Postdoctoral Research Fellowship in Radiation Oncology Physics | University of California, San Diego
Males have better spatial skills, but stubbornness holds them back on a simple task.
A female guppy ponders her next move in a complex maze task.Image credits:
Friday, December 2, 2016 - 15:15
(Inside Science) -- Male fish are better than females at navigating a complex maze, but they flounder when faced with a simple transparent wall, according to a new study. The findings may indicate that females take a more flexible approach to solving problems, whereas males try to power through using sheer persistence.
"When the barrier was transparent, we found that females were much faster than males to perform the task," said Tyrone Lucon-Xiccato, a biologist at the University of Padua in Italy and first author of the study, which was published Nov. 19 in Animal Behaviour. "Males were getting stuck … persistently trying to pass through the barrier instead of detouring around it.”
The researchers hadn’t planned to test guppy persistence. Instead, they set out to test a well-established theory about how males and females evolve different spatial skills.
In monogamous species such as prairie voles, males and females live similar lifestyles, and they tend to be equally good at spatial tasks. But in most species, successful males mate with many females, and that means they have to travel.
"Males, in a way, are competing with each other spatially -- you know, who can patrol the largest home range and encounter the most females," said David Sherry, a behavioral neuroscientist at Western University in London, Ontario, who was not involved in the study. "You'd expect sexual selection to favor males who have good spatial ability."
The researchers set up two navigation tasks, one simple, and one complex. In the simple task (top), fish navigated around a transparent barrier to reach their goal -- a group of other fish that they wanted to join. In the complex task (bottom), the fish had to get past two walls, each of which had a real doorway and a doorway leading to a dead end.
Copyright American Institute of Physics (reprinting information)
In humans and many other mammal and bird species, males do tend to roam farther and have better spatial skills. To find out whether the same holds true in fish, the researchers turned to guppies, a species in which males mate with as many females as possible. Male guppies travel more than females, often moving to new pools in the river. They also spend more time close to shore, where there are plants and other landmarks to use for navigation. The researchers suspected that males' wide-ranging habits and complex environments would favor keen spatial skills. To test this prediction, they designed two navigation tasks -- one simple, and one complex -- and presented each task to 24 males and 24 females.
In the simple task, fish were presented with a clear plastic barrier, with short side walls to prevent them from slipping around by accident. The barrier let them see a group of other guppies, which the lonely fish wanted to join. When the transparent barrier was covered in mosquito netting to make it visible, males and females navigated the obstacle with equal ease. But when the barrier was completely clear, the average male spent nearly eight minutes just pushing against it, while the average female found her way around in under two minutes.
The researchers don't know why males struggled with the clear barrier, but they suspect it has more to do with persistence than spatial skills. They already knew that male guppies can be stubborn, thanks to a prior study in which guppies nudged aside one of two colored discs to find food. In that study, when the researchers switched which color concealed food, females were quicker to learn that the rules had changed. Similar studies in rats, chickens, and monkeys have also highlighted male persistence and female flexibility. The researchers speculate that persistence may help males overcome female reluctance to mate.
These ideas about persistence are plausible, said Sherry, and they call for further study. Enrique Font, an ethologist at the University of Valencia in Spain who was also not involved in the project, agrees.
"There might be some alternative explanations," he said. "They should perhaps try to do more experiments addressing that particular issue -- the difference in persistence between males and females."
While the simple task raised intriguing questions, the complex task gave answers, confirming predictions that males would do better in a difficult maze. In the complex task, guppies had to find their way past two barriers, each of which had a transparent panel and two doors. Males quickly learned which doors led to dead ends, and which led toward the other guppies visible through the window. More than 80 percent of males went straight for the correct doors on the second attempt. Females, in contrast, never learned the route, choosing doors at random in all five trials.
