For the first time, we show evidence for cyclic reformation controlled by specular ion reflection occurring at the predicted timescale of ~0.3 {\tau}c, where {\tau}c is the ion gyroperiod. In addition, we experimentally reveal the relationship between reformation and MA and focus on the magnetic structure of such shocks to further show that for the same MA, a reforming shock exhibits stronger magnetic field amplification than a shock that is not reforming.Comment: Accepted and Published in Physical Review Letters (2015

Baseball in the heartland: Semi-pro baseball survives in Iowa

Baseball has been an important part of American popular culture for over one hundred years. In the early part of the twentieth century baseball was the nation\u27s most pervasive sport and symbolized many values and attitudes that Americans held dear. During the late nineteenth century, adult baseball teams were formed within small towns across the nation. The team members were typically considered amateur athletes playing town team baseball. Over the years, as they were given opportunities to make money from their play, the term of semi-professional was applied to many of these players. The decades following World War II were a time of growth and great prosperity for semi-pro baseball in Iowa and the rest of the country. During the later decades of the twentieth century, social and historical trends in America caused many towns to lose their local baseball teams. In the early nineteen hundreds nearly every town, large and small, had a team. By the end of the century most towns had lost their teams. In northeast Iowa, however, semi-pro baseball has been able to survive relatively unchanged. Despite the failure of teams across the nation, there are currently two leagues with a total of seventeen teams in existence within a relatively small geographic area. While battling the same undermining trends that weakened baseball\u27s health elsewhere, northeast Iowa has been able to continue to support town baseball. Two key factors in the continued existence of baseball in this area are: sufficient financial resources to sustain the teams and a strong sense of tradition. The tournament structure that has evolved since the late 1940s has given teams in this area the economic security needed to survive. The movie Field of Dreams has given the community of Dyersville a prominent place in the nostalgic mythology of American baseball. However, long before the movie was filmed in the 1980s, Dyersville and other area teams were a part of a strong tradition of semi-pro baseball which has helped to keep town ball alive in northeast Iowa

Quantifying the relative contributions of substorm injections and chorus waves to the rapid outward extension of electron radiation belt

Abstract We study the rapid outward extension of the electron radiation belt on a timescale of several hours during three events observed by Radiation Belt Storm Probes and Time History of Events and Macroscale Interactions during Substorms satellites and particularly quantify the contributions of substorm injections and chorus waves to the electron flux enhancement near the outer boundary of radiation belt. A comprehensive analysis including both observations and simulations is performed for the first event on 26 May 2013. The outer boundary of electron radiation belt moved from L = 5.5 to L \u3e 6.07 over about 6 h, with up to 4 orders of magnitude enhancement in the 30 keV to 5 MeV electron fluxes at L = 6. The observations show that the substorm injection can cause 100% and 20% of the total subrelativistic (∼0.1 MeV) and relativistic (2-5 MeV) electron flux enhancements within a few minutes. The data-driven simulation supports that the strong chorus waves can yield 60%-80% of the total energetic (0.2-5.0 MeV) electron flux enhancement within about 6 h. Some simple analyses are further given for the other two events on 2 and 29 June 2013, in which the contributions of substorm injections and chorus waves are shown to be qualitatively comparable to those for the first event. These results clearly illustrate the respective importance of substorm injections and chorus waves for the evolution of radiation belt electrons at different energies on a relatively short timescale. Key Points Rapid outward extension of electron radiation belt observed by RBSP and THEMIS A two-step scenario to explain the rapid flux enchantment Differentiating between contributions of substorm injections and chorus waves

