Congruent paleomagnetic and archeomagnetic records from the Western United States: a.d. 750 to 1450

Two independently dated, high-resolution paleomagnetic records, one lacustrine and one archeological, record the passage across western North America of the same nondipole feature of the geomagnetic field during the time interval from A.D. 750 to 1450. Although these sequences indicate that correlation between paleomagnetic and archeomagnetic records is feasible under certain conditions, differences between the records underscore the difficulty of dating accurately an archeological site by correlation of a single archeomagnetic direction with a secular variation curve.     

Pacific geomagnetic secular variation

We have considered several different types of records of long-period geomagnetic secular variation: direct measurements made in geomagnetic observatories; paleomagnetic measurements on Hawaiian lava flows with accurately known ages in the interval 0 to 200 years; paleomagentic measurements on Hawaiian lava flows with loosely determined ages within the interval 200 to 10,000 years ago; and worldwide paleomagnetic measurements of the average geomagnetic angular dispersion recorded in lava flows that formed during the past 0.7 million years. All these magnetic records indicate that, during this time, the nondipole component of the earth's field was lower in the central Pacific than elsewhere, as it is today. This, in turn, indicates that there is some type of inhomogeneity in the lower mantle which is coupled to the earth's core in such a way as to suppress the generation of the nondipole field beneath the central Pacific. With the present incomplete state of knowledge about the processes that give rise to the earth's field, it is uncertain whether undulations in the core-mantle interface or lateral variations in the composition and physical state of the lower mantle are ultimately responsible for the pattern of secular variation seen at the earth's surface.     

Paleomagnetic record of a geomagnetic field reversal from late miocene mafic intrusions, southern nevada

Late Miocene (about 8.65 million years ago) mafic intrusions and lava flows along with remagnetized host rocks from Paiute Ridge, southern Nevada, provide a high-quality paleomagnetic record of a geomagnetic field reversal. These rocks yield thermoremanent magnetizations with declinations of 227 degrees to 310 degrees and inclinations of -7 degrees to 49 degrees , defining a reasonably continuous virtual geomagnetic pole path over west-central Pacific longitudes. Conductive cooling estimates for the intrusions suggest that this field transition, and mafic magmatism, lasted only a few hundred years. Because this record comes principally from intrusive rocks, rather than sediments or lavas, it is important in demonstrating the longitudinal confinement of the geomagnetic field during a reversal.     

东北地区春玉米生育期内气候资源变化特征

为明确东北地区春玉米生育期内不同生育阶段气候资源的变化规律，基于东北地区40个农业气象试验站点的物候期观测记录及相应的气象站点逐日气象数据，对比分析了1981-1999年、2000-2016年春玉米营养生长期、并进期、生殖生长期和全生育期平均温度、生长度日、降水量、高温度日的时空变化特征。结果显示：①1981-2016年，东北地区春玉米全生育期及不同生育阶段的平均温度、生长度日和高温度日在空间分布上总体呈现相同的自东北向西南逐渐增加的趋势，降雨量呈现自西北向东南增加的趋势。②相比1981-1999年，2000-2016年春玉米全生育期及不同生育阶段的平均温度和生长度日总体呈现增加趋势，局部趋势不明显。降雨量在各生育期变化不明显，吉林省和辽宁省在并进期略有下降，黑龙江省在生殖生长期的降雨量减少。在营养生长期高温度日在空间上有增加趋势，特别是西部地区高温风险频率有较大增加。     

棉田与相邻荒漠过渡带蜘蛛群落结构及动态分析

对新疆莎车县棉田及相邻荒漠过渡带蜘蛛种类,群落结构及动态进行了初步的研究和分析.棉田及相邻荒漠过渡带的蜘蛛有13科、36属、39种.蜘蛛在两个不同生境群落特征及多样性有明显的差异性.逍遥蛛科和蟹蛛科为两个生境中共同的优势科.荒漠过渡带蜘蛛群落的物种数、个体数量、多样性、均匀度、稳定性都高于棉田蜘蛛群落的对应特征.荒漠过渡带蜘蛛群落结构的变动对棉田内蜘蛛群落的变化有明显的影响,可以初步肯定荒漠过渡带的种库作用.     

40Ar/39Ar Dating of the Brunhes-Matuyama Geomagnetic Field Reversal

Magnetostratigraphic studies are widely used in conjunction with the geomagnetic polarity time scale (GPTS) to date events in the range 0 to 5 million years ago. A critical tie point on the GPTS is the potassium-argon age of the most recent (Brunhes-Matuyama) geomagnetic field reversal. Astronomical values for the forcing frequencies observed in the oxygen isotope record in Ocean Drilling Project site 677 suggest that the age of this last reversal is 780 ka (thousand years ago), whereas the potassium-argon-based estimate is 730 ka. Results from 4039; Ar incremental heating studies on a series of lavas from Maui that straddle the Brunhes-Matuyama reversal give an age of 783 + 11 ka, in agreement with the astronomically derived value. The astronomically based technique appears to be a viable tool for dating young sedimentary sequences.     