The results mark the first evidence of spatial skill differences between sexes in a fish, said Lucon-Xiccato. More importantly, they match results from other species, supporting the idea that each sex’s spatial ability reflects how much it travels. This, said Font, is the real strength of the study: By extending the pattern to a new group of animals, the researchers confirm that they understand how spatial skills evolve.Filed under
Authorized news sources may reproduce our content. Find out more about how that works. © 2016 American Institute of PhysicsAbout the Author Nala Rogers
Nala Rogers is a staff writer and editor at Inside Science, where she covers the Earth and Creature beats. She has a bachelor’s degree in biology from the University of Utah and a graduate certificate in science communication from U.C. Santa Cruz. Before joining Inside Science, she wrote for diverse outlets including Science, Nature, the San Jose Mercury News, and Scientific American. In her spare time she likes to explore wilderness.More by this author Creature
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Dispersed fluorescence spectroscopy of the SiCN Ã2Δ – X̃2Π system: Observation of some vibrational levels with chaotic characteristics
The laser induced fluorescence (LIF) spectrum of the Ã 2Δ – X̃ 2Π transition was obtained for SiCN generated by laser ablation under supersonic free jet expansion. The vibrational structures of the dispersed fluorescence (DF) spectra from single vibronic levels (SVL’s) were analyzed with consideration of the Renner-Teller (R-T) interaction. Analysis of the pure bending (ν 2) structure by a perturbation approach including R-T, anharmonicity, spin-orbit (SO), and Herzberg-Teller (H-T) interactions indicated considerably different spin splitting for the μ and κ levels of the X̃ 2Π state of SiCN, in contrast to identical spin splitting for general species derived from the perturbation approach, where μ and κ specify the lower and upper levels, respectively, separated by R-T. Further analysis of the vibrational structure including R-T, anharmonicity, SO, H-T, Fermi, and Sears interactions was carried out via a direct diagonalization procedure, where Sears resonance is a second-order interaction combined from SO and H-T interactions with Δ K = ± 1, ΔΣ = ∓1, and Δ P = 0, and where P is a quantum number, P = K + Σ. The later numerical analysis reproduced the observed structure, not only the pure ν 2 structure but also the combination structure of the ν 2 and the Si–CN stretching (ν 3) modes. As an example, the analysis demonstrates Sears resonance between vibronic levels, (0110) κ Σ(+) and (0200)μΠ12, with Δ K = ± 1 and Δ P = 0. On the basis of coefficients of their eigen vectors derived from the numerical analysis, it is interpreted as an almost one-to-one mixing between the two levels. The mixing coefficients of the two vibronic levels agree with those obtained from computational studies. The numerical analysis also indicates that some of the vibronic levels show chaotic characteristics in view of the two-dimensional harmonic oscillator (2D-HO) basis which is used as the basis function in the present numerical analysis; i.e., the eigen vectors for some of the observed levels have several components of the basis, and we have not been able to give precise vibronic assignments for the levels, but just vibronically labeled, referring the largest component in their vectors. (To emphasize this situation, we do not use the word “assignment,” but prefer to use “label” as the meaning of just “label,” but not “assign,” throughout this paper.) The latter shows that the vibronic labels of the levels are meaningless, and the P quantum number and the order of their eigen states in the P matrix block derived in the numerical analysis only characterize the vibronic levels. Comparing the constants obtained for all of the interactions with those of species showing Sears resonance and studied previously, it is found that none of them are strong, but are moderate. It is thus concluded that the chaotic appearance is not derived by any strong interaction, but is induced by complex and accidental proximities of the vibronic levels caused by the moderate interactions.
The surface interaction between substrates and block copolymers is one of the most important factors that control the alignment of self-assembled domains under thin film confinement. Most previous studies simply modeled substrates modified by grafting polymers as a hard wall with a specified surface energy, leading to an incomplete understanding of the role of grafted polymers. In this study, we propose a general model of surface interactions where the role of grafted polymers is decomposed into two independent contributions: the surface preference and the surface softness. Based on this model, we perform a numerical analysis of the stability competition between perpendicular and parallel lamellae of symmetric diblock copolymers on substrates modified by homopolymers using self-consistent field theory. The effects of the surface preference and the surface softness on the alignment of lamellar domains are carefully examined. A phase diagram of the alignment in the plane of the surface preference parameter and the surface softness parameter is constructed, which reveals a considerable parameter window for preparing stable perpendicular lamellae even on highly preferential substrates.
