Null Pairs Research Articles

Unraveling the consequences of the terminal Pleistocene megafauna extinction on mammal community assembly

Recent studies connecting the decline of large predators and consumers with the disintegration of ecosystems often overlook that this natural experiment already occurred. As recently as 14 ka, tens of millions of large‐bodied mammals were widespread across the American continents. Within 1000 yr of the arrival of humans, ∼ 80% were extinct including all > 600 kg. While the cause of the late Pleistocene (LP) extinction remains contentious, largely overlooked are the ecological consequences of the loss of millions of large‐bodied animals. Here, we examine the influence of the LP extinction on a local mammal community. Our study site is Hall's Cave in the Great Plains of Texas, which has unparalleled fine‐grained temporal resolution over the past 20 ka, allowing characterization of the community before and after the extinction. In step with continental patterns, this community lost 80% of large‐bodied herbivores and 20% of apex predators at the LP extinction. Using tightly constrained temporal windows spanning full glacial to modern time periods and comprehensive faunal lists, we reconstruct mammal associations and body size distributions over time. We find changes in alpha and beta diversity, and in the statistical moments associated with periods of climate change as well as with the LP extinction event. Additionally, there is a fundamental change in the composition of herbivores, with grazers being replaced by frugivores/granivores starting about 15 ka; the only large‐bodied grazer remaining today is the bisonBison bison. Moreover, the null model program PAIRS reveals interesting temporal patterns in the disassociation or co‐occurrence of species through the terminal Pleistocene and Holocene. Extinct species formed more significant associations than modern ones, and formed more aggregated pairs than do modern species. Further, negative species associations were about three times stronger than positive ones, suggesting that competitive interactions or environmental filtering are a strong force in community structure.

Abstract 1785: Chemical inhibition or transient knockdown of wild-type p53 induced phosphatase 1 (WIP1/PPM1D) potentiates the response to MDM2 inhibitors in a p53-dependent manner

Abstract The mechanisms that determine p53 cell fate decision after its non-genotoxic activation by MDM2 inhibitors are poorly understood. Wild-type p53-inducible phosphatase-1 (WIP1/PPM1D) forms an autoregulatory loop with p53 and is involved in the homeostasis of the p53 stress response network. WIP1 is activated, gained/amplified and overexpressed in a range of p53 wild-type malignancies. We investigated cellular growth/proliferation of p53 wild-type (wt) and matched p53 mutant (mut)/null cell line pairs, differing in WIP1 genetic status, in response to Nutlin-3 + GSK2830371 (WIP1i)/WIP1 siRNA-mediated knockdown. We also assessed the effects of WIP1i or knockdown in combination with Nutlin-3 on p53 post-translational modifications, p53 downstream transcriptional targets and apoptosis. Phosphorylation of p53S15 (pp53S15) was used as a marker of WIP1 catalytic activity. WIP1-amplified MCF-7p53wt cells were very sensitive to the WIP1i, with a 50% growth inhibitory concentration (GI50) of 2.65μM + 0.54 (SEM). The three p53 wild-type and mutant/null cell line pairs showed relatively little sensitivity to single agent WIP1i (GI50>10μM). However the WIP1i, at a non-growth inhibitory dose (2.5μM) in vitro, potentiated their response to Nutlin-3 in a p53-dependent manner. HCT116p53+/+; WIP1L450fs*1/+ (L450fs*1 is a WIP1 activating mutation), NGPp53wt and SJSA-1p53wt cell lines showed a 2.4-fold (p = 0.007), 2.1-fold (p = 0.04) and 1.3-fold (p = 0.02) decrease in their Nutlin-3 GI50 values respectively in the presence of WIP1i at 2.5μM. In contrast Nutlin-3 GI50 did not change in HCT116p53-/−, N20R1p53Mut and SN40R2p53Mut, NGP and SJSA-1 Nutlin-3 resistant daughter cell lines respectively. WIP1 transient siRNA knockdown also resulted in potentiation of cells to Nutlin-3. In WIP1-non-amplified (WNA) cells treated with either Nutlin-3 at the GI50 dose or 2.5μM WIP1i, pp53S15 was not detected, however in combination, these drugs resulted in dramatic levels of pp53S15. Interestingly protein expression of p53 targets MDM2 and p21 were not affected in WNA cells by the increased p53S15 phosphorylation; whereas BAX expression was elevated. The Nutlin-3 + WIP1i/siRNA knockdown combination also resulted in a significant increase in cell death markers between 24-48Hrs post-treatment in a p53-dependent manner. Although the strongest WIP1i potentiation of Nutlin-3 was observed in HCT116p53+/+; WIP1L450fs*1/+ cells which possess an activating WIP1 mutation, the NGPp53wt and SJSA-1p53wt cell lines with wild-type WIP1 also showed potentiation. These findings highlight the mechanistic importance of the p53-WIP1 autoregulatory loop in cell fate determination after non-genotoxic p53 activation by Nutlin-3. Potent inhibitors of WIP1 may potentiate the response to other therapeutics aiming to activate p53 mediated tumour suppression. Citation Format: Arman Esfandiari, Nicola J. Curtin, John Lunec. Chemical inhibition or transient knockdown of wild-type p53 induced phosphatase 1 (WIP1/PPM1D) potentiates the response to MDM2 inhibitors in a p53-dependent manner. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1785. doi:10.1158/1538-7445.AM2015-1785