The trapping of equatorial magnetosonic waves in the Earth’s outer plasmasphere

Abstract We investigate the excitation and propagation of equatorial magnetosonic waves observed by the Van Allen Probes and describe evidence for a trapping mechanism for magnetosonic waves in the Earth\u27s plasmasphere. Intense equatorial magnetosonic waves were observed inside the plasmasphere in association with a pronounced proton ring distribution, which provides free energy for wave excitation. Instability analysis along the inbound orbit demonstrates that broadband magnetosonic waves can be excited over a localized spatial region near the plasmapause. The waves can subsequently propagate into the inner plasmasphere and remain trapped over a limited radial extent, consistent with the predictions of near-perpendicular propagation. By performing a similar analysis on another observed magnetosonic wave event, we demonstrate that magnetosonic waves can also be trapped within local density structures. We suggest that perpendicular wave propagation is important for explaining the presence of magnetosonic waves in the Earth\u27s plasmasphere at locations away from the generation region. Key Points Magnetosonic waves are excited by ion ring distributions near the plasmapauseMagnetosonic waves are trapped in a limited radial region in the plasmasphereMagnetosonic waves are modulated by local density structures

Nonlinear sub-cyclotron resonance as a formation mechanism for gaps in banded chorus

An interesting characteristic of magnetospheric chorus is the presence of a frequency gap at $\omega \simeq 0.5\Omega_e$, where $\Omega_e$ is the electron cyclotron angular frequency. Recent chorus observations sometimes show additional gaps near $0.3\Omega_e$ and $0.6\Omega_e$. Here we present a novel nonlinear mechanism for the formation of these gaps using Hamiltonian theory and test-particle simulations in a homogeneous, magnetized, collisionless plasma. We find that an oblique whistler wave with frequency at a fraction of the electron cyclotron frequency can resonate with electrons, leading to effective energy exchange between the wave and particles

Survey Analysis of Chorus Intensity at Saturn

In order to conduct theoretical studies or modeling of pitch angle scattering of electrons by whistler mode chorus emission at Saturn, a knowledge of chorus occurrence and magnetic intensity levels, PB, as well as the distribution of PB relative to frequency and spatial parameters is essential. In this paper an extensive survey of whistler mode magnetic intensity levels at Saturn is carried out, and Gaussian fits of PB are performed. We fit the spectrum of wave magnetic intensity between the lower hybrid frequency and fceq/2, and for frequencies in the interval fceq/2 < f <0.9 fceq, where fceq is the cyclotron frequency mapped to the equator. Saturn chorus is observed over most local times, but is dominant on the nightside in the range 4.5 < L <7.5, with minimum power at the equator and peak power in the range 5° < λ <10°. Saturn wave magnetic intensity averaged in frequency bins peaks in the range 10-5 < PB <10-4 nT2 for 0.4 < β <0.5 (β = f/fceq). Gaussian fits of PB with frequency and latitude are obtained for lower band chorus. Plasma injection regions are occasionally encountered with significant chorus power levels. Upper band chorus is seen almost exclusively within plasma injection regions, and the number of events is very limited, but when present, the average levels of PB can be higher than lower band chorus. The overall magnetic intensity contribution of the upper band, however, is insignificant relative to the lower band

ДИНАМІКА АКТИВНОСТІ ПРОЦЕСІВ ЛІПІДНОЇ ПЕРОКСИДАЦІЇ В СЕЛЕЗІНЦІ ПІД ВПЛИВОМ ГОСТРОЇ КРОВОВТРАТИ, УСКЛАДНЕНОЇ ІШЕМІЄЮ-РЕПЕРФУЗІЄЮ КІНЦІВКИ, ТА ЇЇ КОРЕКЦІЯ КАРБАЦЕТАМОМ

