Individual variation in the pup attraction call produced by female Australian fur seals during early lactation

Otariid seals (fur seals and sea lions) are colonial breeders with large numbers of females giving birth on land during a synchronous breeding period. Once pups are born, females alternate between feeding their young ashore and foraging at sea. Upon return, both mother and pup must relocate each other and it is thought to be primarily facilitated by vocal recognition. Vocalizations of thirteen female Australian fur seals (Arctocephalus pusillus doriferus) were recorded during the breeding seasons of December 2000 and 2001, when pups are aged from newborns to one month. The pup attraction call was examined to determine whether females produce individually distinct calls which could be used by pups as a basis for vocal recognition. Potential for individual coding, discriminant function analysis (DFA), and classification and regression tree analysis were used to determine which call features were important in separating individuals. Using the results from all three analyses: F0, MIN F and DUR were considered important in separating individuals. In 76% of cases, the PAC was classified to the correct caller, using DFA, suggesting that there is sufficient stereotypy within individual calls, and sufficient variation between them, to enable vocal recognition by pups of this species.     

Field-induced quantum critical point in CeCoIn5

The resistivity of the heavy-fermion superconductor CeCoIn5 was measured as a function of temperature, down to 25 mK and in magnetic fields of up to 16 T applied perpendicular to the basal plane. With increasing field, we observe a suppression of the non-Fermi liquid behavior, rho approximately T, and the development of a Fermi liquid state, with its characteristic rho=rho(0)+AT2 dependence. The field dependence of the T2 coefficient shows critical behavior with an exponent of 1.37. This is evidence for a field-induced quantum critical point (QCP), occurring at a critical field which coincides, within experimental accuracy, with the superconducting critical field H(c2). We discuss the relation of this field-tuned QCP to a change in the magnetic state, seen as a change in magnetoresistance from positive to negative, at a crossover line that has a common border with the superconducting region below approximately 1 K.     

Hexagonal and square flux line lattices in CeCoIn5

Using small-angle neutron scattering, we have imaged the magnetic flux line lattice (FLL) in the d-wave heavy-fermion superconductor CeCoIn5. At low fields we find a hexagonal FLL. Around 0.6 T this undergoes what is most likely a first-order transition to square symmetry, with the nearest neighbors oriented along the gap node directions. This orientation of the square FLL is consistent with theoretical predictions based on the d-wave order parameter symmetry.     

Experimental evidence for anisotropic double-gap behavior in MgB2

The behavior of a type II superconductor in the presence of a magnetic field is governed by two characteristic length scales, the London penetration depth and the coherence length. We present magnetization measurements on MgB2 powder showing an anisotropy in the upper critical field and hence the coherence length of 6. Using the technique of small angle neutron scattering we show that this anisotropy is not mirrored in the London penetration depth, which is almost isotropic. This result can be explained by the superconductivity residing in two distinct electronic bands of the material, only one of which is highly anisotropic.     

Heat transport as a probe of electron scattering by spin fluctuations: the case of antiferromagnetic CeRhIn(5)

Heat and charge conduction were measured in the heavy-fermion metal CeRhIn(5), an antiferromagnet with T(N)=3.8 K. The thermal resistivity is found to be proportional to the magnetic entropy, revealing that spin fluctuations are as effective in scattering electrons as they are in disordering local moments. The electrical resistivity, governed by a q(2) weighting of fluctuations, increases monotonically with temperature. In contrast, the difference between thermal and electrical resistivities, characterized by a omega(2) weighting, peaks sharply at T(N) and eventually goes to zero at a temperature T(*) approximately = 8 K. T(*) thus emerges as a measure of the characteristic energy of magnetic fluctuations.     

From recursions to asymptotics: Durfee and dilogarithmic deductions

We consider two dimensional arrays p(n,k) which count a family of partitions of n by a second parameter k, usually the number of parts. Such arrays frequently satisfy a finite recursion of a certain form, detailed in formula (2), as well as an asymptotic relation

(∗)

For such situations, we can characterize (Theorem 1) the function g(u) in terms of a polynomial associated with the recursion. We also identify (Theorem 2) a class of families which satisfy both the desired recursion and the limit law (*). For such families, the function g(u) is characterized by Theorem 1, and this resolves a number of conjectures made in an earlier work [Electron. J. Combin. 5 (1998) R32] concerning asymptotic enumeration of partitions by the size of their Durfee square. Finally, we study a family of partitions introduced by Andrews [Amer. J. Math. 91 (1969) 18–24]. These partitions do satisfy the desired recursion, but it is not known for sure whether they also satisfy the accompanying limit law. We prove (Theorem 3), conditionally on the conjectured limit law holding, some identities involving the dilogarithm. These identities are seen empirically, by calculation to many decimal places, to be true.     

The asymptotic number of labeled graphs with given degree sequences

Asymptotics are obtained for the number of n × n symmetric non-negative integer matrices subject to the following constraints: (i) each row sum is specified and bounded, (ii) the entries are bounded, and (iii) a specified “sparse” set of entries must be zero. The result can be interpreted in terms of incidence matrices for labeled graphs.