Vapor bridges between solid substrates in the presence of the contact line pinning effect: Stability and capillary force
In this work, we focus on investigating how nanobubbles mediate long-range interaction between neighboring solid substrates in the presence of the contact line pinning effect caused by surface heterogeneities. Using the constrained lattice density functional theory (LDFT), we prove that the nanobubbles, which take the form of vapor bridges here, are stabilized by the pinning effect if the separation between two substrates is less than a critical distance. The critical distance strongly depends on the chemical potential (i.e., the degree of saturation) and could become extremely long at a special chemical potential. Moreover, under the pinning effect, the substrate chemistry only determines the stability of the vapor bridges and the range of the capillary force, but has less influences on the magnitude of the capillary force, indicating that the substrate chemistry or the apparent contact angle for droplets or bubbles on the substrates is no longer a direct parameter to determine the magnitude of capillary force. A qualitative analysis for the two dimensional vapor bridges by considering the feedback mechanism can explain the results from the LDFT calculations.
We use molecular dynamics simulations to compare and contrast the liquid-state anomalies in the Stillinger-Weber models of monatomic water (mW), silicon (Si), and germanium (Ge) over a fairly wide range of temperatures and densities. The relationships between structure, entropy, and mobility, as well as the extent of the regions of anomalous behavior, are discussed as a function of the degree of tetrahedrality. We map out the cascade of density, structural, pair entropy, excess entropy, viscosity, and diffusivity anomalies for these three liquids. Among the three liquids studied here, only mW displays anomalies in the thermal conductivity, and this anomaly is evident only at very low temperatures. Diffusivity and viscosity, on the other hand, show pronounced anomalous regions for the three liquids. The temperature of maximum density of the three liquids shows re-entrant behavior consistent with either singularity-free or liquid-liquid critical point scenarios proposed to explain thermodynamic anomalies. The order-map, which shows the evolution of translational versus tetrahedral order in liquids, is different for Ge than for Si and mW. We find that although the monatomic water reproduces several thermodynamic and dynamic properties of rigid-body water models (e.g., SPC/E, TIP4P/2005), its sequence of anomalies follows, the same as Si and Ge, the silica-like hierarchy: the region of dynamic (diffusivity and viscosity) anomalies encloses the region of structural anomalies, which in turn encloses the region of density anomaly. The hierarchy of the anomalies based on excess entropy and Rosenfeld scaling, on the other hand, reverses the order of the structural and dynamic anomalies, i.e., predicts that the three Stillinger-Weber liquids follow a water-like hierarchy of anomalies. We investigate the scaling of diffusivity, viscosity, and thermal conductivity with the excess entropy of the liquid and find that for dynamical properties that present anomalies there is no universal scaling of the reduced property with excess entropy for the whole range of temperatures and densities. Instead, Rosenfeld’s scaling holds for all the three liquids at high densities and high temperatures, although deviations from simple exponential dependence are observed for diffusivity and viscosity at lower temperatures and intermediate densities. The slope of the scaling of transport properties obtained for Ge is comparable to that obtained for simple liquids, suggesting that this low tetrahedrality liquid, although it stabilizes a diamond crystal, is already close to simple liquid behavior for certain properties.
Bond dissociation energies of diatomic transition metal selenides: TiSe, ZrSe, HfSe, VSe, NbSe, and TaSe
Predissociation thresholds have been observed in the resonant two-photon ionization spectra of TiSe, ZrSe, HfSe, VSe, NbSe, and TaSe. It is argued that the sharp onset of predissociation corresponds to the bond dissociation energy in each of these molecules due to their high density of states as the ground separated atom limit is approached. The bond dissociation energies obtained are D0(TiSe) = 3.998(6) eV, D0(ZrSe) = 4.902(3) eV, D0(HfSe) = 5.154(4) eV, D0(VSe) = 3.884(3) eV, D0(NbSe) = 4.834(3) eV, and D0(TaSe) = 4.705(3) eV. Using these dissociation energies, the enthalpies of formation were found to be Δf,0KHo(TiSe(g)) = 320.6 ± 16.8 kJ mol−1, Δf,0KHo(ZrSe(g)) = 371.1 ± 8.5 kJ mol−1, Δf,0KHo(HfSe(g)) = 356.1 ± 6.5 kJ mol−1, Δf,0KHo(VSe(g)) = 372.9 ± 8.1 kJ mol−1, Δf,0KHo(NbSe(g)) = 498.9 ± 8.1 kJ mol−1, and Δf,0KHo(TaSe(g)) = 562.9 ± 1.5 kJ mol−1. Comparisons are made to previous work, when available. Also reported are calculated ground state electronic configurations and terms, dipole moments, vibrational frequencies, bond lengths, and bond dissociation energies for each molecule. A strong correlation of the measured bond dissociation energy with the radial expectation value, ⟨r⟩nd, for the metal atom is found.