ENERGY DISSIPATION IN MAGNETIC NULL POINTS AT KINETIC SCALES

We use kinetic particle-in-cell and magnetohydrodynamic simulations supported by an observational dataset to investigate magnetic reconnection in clusters of null points in space plasma. The magnetic configuration under investigation is driven by fast adiabatic flux rope compression that dissipates almost half of the initial magnetic field energy. In this phase powerful currents are excited producing secondary instabilities, and the system is brought into a state of `intermittent turbulence' within a few ion gyro-periods. Reconnection events are distributed all over the simulation domain and energy dissipation is rather volume-filling. Numerous spiral null points interconnected via their spines form null lines embedded into magnetic flux ropes; null point pairs demonstrate the signatures of torsional spine reconnection. However, energy dissipation mainly happens in the shear layers formed by adjacent flux ropes with oppositely directed currents. In these regions radial null pairs are spontaneously emerging and vanishing, associated with electron streams and small-scale current sheets. The number of spiral nulls in the simulation outweighs the number of radial nulls by a factor of 5\---10, in accordance with Cluster observations in the Earth's magnetosheath. Twisted magnetic fields with embedded spiral null points might indicate the regions of major energy dissipation for future space missions such as Magnetospheric Multiscale Mission (MMS).

How to find magnetic nulls and reconstruct field topology with MMS data?

AbstractIn this study, we apply a new method—the first‐order Taylor expansion (FOTE)—to find magnetic nulls and reconstruct magnetic field topology, in order to use it with the data from the forthcoming MMS mission. We compare this method with the previously used Poincare index (PI), and find that they are generally consistent, except that the PI method can only find a null inside the spacecraft (SC) tetrahedron, while the FOTE method can find a null both inside and outside the tetrahedron and also deduce its drift velocity. In addition, the FOTE method can (1) avoid limitations of the PI method such as data resolution, instrument uncertainty (Bz offset), and SC separation; (2) identify 3‐D null types (A, B, As, and Bs) and determine whether these types can degenerate into 2‐D (X and O); (3) reconstruct the magnetic field topology. We quantitatively test the accuracy of FOTE in positioning magnetic nulls and reconstructing field topology by using the data from 3‐D kinetic simulations. The influences of SC separation (0.05~1 di) and null‐SC distance (0~1 di) on the accuracy are both considered. We find that (1) for an isolated null, the method is accurate when the SC separation is smaller than 1 di, and the null‐SC distance is smaller than 0.25~0.5 di; (2) for a null pair, the accuracy is same as in the isolated‐null situation, except at the separator line, where the field is nonlinear. We define a parameter ξ ≡ |( λ1 + λ2 + λ3 )|/|λ|max in terms of the eigenvalues (λi) of the null to quantify the quality of our method—the smaller this parameter the better the results. Comparing to the previously used parameter (η≡|∇ ⋅ B|/|∇ × B|), ξ is more relevant for null identification. Using the new method, we reconstruct the magnetic field topology around a radial‐type null and a spiral‐type null, and find that the topologies are well consistent with those predicted in theory. We therefore suggest using this method to find magnetic nulls and reconstruct field topology with four‐point measurements, particularly from Cluster and the forthcoming MMS mission. For the MMS mission, this null‐finding algorithm can be used to trigger its burst‐mode measurements.