SUMMARY. The use of a tourniquet in conditions of massive external bleeding is the main means of rescuing wounded and injured in conditions of injuries of the main vessels of the extremities with a safe period of up to two hours. At the same time, it has been proven that two-hour complete ischemia-reperfusion of the limb causes activation of lipid peroxidation (LPO) processes in the internal organs, which in the conditions of acute blood loss contributes to the development of multiple organ failure. However, under conditions of acute blood loss complicated by ischemia-reperfusion of the limb, the intensity of LPO has not been studied in the spleen. The aim – to determine the effect of acute blood loss complicated by limb ischemia-reperfusion on the activity of LPO processes in the spleen and to evaluate the corrective efficacy of carbacetam. Material and Methods. 108 nonlinear male rats weighing 200–220 g were used in the experiments. All experiments were performed under thiopental-sodium anesthesia. In animals, limb ischemia-reperfusion and acute blood loss were simulated and these lesions were combined. In a separate group, the detected disorders were corrected with carbacetam. After 1 and 2 hours, as well as after 1, 7 and 14 days in the spleen of experimental animals, the content of diene conjugates (DC) and the content of reagents to thiobarbituric acid (TBA-active products of LPO) were determined. Results. It was established that under conditions of ischemia-reperfusion of the limb, acute blood loss and their combination there is an increase in lipid peroxidation in the spleen, which is manifested by an increase in the content of DC and TBA-active products of LPO. The general pattern of intensification of LPO in the spleen is to reach the maximum level in 1 day, followed by a decrease. An additional complication of acute blood loss by limb ischemia-reperfusion is accompanied by a significantly greater increase in the intensity of LPO in the spleen, compared with their individual simulation. Under the conditions of carbacetam correction in animals with acute blood loss complicated by ischemia-reperfusion of the limb, the activity of lipid peroxidation processes in the spleen decreased, which after 7 and 14 days was manifested by a significantly lower content of the studied LPO. Thus, carbacetam has a systemic antioxidant effect, which puts it in a number of promising ways to reduce the manifestations of oxidative disorders in the internal organs in conditions of acute blood loss complicated by ischemia-reperfusion of the limb, and prevention of poly-organ failure. Conclusions. Limb ischemia-reperfusion enhances lipid peroxidation processes in the spleen due to acute blood loss, accompanied by a statistically significant increase in DC content after 2 h and 14 days of the experiment and TBA-active LPO products – after 1, 7 and 14 days compared to animals, which simulated only acute blood loss. The use of carbacetam at a dose of 5 mg · kg-1 intraperitoneally has a pronounced antioxidant effect and after 7 and 14 days promotes less growth in the spleen of DC and TBA-active products of LPO.РЕЗЮМЕ. Применение турникета в условиях массивного наружного кровотечения является основным средством спасения раненых и пострадавших в результате ранений магистральных сосудов конечностей с безопасным сроком до двух часов. Одновременно доказано, что двухчасовая полная ишемия-реперфузия конечности вызывает активацию процессов пероксидного окисления липидов (ПОЛ) во внутренних органах, в условиях острой кровопотери способствует развитию полиорганной недостаточности. Однако в условиях острой кровопотери, осложненной ишемией-реперфузией конечности, интенсивность ПОЛ практически не исследована в селезенке. Цель – выяснить влияние острой кровопотери, осложненной ишемией-реперфузией конечности, на активность процессов ПОЛ в селезенке и оценить корректирующую эффективность карбацетама. Материал и методы. В экспериментах использовано 108 нелинейных крыс-самцов массой 200–220 г. Все эксперименты выполнены под тиопентал-натриевым наркозом. У животных моделировали ишемию-реперфузию конечности, острую кровопотерю и сочетали эти повреждения. В отдельной группе проводили коррекцию выявленных нарушений карбацетамом. Через 1 и 2 часа, а также через 1, 7 и 14 суток в селезенке подопытных животных определяли содержание диеновых конъюгатов (ДК) и реагентов к тиобарбитуровой кислоте (ТБК-активные продукты ПОЛ). Результаты. Установлено, что в условиях ишемии-реперфузии конечности, острой