We present an updated electron electric dipole moment (EDM) effective electric field of Eeff= 75.2 GV/cm and 229Th magnetic hyperfine interaction constant A || = −1266 MHz, the nucleon-electron scalar-pseudoscalar interaction constant W S = 106.0 kHz, and the molecule-frame static electric dipole moment D = −4.41 D for the Δ13 science state of ThO. The criticisms of the results from Fleig and Nayak [J. Mol. Spectrosc. 300, 16 (2014)] made in Skripnikov and Titov [J. Chem. Phys. 142, 024301 (2015)] are addressed and largely found to be unsubstantiated within the framework of the present approach. The present findings confirm the slightly relaxed constraints on relevant beyond-standard-model parameters, in particular the electron EDM, d e, and the nucleon-electron scalar-pseudoscalar coupling constant, C S.
Methane solids present more than one accessible crystalline phase at low temperature at zero pressure. We trap W(CO)6 in CH4 and CD4 matrices between 8 and 35 K to probe the interaction between an impurity and its surrounding molecular solid under various physical conditions. Linear and nonlinear vibrational spectroscopies of W(CO)6 highlight different kinds of interaction and reveal new and remarkable signatures of the phase transition of methane. The structures in the absorption band of the antisymmetric CO stretching mode exhibit a clear modification at the transition between phase II and phase I in CH4 and motional narrowing is observed upon temperature increase. The vibrational dynamics of this mode is probed in stimulated photon echo experiments performed with a femtosecond IR laser. A short component around 10 ps is detected in the population relaxation lifetime in the high temperature phase of solid CH4 (phase I) and disappears at lower temperatures (phase II) where the vibrational lifetime is in the hundreds of ps. The analysis of the nonlinear time-resolved results suggests that the short component comes from a fast energy transfer between the vibrational excitation of the guest and the lattice in specific families of sites. Such fast transfers are observed in the case of W(CO)6 trapped in CD4 because of an energy overlap of the excitation of W(CO)6 and a lattice vibron. In solid CH4, even when these V-V transfers are not efficient, pure dephasing processes due to the molecular nature of the host occur: they are temperature dependent without a clear modification at the phase transition.
We present a theoretical study of the Zeeman relaxation of the magnetically trappable lowest field seeking state of CrH(X6Σ+) in collisions with 3He. A two dimensional potential energy surface (PES) was calculated with the partially spin-restricted coupled cluster singles, doubles, and non-iterative triples [RCCSD(T)] method. The global minimum was found for the collinear He⋯Cr–H geometry with the well depth of 1143.84 cm−1 at R e = 4.15 a0. Since the RCCSD(T) calculations revealed a multireference character in the region of the global minimum, we performed additional calculations with the internally contracted multireference configuration interaction with the Davidson correction (ic-MRCISD+Q) method. The resulting PES is similar to the RCCSD(T) PES except for the region of the global minimum, where the well depth is 3032 cm−1 at R e = 3.8 a0. An insight into the character of the complex was gained by means of symmetry-adapted perturbation theory based on unrestricted Kohn-Sham description of the monomers. Close coupling calculations of the Zeeman relaxation show that although the ΔMJ=MJ′−MJ = −1 and −2 transitions are the dominant contributions to the collisional Zeeman relaxation, ΔMJ<−2 transitions cannot be neglected due to the large value of CrH spin-spin constant. The calculated elastic to inelastic cross section ratio is 1600 for the RCCSD(T) PES and 500 for the MRCISD+Q PES, while the estimate from the buffer-gas cooling and magnetic trapping experiment is 9000.