The Lexicon–Syntax Interface: Root Semantics As An Indirect Determinant Of Intransitive Verb Syntax In Cree

This paper presents a study of the (Northern East) Cree intransitive verb final (verbalizing suffix) -piyi ‘move’, which occurs in eventive unaccusatives and in two classes of unergative: vehicular motion verbs and verbs of emission. Generally, Algonquian intransitive finals systematically correlate with an external argument, or an internal argument, but not with both. We argue that -piyi is no exception, correlating with an internal (theme) argument. A null verb final, which correlates with an external argument (an internal causer), derives the unergatives, in which cases -piyi is lexicalized into a complex root. Root semantics are an indirect predictor of verb type in that they reflect patterns of legitimate pairing with either -piyi or the null final; e.g., -piyi pairs with root[STATE] to yield an unaccusative, while the null final pairs with the lexicalized root [root[PATH]+piyi] to yield an unergative. This analysis is compatible with a little-v analysis of finals (among others, Ritter and Rosen 2010). The unaccusatives have a spontaneous occurrence reading which, following Davis and Demirdache (2000), we attribute to -piyi suppressing the “causing process” sub-event in a causative representation. Our analysis is thus compatible with the view that some, if not all, unaccusatives are semantically causative (among others, Levin and Rappaport Hovav 1995).

Boosted Surfaces: Synthesis of Meshes using Point Pair Generators as Curvature Operators in the 3D Conformal Model

This paper introduces a new technique for the formulation of parametric surfaces. Applying translation operations to tangent vectors $${n_{\circ} {\bf \upsilon}}$$ results in null point pairs $${\tau}$$ . We treat these null point pairs as surface and mesh curvature control points which can be interpolated and exponentiated to construct continuous topological transformations $${\mathcal{K}}$$ of the form $${e^{{-}\frac{\tau}{2}}}$$ 2. Some basic algorithms are proposed, including the boost which bends a line to a circle of curvature $${\kappa}$$ , and the twisted boost which generates the Hopf fibration. We investigate methods to control curvature in two orthogonal directions u and v and examine a few distance-based and linear weighting techniques for synthesizing surface patches using multiple curvature control points. We consider the expressivity of the technique in manipulating meshes, and find that applying these rotors to mesh points provides a novel and computationally efficient method for creating boosted forms.

Current structure and nonideal behavior at magnetic null points in the turbulent magnetosheath

The Poincaré index indicates that the Cluster spacecraft tetrahedron entraps a number of 3‐D magnetic nulls during an encounter with the turbulent magnetosheath. Previous researchers have found evidence for reconnection at one of the many filamentary current layers observed by Cluster in this region. We find that many of the entrained nulls are also associated with strong currents. We dissect the current structure of a pair of spiral nulls that may be topologically connected. At both nulls, we find a strong current along the spine, accompanied by a somewhat more modest current perpendicular to the spine that tilts the fan toward the axis of the spine. The current along the fan is comparable to the that along the spine. At least one of the nulls manifests a rotational flow pattern in the fan plane that is consistent with torsional spine reconnection as predicted by theory. These results emphasize the importance of examining the magnetic topology in interpreting the nature of currents and reconnection in 3‐D turbulence.

