Standstill Model Research Articles

Post-last glacial maximum expansion of Y-chromosome haplogroup C2a-L1373 in northern Asia and its implications for the origin of Native Americans.

Subbranches of Y-chromosome haplogroup C2a-L1373 are founding paternal lineages in northern Asia and Native American populations. Our objective was to investigate C2a-L1373 differentiation in northern Asia and its implications for Native American origins. Sequences of rare subbranches (n = 43) and ancient individuals (n = 37) of C2a-L1373 (including P39 and MPB373), were used to construct phylogenetic trees with age estimation by BEAST software. C2a-L1373 expanded rapidly approximately 17.7,000-14.3,000 years ago (kya) after the last glacial maximum (LGM), generating numerous sublineages which became founding paternal lineages of modern northern Asian and Native American populations (C2a-P39 and C2a-MPB373). The divergence pattern supports possible initiation of differentiation in low latitude regions of northern Asia and northward diffusion after the LGM. There is a substantial gap between the divergence times of C2a-MPB373 (approximately 22.4 or 17.7 kya) and C2a-P39 (approximately 14.3 kya), indicating two possible migration waves. We discussed the decreasing time interval of "Beringian standstill" (2.5 ky or smaller) and its reduced significance. We also discussed the multiple possibilities for the peopling of the Americas: the "Long-term Beringian standstill model," the "Short-term Beringian standstill model," and the "Multiple waves of migration model." Our results support the argument from ancient DNA analyses that the direct ancestor group of Native Americans is an admixture of "Ancient Northern Siberians" and Paleolithic communities from the Amur region, which appeared during the post-LGM era, rather than ancient populations in greater Beringia, or an adjacent region, before the LGM.

Terminal Pleistocene Alaskan genome reveals first founding population of Native Americans.

Despite broad agreement that the Americas were initially populated via Beringia, the land bridge that connected far northeast Asia with northwestern North America during the Pleistocene epoch, when and how the peopling of the Americas occurred remains unresolved. Analyses of human remains from Late Pleistocene Alaska are important to resolving the timing and dispersal of these populations. The remains of two infants were recovered at Upward Sun River (USR), and have been dated to around 11.5 thousand years ago (ka). Here, by sequencing the USR1 genome to an average coverage of approximately 17 times, we show that USR1 is most closely related to Native Americans, but falls basal to all previously sequenced contemporary and ancient Native Americans. As such, USR1 represents a distinct Ancient Beringian population. Using demographic modelling, we infer that the Ancient Beringian population and ancestors of other Native Americans descended from a single founding population that initially split from East Asians around 36 ± 1.5 ka, with gene flow persisting until around 25 ± 1.1 ka. Gene flow from ancient north Eurasians into all Native Americans took place 25-20 ka, with Ancient Beringians branching off around 22-18.1 ka. Our findings support a long-term genetic structure in ancestral Native Americans, consistent with the Beringian 'standstill model'. We show that the basal northern and southern Native American branches, to which all other Native Americans belong, diverged around 17.5-14.6 ka, and that this probably occurred south of the North American ice sheets. We also show that after 11.5 ka, some of the northern Native American populations received gene flow from a Siberian population most closely related to Koryaks, but not Palaeo-Eskimos, Inuits or Kets, and that Native American gene flow into Inuits was through northern and not southern Native American groups. Our findings further suggest that the far-northern North American presence of northern Native Americans is from a back migration that replaced or absorbed the initial founding population of Ancient Beringians.

Human Dispersal from Siberia to Beringia

With genetic studies showing unquestionable Asian origins of the first Americans, the Siberian and Beringian archaeological records are absolutely critical for understanding the initial dispersal of modern humans in the Western Hemisphere. The genetics-based Beringian Standstill Model posits a three-stage dispersal process and necessitates several expectations of the archaeological record of northeastern Asia. Here we present an overview of the Siberian and Beringian Upper Paleolithic records and discuss them in the context of a Beringian Standstill. We report that not every expectation of the model is met with archaeological data at hand.

Efficacy of Precordial Percussion Pacing Assessed in a Cardiac Standstill Microminipig Model.

Potential cardiovascular benefits of precordial percussion pacing (PPP) during cardiac standstill are unknown.Methods and Results:A cardiac standstill model in amicrominipigwas created by inducing complete atrioventricular block with a catheter ablation technique (n=7). Next, the efficacy of cardiopulmonary resuscitation by standard chest compressions (S-CPR), PPP and ventricular electrical pacing in this model were analyzed in series (n=4). To assess the mechanism of PPP, a non-selective, stretch-activated channel blocker, amiloride, was administered during PPP (n=3). Peak systolic and diastolic arterial pressures during S-CPR, PPP and ventricular electrical pacing were statistically similar. However, the duration of developed arterial pressure with PPP was comparable to that with ventricular electrical pacing, and significantly greater than that with S-CPR. Amiloride decreased the induction rate of ventricular electrical activity by PPP in a dose-related manner. Each animal survived without any neurological deficit at 24, 48 h and 1 week, even with up to 2 h of continuous PPP. In amicrominipigmodel of cardiac standstill, PPP can become a novel means to significantly improve physiological outcomes after cardiac standstill or symptomatic bradyarrhythmias in the absence of cardiac pacing. Activation of the non-selective stretch-activated channels may mediate some of the mechanophysiological effects of PPP. Further study of PPP by itself and together with S-CPR is warranted using cardiac arrest models of atrioventricular block and asystole.

