David Gray

An Extremely Low Equivalent Magnetic Noise Magnetoelectric Sensor

As a result of the coupling between their dual order parameters, multiferroic materials exhibit unusual physical properties and, in turn, promise new device applications. [ 1 , 2 ] Of particular interest is the existence of a cross-coupling between the magnetic and electric orders, termed the magnetoelectric (ME) effect. [ 3–5 ] Because no single-phase material has been put forward demonstrating a practical capacity for such coupling at room temperature, [ 8 ] many of the most promising applications offered by the ME effect, including magnetic fi eld sensors and electric write-magnetic read memory devices, have not been forthcoming. [ 6 , 7 ] Furthermore, the exploitation of high magnetic fi eld sensitivity in two-phase ferromagnetic/ferroelectric composites requires development and identifi cation of end users. [ 7 ]

Crenulation cleavage differentiation: implications of solution-deposition processes

Abstract Metamorphic differentiation associated with cleavage development in crenulated anisotropic rock fabrics is commonly due to a redistribution of mineral phases within a certain volume of the fabric. Such a volume redistribution can be explained by solution transfer of soluble minerals from sites of high chemical potential, fold limbs, to sites of low chemical potential, fold hinges. The processes involved are dissolution, diffusional transfer via grain-boundaries and redeposition. The driving force for the diffusion, differences in chemical potential, is relatable to stress and fabric variations around the microfolds. The rate of transfer is influenced by the initial solubility of the mineral grains, the kinetics of grain-boundary diffusion, the nature of grain contacts and the microfold wavelength. The sense of migration of dissolved species is dependent on spatial variations in the magnitudes of normal stress and mean stress combined with grain shape and grain orientation changes around the microfolds.

Investigations on the mechanical significance of crenulation cleavage

Abstract Measurements of total, incremental and progressive strains associated with the development of small scale crenulation cleavage in some low-grade metamorphic rocks from Australia and Switzerland are applied to a discussion of the mechanical significance of the cleavage. Limits are placed on the amount of incremental and total slip or simple shear possible along the cleavage by the observation that the XY principal plane trace of bulk total crenulation strain coincides within 4° of the crenulation cleavage trace in all cases where this strain has been measured or estimated. The measurements are made on eight specimens using deformed porphyroblasts, crystal fibres in pressure-shadows around pyrite and flattened folds and include deformations with coaxial and non-coaxial histories. Further measurements derived from pressure-shadow fibres (eight specimens) show that the style and orientation of incremental deformation are essentially independent of the crenulation cleavage, except for a limit (43°) to the obliquity of the principal incremental extension axis during a given cleavage episode. The only special deformation related to the cleavage is the coaxial one. An indication of passive cleavage behaviour at high strain is shown by the progressive strain history of one specimen. Evidence for passive rotation of a transected axial plane is shown by another. A model is proposed to account for these observations, especially the conditions necessary for initiation and continued development of a new cleavage fabric. Some further applications of existing strain measurement techniques are described: of the Rf/Of method to heterogeneously superposed tectonic strains and of an improved procedure of t′α/α flattening analysis.

Cleavage-fold relationships and their implications for transected folds: an example from southwest Virginia, U.S.A.

Abstract A non-coaxial deformation involving pre-folding initiation of cleavage perpendicular to bedding is proposed to explain non-axial planar cleavage associated with mesoscopic folds in part of the Appalachian foreland thrust-belt of southwest Virginia. Folds are gently plunging, asymmetric, upright to slightly inclined, sinusoidal forms with non-axial fanning cleavage. They show extreme local variations in type and degree of transection and the consistency of transection direction. These relations are further complicated by hinge migration. Cleavage-fan angles, bedding-cleavage angles and δ transection values appear influenced by fold tightness, and in part by fold flattening strain. Fold flattening increments are considered simultaneous with folding. Axial surface traces, and not cleavage traces, coincide with the principal extension direction in fold profiles. Geometric modelling of cleavage fanning and bedding-cleavage angle variations for various theoretical folding modes suggest that folding in limestone and sandstone layers was by tangential longitudinal strain. Significant shape modification and change in bedding-cleavage relations occurred after limb dips of 40 and 50° were attained in limestone and sandstone respectively. Mud-rock class 1C folds with convergent cleavage fans show features transitional between buckling and flexural flow. Initiation of ‘cleavage’ fabrics during layer-parallel shortening prior to significant folding may be important for cleavage evolution in some deformed rocks.

Pencil structure and strain in weakly deformed mudstone and siltstone

Abstract Weakly deformed mudstone and siltstone (Middle Ordovician Knobs Formation) of the Appalachian Valley and Ridge Province, south-western Virginia, U.S.A. show strain-dependent transitions between bedding fissility, pencil structure and cleavage. Pencil structures are associated with a bulk inhomogeneous shortening deformation where minimum principal strain ( Z ) ranges between 9 and 26% shortening (assuming a plane strain and constant volume). Where strains are less, bedding fissility dominates. Pencil fragments are defined by intersecting fracture sets subparallel to the pre-existing bedding fissility and cleavage. Their long axes are both parallel to the bedding-cleavage intersection and to the inferred Y axis of the tectonic strain ellipsoid. Pencil development is considered to result from fracturing along both fabric anisotropies during weathering and post-tectonic stress relaxation. Pencils show variations in size and shape depending on lithology (grain size and composition), degree of initial clay preferred orientation, degree of cleavage development, type of cleavage, total bulk strain and degree of strain homogeneity. Their shape ( l / w ) however is a direct measure of total Y / Z strain since strain determinations from chlorite pressure-fringes on framboidal pyrite within the pencil fragments give ( Y Z ) = 0.913 + 0.019 (l/w) . Pencil structure is therefore a potential strain marker in weakly deformed rocks.