Electron acceleration by whistler-mode waves around the magnetic null during 3D reconnection

The magnetic field configuration around a magnetic null pair and its associated electron behavior during 3D magnetic reconnection have recently been reported from in situ observations. Electrons are suggested to be temporarily trapped in the central reconnection region as indicated by an electron density peak observed near the magnetic null (He J-S et al 2008 Geophys. Res. Lett. 35 L14104). It is highly interesting that energetic electron beams of a few kiloelectronvolts are found to be related to the magnetic null structure. However, the acceleration mechanism is still not fully understood. In this paper, we show that strong whistler-mode electromagnetic waves are indeed found around the magnetic null. Further we propose a new electron acceleration scenario of trapped electrons near the magnetic null points driven by the whistler-mode waves, which is confirmed by numerical results. It is demonstrated that whistler waves can enhance the phase space density (PSD) of electrons for energies of ∼2 keV by a factor of 100 at lower pitch angles very rapidly, typically within 2 s. The accelerated electrons may escape from the loss cone of the magnetic cusp mirrors around the magnetic null, leading to the observed energetic beams.

Dynamics and waves near multiple magnetic null points in reconnection diffusion region

Identifying the magnetic structure in the region where the magnetic field lines break and how reconnection happens is crucial to improving our understanding of three‐dimensional reconnection. Here we show the in situ observation of magnetic null structures in the diffusion region, the dynamics, and the associated waves. Possible spiral null pair has been identified near the diffusion region. There is a close relation among the null points, the bipolar signature of the Z component of the magnetic field, and enhancement of the flux of energetic electrons up to 100 keV. Near the null structures, whistler‐mode waves were identified by both the polarity and the power law of the spectrum of electric and magnetic fields. It is found that the angle between the fans of the nulls is quite close to the theoretically estimated maximum value of the group‐velocity cone angle for the whistler wave regime of reconnection.

Observation of the lower hybrid waves near the three-dimensional null pair

Magnetic reconnection is a fundamental process in plasma, which is thought to play important roles both in laboratory and natural plasmas through affecting magnetic topology, heating and accelerating particles. During an event on Oct. 1st, 2001, the Cluster tetrahedron circled around the magnetic reconnection region several times, and Xiao et al. first identified the null pair and found that the spectrum of the null-point oscillation shows the maximum power near the lower-hybrid frequency. In this paper we report the observation of electromagnetic and electrostatic wave enhancements near lower hybrid frequency associated with the reconnection process near the null pair. The lower hybrid waves (LHWs) with quasi-perpendicular propagation were identified and also confirmed by the power law of the spectrum of electric and magnetic fields.

Electron trapping around a magnetic null

Magnetic reconnection is an important process in astrophysical, space and laboratory plasmas. The magnetic null pair structure is theoretically suggested to be a crucial feature of the three‐dimensional magnetic reconnection. The physics around the null pair, however, has not been explored in combination with the magnetic field configuration deduced from in situ observations. Here, we report the identification of the configuration around a null pair and simultaneous electron dynamics near one null of the pair, observed by four Cluster spacecraft in the geo‐magnetotail. Further, we propose a new scenario of electron dynamics in the null region, suggesting that electrons are temporarily trapped in the central reconnection region including electron diffusion region resulting in an electron density peak, accelerated possibly by parallel electric field and electron pressure gradient, and reflected from the magnetic cusp mirrors leading to the bi‐directional energetic electron beams, which excite the observed high frequency electrostatic waves.

Satellite observations of separator-line geometry of three-dimensional magnetic reconnection

Detection of a separator line that connects magnetic nulls and the determination of the dynamics and plasma environment of such a structure can improve our understanding of the three-dimensional (3D) magnetic reconnection process1,2,3,4,5,6,7,8,9. However, this type of field and particle configuration has not been directly observed in space plasmas. Here we report the identification of a pair of nulls, the null–null line that connects them, and associated fans and spines in the magnetotail of the Earth using data from the four Cluster spacecraft. With di and de designating the ion and electron inertial lengths, respectively, the separation between the nulls is found to be ∼0.7±0.3di and an associated oscillation is identified as a lower-hybrid wave with wavelength ∼de. This in situ evidence of the full 3D reconnection geometry and associated dynamics provides an important step towards establishing an observational framework of 3D reconnection.