The combined effect of horizontal and vertical magnetic fields on the instability of the incompressible plasma layer of finite thickness through porous medium is investigated. The layer is confined between two rigid boundaries. The basic Magnetohydrodynamics set of equations have been constructed and linearized. The dispersion relation is obtained by applying the appropriate boundary conditions and solved numerically. The results show that the presence of both magnetic field components besides the resistive and convective terms will bring about more stability on the considered system.
Terahertz radiation generation and shape control by interaction of array Gaussian laser beams with plasma
In the present paper, a scheme for generation of terahertz (THz) radiation in electron-neutral collisional plasma based on beating of two Gaussian laser array beams has been proposed. It is shown that the efficiency of THz radiation based on the Gaussian laser array beams can be enhanced drastically in comparison with the efficiency of THz radiation based on the Gaussian one. Furthermore, the producing THz radiation by the Gaussian laser array beams, which has an exclusive field profile, is affected by some array structure parameters. It can also be used to overcome the negative consequences of electron neutral collisions in plasma, which may be occurring in the THz radiation generation process. Optimizing the collisional plasma, laser beams and array structure parameters, THz radiation efficiency up to 0.07% can be obtained in our scheme which is about three times greater than the maximum efficiency obtained for standard (single) Gaussian laser beam. Also, considering the electrostatic energy channel in solving the THz wave equation, and reduction of THz radiation efficiency to 0.054%, in this assumption, the ratio between the efficiency of Gaussian laser array beams and standard Gaussian laser beam remained unchanged.
We present two-dimensional hybrid kinetic/magnetohydrodynamic simulations of planned laser-ablation experiments in the Large Plasma Device. Our results, based on parameters that have been validated in previous experiments, show that a parallel collisionless shock can begin forming within the available space. Carbon-debris ions that stream along the magnetic-field direction with a blow-off speed of four times the Alfvén velocity excite strong magnetic fluctuations, eventually transferring part of their kinetic energy to the surrounding hydrogen ions. This acceleration and compression of the background plasma creates a shock front, which satisfies the Rankine–Hugoniot conditions and can therefore propagate on its own. Furthermore, we analyze the upstream turbulence and show that it is dominated by the right-hand resonant instability.
In this work, we have studied the interaction dynamics of the intense sub-cycle laser with the Xe2600 (Xenon) cluster by using a molecular dynamic code. The code is benchmarked against a couple of experimental works on Xe clusters. In the sub-cycle regime, the plane wave prescription of the laser pulse is not adequate, giving unrealistic field profiles, and hence in this study, we have relied on complex-source based sub-cycle pulsed beam model, which is an exact solution of Maxwell's equations. In order to see the effect of the sub-cycle pulses, the laser pulse duration is varied from 0.2 to 1 laser cycle while keeping the pulse energy conserved (by varying the peak amplitude with pulse duration). It has been observed that for the same laser energy the more energetic ions are obtained for sub-cycle pulses. Although the cluster explosion is symmetric, higher charge states are observed along the direction of laser polarization. The conversion efficiency of the energy absorbed per atom to average kinetic energy is found to be maximum for the shortest pulse duration of 0.2 laser cycle. The scaling law for maximum ion energy, total energy absorbed, and average kinetic energy of the ions with laser pulse duration is also deduced.
The effect of three different methods of adding O2 additive on O concentration of atmospheric pressure plasma jets (APPJs)
In order to maximize the O concentration generated by the atmospheric pressure plasma jets (APPJs), several different methods of adding O2 additive to working gas have been proposed. However, it is not clear, which method is capable of generating the highest concentration of O atom. In this paper, the concentration of O atoms in an APPJs by adding O2 to (1) the working gas, to (2) the downstream inside the tube, and (3) to the shielding gas is investigated by two-photon absorption laser-induced fluorescence spectrometry. The results clearly demonstrate that the highest O density is achieved when 1.5% of O2 is added to the working gas rather than the other two methods. In other words, the most effective way to generate O atoms is by premixing O2 with the working gas. Further investigation suggests that O atoms are mainly generated around the electrode region, where the electric field is highest. In addition, when O2 is added to the working gas, if in the meantime extra O2 is added to the downstream inside the tube, a significant decrease of O density is observed.