кровопотери и их сочетания имеет место усиление процессов липидной пероксидации в селезенке, что проявляется ростом содержания ДК и ТБК-активных продуктов ПОЛ. Общей закономерностью интенсификации ПОЛ в селезенке является достижение максимального уровня через 1 сутки с последующим снижением. Дополнительное осложнение острой кровопотери ишемией-реперфузией конечности сопровождается существенно большим ростом интенсивности ПОЛ в селезенке, по сравнению с их отдельным моделированием. В условиях коррекции карбацетамом у животных с острой кровопотерей, осложненной ишемией-реперфузией конечности, активность процессов липидной пероксидации в селезенке уменьшалась, что через 7 и 14 суток проявлялось существенно более низким содержанием исследуемых показателей ПОЛ. Итак, карбацетам проявляет системное антиоксидантное влияние, что ставит его в ряд перспективных средств снижения проявлений оксидативных нарушений во внутренних органах в условиях острой кровопотери, осложненной ишемией-реперфузией конечности, и профилактики развития полиорганной недостаточности. Выводы. Ишемия-реперфузии конечности способствует усилению процессов липидной перокисидации в селезенке, обусловленных острой кровопотерей, сопровождается статистически достоверно большим ростом содержания ДК через 2 часа и 14 суток эксперимента и ТБК-активных продуктов ПОЛ – через 1, 7 и 14 суток, по сравнению с животными, которым моделировали только острую кровопотерю. Применение карбацетама в дозе 5 мг·кг-1 внутрибрюшинно проявляет выраженное антиоксидантное влияние и через 7 и 14 суток способствует меньшему росту в селезенке ДК и ТБК-активных продуктов ПОЛ.РЕЗЮМЕ. Застосування турнікета за умов масивної зовнішньої кровотечі є основним засобом рятування поранених і постраждалих у результаті поранень магістральних судин кінцівок з безпечним терміном до двох годин. Одночасно доведено, що двогодинна повна ішемія-реперфузія кінцівки зумовлює активацію процесів пероксидного окиснення ліпідів (ПОЛ) у внутрішніх органах, що, за умов гострої крововтрати, сприяє розвитку поліорганної недостатності. Однак, за умов гострої крововтрати, ускладненої ішемією-реперфузією кінцівки, інтенсивність ПОЛ практично не досліджена в селезінці. Мета – з’ясувати вплив гострої крововтрати, ускладненої ішемією-реперфузією кінцівки, на активність процесів ПОЛ у селезінці та оцінити корегувальну ефективність карбацетаму. Матеріал і методи. В експериментах використано 108 нелінійних щурів-самців масою 200–220 г. Усі експерименти виконані під тіопентало-натрієвим наркозом. У тварин моделювали ішемію-реперфузію кінцівки, гостру крововтрату та поєднували ці ушкодження. В окремій групі проводили корекцію виявлених порушень карбацетамом. Через 1 і 2 години, а також через 1, 7 і 14 діб у селезінці піддослідних тварин визначали вміст дієнових кон’югатів (ДК) та вміст реагентів до тіобарбітурової кислоти (ТБК-активні продукти ПОЛ). Результати. Встановлено, що за умов ішемії-реперфузії кінцівки, гострої крововтрати та їх поєднання має місце посилення процесів ліпідної пероксидації в селезінці, що виявляється зростанням вмісту ДК та ТБК-активних продуктів ПОЛ. Загальною закономірністю інтенсифікації ПОЛ у селезінці є досягнення максимального рівня через 1&nbsp;добу з наступним зниженням. Додаткове ускладнення гострої крововтрати ішемією-реперфузією кінцівки супроводжується істотно більшим зростанням інтенсивності ПОЛ у селезінці, порівняно з їх окремим моделюванням. За умов корекції карбацетамом у тварин із гострою крововтратою, ускладненою ішемією-реперфузією кінцівки, активність процесів ліпідної пероксидації в селезінці зменшувалася, що через 7 і 14 діб проявлялося істотно нижчим вмістом досліджуваних показників ПОЛ. Отже, карбацетам чинить системний антиоксидантний вплив, що ставить його в ряд перспективних засобів зниження проявів оксидативних порушень у внутрішніх органах за умов гострої крововтрати, ускладненої ішемією-реперфузією кінцівки, та профілактики розвитку поліорганної недостатності. Висновки. Ішемія-реперфузія кінцівки сприяє посиленню процесів ліпідної пероксидації в селезінці, зумовлених гострою крововтратою, що супроводжується статистично вірогідно більшим зростанням вмісту ДК через 2 год і 14 діб експерименту та ТБК-активних продуктів ПОЛ – через 1, 7 і 14 діб, порівняно з тваринами, яким моделювали лише гостру крововтрату. Застосування карбацетаму в дозі 5 мг·кг-1 внутрішньоочеревинно чинить виражений антиоксидантний вплив і через 7 та 14 діб сприяє меншому зростанню в селезінці ДК та ТБК-активних продуктів ПОЛ