Multiply Connected Source and Null Pairs

The magnetic fields within the solar atmosphere have a complex topology owing to the fragmentary nature with which they thread the solar surface. The topologies of the potential magnetic fields containing only a few (up to four) point photospheric sources have been classified. For small numbers of sources determining the connectivity of source pairs is equivalent to counting the number of flux domains. As the numbers of sources increase this, however, is no longer the case. Instead, a pair of connected sources can have more than one distinct flux domain linking them. We call these multiply connected source pairs. Pairs of nulls connected by more than one separator are called multiply connected null pairs. Multiply connected source and null pairs go hand-in-hand such that two separators connecting the same pair of nulls immediately implies multiple flux domains linking the same source pair and vice versa. It is found that multiply connected source pairs are common not only in fairly complex potential magnetic fields but more interestingly in the resistive-MHD evolution of both simple and complex magnetic fields. Magnetic energy release is often significant around separators. Thus fields with multiply connected source pairs, which naturally have more separators, (i) have more sites for intense energy release and (ii) are likely to release energy more quickly than other magnetic fields. Moreover, the combination of multiply connected source and null pairs can give rise to a situation where flux is reconnected repeatedly between two flux domains.

Local realizations and local polynomial matrix representations of systems

We define the local polynomial matrix representations of a controllable matrix pair ( A, B) with elements in an arbitrary field F and the local realizations of a nonsingular polynomial matrix whose elements are in F [ s ] with respect to a nonempty subset of Specm ( F [ s ] ) . We give different characterizations of these local concepts. In particular, when F = C , local realizations and left null pairs as defined in Gohberg et al. [I. Gohberg, M.A. Kaashoek, F. van Schagen, Partially Specified Matrices and Operators: Classification, Completion, Applications, Bikhäuser, Basel, 1995] are closely related. Moreover, global polynomial matrix representations and global realizations, as defined in Zaballa [I. Zaballa, Controllability and hermite indices of matrix pairs, Int. J. Control 68 (1) (1997) 61–86] are particular cases of the same local concepts. Finally, local Wiener–Hopf factorization indices with respect to a nonempty subset of Specm ( F [ s ] ) are defined.

Orthographic neighborhood size effects in recognition memory

This study argues for the importance of physical word features in recognition memory by investigating the influence of orthographic distinctiveness. Experiment 1 demonstrated a mirror effect in ayes/no recognition test by manipulating orthographic neighborhood size. Words with small neighborhoods showed more hits and fewer false alarms than did words with larger neighborhoods. Experiment 2 replicated the neighborhood size mirror effect using null pairs in a forced choice recognition test. Experiment 3 required remember/know judgments in a yes/no recognition task. Experiment 4 used the same yes/no test as did Experiment 1, adding a study task that drew attention away from orthographic information in the study list. The mirror pattern disappeared with the addition of the study task.

Dynamic Three‐dimensional Reconnection in a Separator Geometry with Two Null Points

The dynamic behavior of disturbances in the vicinity of a pair of magnetically connected three-dimensional null points is examined. The aim is to investigate how nonlinear disturbances lead to strong localized currents that initiate magnetic reconnection at the separator. The problem is formulated in an incompressible cylindrical geometry by superposing arbitrary disturbance fields onto a two-null field. Two different regimes are found for the dynamic evolution, depending on the relative strengths of the background magnetic and velocity fields. In one regime, disturbance pulses split into ingoing and outgoing components, which propagate along the background field lines. In the other flux pileup regime, a strong driving flow localizes the disturbances toward the null point pair. Current structures aligned with the spines, fans, and separator present in the field are found to result, and the structure of these currents and their scaling with resistivity is investigated.