Magnetic Damping of Rotation of the Vanguard I Satellite

Explicit integration of integrals of the type basic to comparison of observed and predicted values of the earth's mean total magnetic field reveals an error in the numerical integration recently employed by Raymond H. Wilson, Jr., in making such a comparison for the special case of Vanguard I. Correction of this error destroys the satisfactory agreement he found between the value implied by rotational damping and the theoretical value. Continued numerical improvement of all parts of my previous report, based on later accumulation and rediscussion of data, has revealed several small random adjustments, including the arithmetical correction discussed by LaPaz. The consequent result remains a satisfactory agreement of the groundobserved geomagnetic dipole field with that deduced from rotational retardation of the Vanguard I satellite.     

Effect of a near-zero magnetic field on development and flight of oriental armyworm(Mythimna separata)

The geomagnetic field affects all living organisms on the Earth. In this study we investigated the developmental and behavioral effects of rearing Mythimna separata in a near-zero magnetic field(500 n T) compared to the local geomagnetic field(approximately 50 μT). The near-zero magnetic field produced by a Helmholtz coil system significantly lengthened larval and pupal development durations, increased male longevity, and reduced pupal weight, female reproduction, and the relative expression level of the vitellogenin(Vg) gene in newly emerged females. Moreover, the near-zero magnetic field had a considerable negative effect on the mating ratio of M. separata adults. In addition, the moths in the near-zero magnetic field displayed less flight activity late in the night than those in the Earth's normal geomagnetic field, indicating that the flight rhythm of M. separata may be affected by the near-zero magnetic field. Reduction in magnetic field intensity may have negative effects on the development and flight of oriental armyworm, with consequent additional effects on its migration.     

Paleomagnetic field reversals and cosmic radiation

Faunal changes observed in association with reversals of the geomagnetic field have been attributed to increased radiation dosages produced by cosmic rays when the field intensity is greatly reduced. However, at currently observed cosmic ray and solar particle intensities, the additional dosages produced at sea level during a period of complete removal of the geomagnetic field are negligible. Furthermore, even complete dumping of the energetic particle in the radiation belts would not give rise to the necessary increased dosages.     

An episode of steep geomagnetic inclination 120,000 years ago

The mean inclinations of three sections of 120,000-year-old fine-grained sediments from northern California range from 62 degrees to 66 degrees . These inclinations are significantly steeper than the inclination of the geocentric axial dipole at this site. Because these sediments have probably recorded an actual episode of steep inclination lasting several thousand years, they provide new insights into the significance of mean inclinations shallower than the geocentric axial dipole. Such inclinations are characteristic of fine-grained sediments younger than 35,000 years. The results raise questions about the time-averaged geomagnetic field and about the determination of plate motions from paleomagnetic data.     

Magnetic direction finding: evidence for its use in migratory indigo buntings

The orientational capabilities of caged migratory indigo buntings were studied under differing magnetic field conditions. When tested in a situation allowing minimal exposure to visual cues but in the presence of the normal geomagnetic field, the birds demonstrated a significant orientation in the appropriate migratory direction (to the north). When the horizontal component of the magnetic field was deflected clockwise 120 degrees by activation of Helmholtz coils surrounding the cage, the orientation of the buntings shifted accordingly (clockwise to geographic east-southeast). These results suggest that indigo buntings are not only able to detect the geomagnetic field, but also can use this information in the finalization of their migratory direction.     

Magnetotactic bacteria at the geomagnetic equator

Magnetotactic bacteria are present in fresh water and marine sediments of Fortaleza, Brazil, situated close to the geomagnetic equator. Both South-seeking and North-seeking bacteria are present in roughly equal numbers in the same samples. This observation is consistent with the hypothesis that the vertical component of the geomagnetic field selects the predominant polarity type among magnetotactic bacteria in natural environments.     

Quantum spin hall insulator state in HgTe quantum wells

Recent theory predicted that the quantum spin Hall effect, a fundamentally new quantum state of matter that exists at zero external magnetic field, may be realized in HgTe/(Hg,Cd)Te quantum wells. We fabricated such sample structures with low density and high mobility in which we could tune, through an external gate voltage, the carrier conduction from n-type to p-type, passing through an insulating regime. For thin quantum wells with well width d < 6.3 nanometers, the insulating regime showed the conventional behavior of vanishingly small conductance at low temperature. However, for thicker quantum wells (d > 6.3 nanometers), the nominally insulating regime showed a plateau of residual conductance close to 2e(2)/h, where e is the electron charge and h is Planck's constant. The residual conductance was independent of the sample width, indicating that it is caused by edge states. Furthermore, the residual conductance was destroyed by a small external magnetic field. The quantum phase transition at the critical thickness, d = 6.3 nanometers, was also independently determined from the magnetic field-induced insulator-to-metal transition. These observations provide experimental evidence of the quantum spin Hall effect.     