Outside Beringia: Why the Northeast Asian Upper Paleolithic Record Does Not Support a Long Standstill Model

After nearly a century searching for evidence of Pleistocene Americans, in the last decade new methods, data, and ideas have brought us closer to reaching a clearer understanding of Native American...

Sinodonty, Sundadonty, and the Beringian Standstill model: Issues of timing and migrations into the New World

C.G. Turner II made dental morphological observations on thousands of Eskimo-Aleuts and American Indians and concluded they were derived from ancestral populations in northeast Asia during the last stages of the Pleistocene. He further distinguished two dental patterns in Asia. In East Asia, populations exhibit Sinodonty, a specialized dentition with intensified trait expressions. Southeast Asians exhibit Sundadonty, a more generalized dentition for crown and root traits. Turner argued all New World groups were derived from Sinodonts. Recent work has led some researchers to conclude there is evidence for the Sundadont pattern in Native American populations, an observation in accord with craniometric research that argues for an early migration of a generalized Asian population, followed by an influx of more specialized northeast Asians. A reanalysis of Turner's dataset fails to reveal evidence for a Sundadont component in the settlement of the Americas, but it does provide support for the Beringian Standstill model proposed by geneticists.

Two contemporaneous mitogenomes from terminal Pleistocene burials in eastern Beringia

Pleistocene residential sites with multiple contemporaneous human burials are extremely rare in the Americas. We report mitochondrial genomic variation in the first multiple mitochondrial genomes from a single prehistoric population: two infant burials (USR1 and USR2) from a common interment at the Upward Sun River Site in central Alaska dating to ∼11,500 cal B.P. Using a targeted capture method and next-generation sequencing, we determined that the USR1 infant possessed variants that define mitochondrial lineage C1b, whereas the USR2 genome falls at the root of lineage B2, allowing us to refine younger coalescence age estimates for these two clades. C1b and B2 are rare to absent in modern populations of northern North America. Documentation of these lineages at this location in the Late Pleistocene provides evidence for the extent of mitochondrial diversity in early Beringian populations, which supports the expectations of the Beringian Standstill Model.

Fundamental Electromagnetic Characteristics of Magnetically Anisotropic Damper-Wedges.

A magnetically anisotropic conductor was applied to the damper-wedge which acts as a slot wedge and damper bar in electrical rotating machinery. This conductor is composed of copper clad steel wires of 1.6mm diameter, which are aligned in the same radial direction. This means permeability in the direction of the wires, i.e. the thickness direction of the damper-wedge, is larger than the permeability perpendicular to this direction, and electrical conductivity is good. In order to evaluate the electromagnetic characteristics, a trial damper-wedge, 1.2m in length and with a steel space factor of 40% to total volume, was manufactured and mountained in a stand-still model iron core. Test results were as follows when the magnetically anisotropic damper-wedge was employed.(1) As the magnetic flux flowed well in the radial direction, the flux distribution at the core slot portion was flattened. Consequently, the ripple amplitude became small and the average flux density increased compared with cases when the non-magnetic or magnetic isotropic conductor are used.(2) The damper-wedge had a smaller skin effect for AC current than a conventional copper damper bar. The losses concentration for the damper system was relieved, so that better machine performance under heavy load condition would be obtained.

Fundamental electromagnetic characteristics of magnetically anisotropic damper‐wedges

AbstractA magnetically anisotropic conductor was applied to the damper‐wedge which acts as a slot wedge and damper bar in electrical rotating machinery. This conductor is composed of copper‐clad steel wires of 1.6 mm diameter aligned in the same radial direction. This means permeability in the direction of the wires, i.e., the thickness direction of the damper‐wedge, is larger than the permeability perpendicular to this direction, and electrical conductivity is good.To evaluate the electromagnetic characteristics, a trial damper‐wedge, 1.2 m in length and with a steel space factor of 40 percent to total volume, was manufactured and maintained in a standstill model iron core. Test results were as follows when the magnetically anisotropic damper‐wedge was employed.(1) As the magnetic flux flowed well in the radial direction, the flux distribution at the core slot portion was flattened. Consequently, the ripple amplitude became small and the average flux density increased compared with cases when the nonmagnetic or magnetic isotropic conductor is used.(2) The damper‐wedge had a smaller skin effect for ac current than a conventional copper damper bar. The losses concentration for the damper system was relieved so that better machine performance under heavy load condition would be obtained.