Searching for epistatic interactions in nuclear families using conditional linkage analysis

BackgroundGenomic screens generally employ a single-locus strategy for linkage analysis, but this may have low power in the presence of epistasis. Ordered subsets analysis (OSA) is a method for conditional linkage analysis using continuous covariates.MethodsWe used OSA to evaluate two-locus interactions in the simulated Genetic Analysis Workshop 14 dataset. We used all nuclear families ascertained by Aipotu, Karangar, and Danacaa. Using the single-nucleotide polymorphism map, multipoint affected-sibling-pair (ASP) linkage analysis was performed on all 100 replicates for each chromosome using SIBLINK. OSA was used to examine linkage on each chromosome using LOD scores at each 3-cM location on every other chromosome as covariates. Two methods were used to identify positive results: one searching across the entire covariate chromosome, the other conditioning on location of known disease loci.ResultsSingle-locus linkage analysis revealed very high LOD scores for disease loci D1 through D4, with mean LOD scores over 100 replicates ranging from 4.0 to 7.8. Although OSA did not obscure this linkage evidence, it did not detect the simulated interactions between any of the locus pairs. We found inflated type I error rates using the first OSA method, highlighting the need to correct for multiple comparisons. Therefore, using "null chromosome pairs" without simulated disease loci, we calculated a corrected alpha-level.ConclusionWe were unable to detect two-locus interactions using OSA. This may have been due to lack of incorporation of phenotypic subgroups, or because linkage evidence as summarized by LOD scores performs poorly as an OSA covariate. We found inflated type I error rates, but were able to calculate a corrected alpha-level for future analyses employing this strategy to search for two-locus interactions.

MHD wave propagation in the neighbourhood of two null points

The nature of fast magnetoacoustic and Alfven waves is investigated in a zero β plasma in the neighbourhood of a pair of two-dimensional null points. This gives an indication of wave propagation in the low β solar corona, for a more complicated magnetic configuration than that looked at by McLaughlin & Hood (2004, A&A, 420, 1129). It is found that the fast wave is attracted to the null points and that the front of the wave slows down as it approaches the null point pair. Here, the wave splits and part of the wave accumulates at one null and the rest at the other. Current density will then accumulate at these points and ohmic dissipation will then extract the energy in the wave at these points. This suggests locations where wave heating will occur in the corona. The Alfven wave behaves in a different manner in that the wave accumulates along the separatrices. Hence, the current density will accumulate at this part of the topology and this is where wave heating will occur. However, the phenomenon of wave accumulation at a specific place is a feature of both wave types, and illustrates the importance of studying the topology of the corona when considering MHD wave propagation.

Null systems and sequence entropy pairs

A measure-preserving transformation (respectively a topological system) is null if the metric (respectively topological) sequence entropy is zero for any sequence. Kushnirenko has shown that an ergodic measure-preserving transformation has a discrete spectrum if and only if it is null. We prove that for a minimal system this statement remains true modulo an almost one-to-one extension. It allows us to show that a scattering system is disjoint from any null minimal system. Moreover, some necessary conditions for a transitive non-minimal system to be null are obtained.Localizing the notion of sequence entropy, we define sequence entropy pairs and show that there is a maximal null factor for any system. Meanwhile, we define a weaker notion, namely weak mixing pairs. It turns out that a system is weakly mixing if and only if any pair not in the diagonal is a sequence entropy pair if and only if the same holds for a weak mixing pair, answering a question in Blanchard et al (F. Blanchard, B. Host and A. Maass, Topological complexity. Ergod. Th. & Dynam. Sys., 20 (2000), 641–662). For a group action we give a direct proof of the fact that the factor induced by the smallest invariant equivalence relation containing the regionally proximal relation is equicontinuous. Furthermore, we show that a non-equicontinuous minimal distal system is not null.

Almost Kählerian manifolds of hyperbolic type

We study the geometry of completely real submanifolds of almost Kählerian manifolds of hyperbolic type. The main aim is the study of the geometry of the manifold of non-degenerate null pairs of the real projective space. We obtain a complete classification of its totally geodesic Lagrangian submanifolds and describe their construction.