秦岭豆科植物区系分析

在野外调查、标本鉴定以及文献资料查阅的基础上,运用植物区系地理学研究方法,对秦岭地区的豆科植物区系进行了分析。结果表明:1）秦岭地区共有豆科植物57属172种5亚种8变种,其中自然分布的种有44属144种5亚种6变种,生活型以草本和灌木为主,主要分布在海拔500～2 000 m的混交林带;2）该区的豆科植物区系成分复杂,具有较强的温带性质,含有温带属27属,占总属数的61.4%,温带分布种76种,占总种数的49.1%,中国特有种67种,占总种数的43.2%,中国特有种的分布类型体现了秦岭豆科植物区系与川滇地区的亲缘关系;3）秦岭豆科植物区系具有明显的过渡性,从秦岭南坡到北坡由亚热带性质向温带性质过渡,从秦岭西段到东段由中国—喜马拉雅植物成分向中国—日本植物成分过渡;4）通过与黄土高原、中国帕米尔高原、长白山、南岭及横断山区的豆科植物组成比较,发现秦岭豆科植物区系与黄土高原相似性最高,与帕米尔高原相似性最低。     

Local geomagnetic events associated with displacements on the san andreas fault

The piezomagnetic properties of rock suggest that a change in subsurface stress will manifest itself as a change in the magnetic susceptibility and remanent magnetization and hence the local geomagnetic field. A differential array of magnetometers has been operating since late 1965 on the San Andreas fault in the search for piezomagnetic signals under conditions involving active fault stress. Local changes in the geomagnetic field have been observed near Hollister, California, some tens of hours preceding the onset of abrupt creep displacement on the San Andreas fault.     

The paleomagnetic field from equatorial deep-sea sediments: axial symmetry and polarity asymmetry

Paleomagnetic data from 89 equatorial deep-sea sediment cores indicate that the configuration of the time-averaged geomagnetic field depends strongly on polarity state but that it remains within 1 degree of axial symmery throughout the Pliocene and Pleistocene (last 5 million years). The relative magnitude of the nondipole field was greater by almost a factor of 2 during reverse than during normal polarity intervals. These results thus support earlier suggestions that there may be a standing (nonreversing) component of the geomagnetic dynamo.     

Magnetic Anomalies over the Pacific-Antarctic Ridge

Four magnetic profiles across the Pacific-Antarctic Ridge reveal magnetic anomalies that show trends parallel with the ridge axis and symmetry about the ridge axis. The distribution of bodies that could cause these anomalies supports the Vine and Matthews hypothesis for the generation of patterns of magnetic anomalies associated with the midocean ridge system. The geometry of the bodies accords with the known reversals of the geomagnetic field during the last 3.4 million years, indicating a spreading rate of the ocean floor of 4.5 centimeters per year. If one assume that the spreading rate within 500 kilometers of the ridge axis has been constant, reversals of the geomagnetic field during the last 10.0 million years can be determined. This new, detailed history of field reversals accords with observed anomalies over Reykjanes Ridge in the North Atlantic if a spreading rate of 1 centimeter per year is assumed there.     

地磁场对广延大气簇射产生的次级带电粒子的偏转效应

用蒙特卡罗模拟的方法研究了在地磁场作用下,广延大气簇射产生的大量次级带电粒子所发生的偏转.研究发现,地磁场对从北方来的次级带电粒子的横向分布的影响比对从南方来的大,导致宇宙线观测阵列的触发效率南高于北,且随天顶角越大这种效应越明显.此外,用一次谐波和二次谐波对大量的模拟数据进行了拟合,给出了此种偏转效应对触发效率的影响程度.     

Geomagnetic Reversals during the Phanerozoic

An antalysis of worldwide paleomagnetic measurements suggests a periodicity of 350 x 10(6) years in the polarity of the geomagnetic field. During the Mesozoic it is predominantly normal, whereas during the Upper Paleozoic it is predominantly reversed. Although geomagnetic reversals occur at different rates throughout the Phanerozoic, there appeaars to be no clear correlation between biological evolutionary rates and reversal frequency.     

Dipolar antiferromagnetism and quantum criticality in LiErF₄

Magnetism has been predicted to occur in systems in which dipolar interactions dominate exchange. We present neutron scattering, specific heat, and magnetic susceptibility data for LiErF(4), establishing it as a model dipolar-coupled antiferromagnet with planar spin-anisotropy and a quantum phase transition in applied field H(c|| = 4.0 ± 0.1 kilo-oersteds. We discovered non-mean-field critical scaling for the classical phase transition at the antiferromagnetic transition temperature that is consistent with the two-dimensional XY/h(4) universality class; in accord with this, the quantum phase transition at H(c) exhibits three-dimensional classical behavior. The effective dimensional reduction may be a consequence of the intrinsic frustrated nature of the dipolar interaction, which strengthens the role of fluctuations.