Cataclasites along the Saltville thrust, U.S.A. and their implications for thrust-sheet emplacement

Abstract Cataclasis and frictional wear are the primary bulk deformation mechanisms along steeply dipping portions of the Saltville thrust in the southern Appalachian foreland zone, U.S.A. Fault character ranges from a single discrete sliding surface with negligible gouge, to a zone of several discrete sliding surfaces or a zone (up to 0.3 m thick) of pervasive cataclasite. Marked fracturing occurs up to 20 m above the fault, whereas minimal deformation is found in the footwall rocks. Hanging wall dolomites range from crush breccias (less than 5% matrix) to ultracataclasites (with 90% matrix), although cataclasites (50–70% matrix) are predominant. Foliated cataclasites occur where dolomite is thrust over shale. Progressive development of cataclastic fabrics is due to comminution by fracturing and grinding along intersecting fractures. Continued frictional grinding results in complete disruption of the original fabric to produce cataclasite and minor ultracataclasite. Grain alignment occurs by rigid body rotation with subsequent local enhancement by pressure-solution. Microstructural relations of the fault gouge suggest periodic fluctuations in fluid pressure, where λ v (ratio of fluid to overburden pressure) probably ranged between 0.45 and 1. The Saltville thrust-sheet emplacement must have occurred in a caterpillar-like fashion involving aseismic and seismic shear. Shear stresses accompanying fault motion as determined from dolomite twin lamellae are in the order of 65 mPa.

Compound tectonic fabrics in singly folded rocks from southwest Virginia U.S.A.

Abstract A compound tectonic fabric is associated with folded and faulted calcareous mudrock in the foreland fold-and thrust-belt of the Appalachian orogen. Two approximately coplanar spaced cleavages evolved during one episode of folding. An earlier close-spaced (40 μ spacing) domainal microfabric is overprinted by, and transitional with a wider spaced (2–3 cm spacing), spaced-disjunctive cleavage. Development of the spaced cleavage from the domainal microfabric is considered due to a change in dominant deformation-mode from controlled grain-boundary sliding to pressure-solution. Factors which determine whether single or compound cleavage fabrics develop in singly folded rocks may relate to the timing of cleavage-forming deformation increments relative to metamorphic dehydration-reactions. At low metamorphic grade (anchimetamorphism to low greenschist facies) it is proposed that grain-alignment cleavage will develop when reactions are concomitant with deformation, whereas a spaced cleavage will develop when reactions are inhibited or have gone to completion. Compound tectonic fabrics result when reactions either undergo completion or are initiated during the period of cleavage formation. There are three distinct geometrical associations of compound fabrics and folds. These associations are determined by the relative timing of formation of the various cleavages with respect to the folding.

Enhanced sensitivity to direct current magnetic field changes in Metglas/Pb(Mg1/3Nb2/3)O3–PbTiO3 laminates

We have developed Metglas/Pb(Mg1/3Nb2/3)O3–PbTiO3 magnetoelectric (ME) laminates that have notably larger ME coefficients, with maximum values of up to 45 V/cmu2005Oe. Based on this giant ME effect, the dc magnetic field sensitivity for Metglas/PMN–PT laminate sensors was improved by a factor of >u20093, relative to that for Metglas/Pb(Zr,Ti)O3 (PZT)-based ones of the same geometry. Our new ME sensor can detect dc magnetic field changes as small as (i) 5 nT at 1 kHz and (ii) 1 nT near the resonant frequency in a shield chamber.

FURTHER ADVANCES TOWARD A MODEL OF GYPSY MOTH (LYMANTRIA DISPAR (L.)) EGG PHENOLOGY: RESPIRATION RATES AND THERMAL RESPONSIVENESS DURING DIAPAUSE, AND AGE-DEPENDENT DEVELOPMENTAL RATES IN POSTDIAPAUSE

Abstract Measurements of respiration rates were used to support a three-phase model of gypsy moth egg development. Respiration rate was measured on individual eggs that had been reared for 0–155 days at 5 °C following diapause initiation. Diapause termination was indicated by the dramatic increase in respiration rate that began approximately 95–125 days after diapause initiation. Respiration rates at 25 °C increased each day by approximately 0.0054 μl CO2/24 h during diapause. After diapause termination respiration rates increased each day approximately 0.1379 μl CO2/24 h. Eggs were equally responsive to temperature changes during diapause and postdiapause. A 10 °C increase in temperature resulted in a 2-fold increase in respiration rate. Developmental rates in postdiapause were found to be age- and temperature-dependent. The initial developmental rate parameters and a temperature-dependent rate change parameter were estimated empirically and a composite function was derived to describe the age- and temperature-dependent behavior of the developmental rate response. Modeled rates increased from 0.0 and 0.078 day−1 at postdiapause initiation to 0.01 and 0.20 day−1 at physiological age 0.95, at 5 and 30 °C respectively.

Interrelations of mesoscopic structures and strain across a small regional fold, Virginia Appalachians

Abstract Small regional folds, such as the Clover Hollow anticline of the Narrows thrust-sheet in southwest Virginia, U.S.A., are considered to be large buckle folds expressing lateral shortening above a subsurface decollement. Cleavage, mesoscopic and regional folds, and contraction faults have developed in these rocks under anchimetamorphic conditions, in a single, protracted deformation during thrust-sheet emplacement. The contraction faults dominate the structure at all scales. Three fault associations (isolated contraction faults, contraction faults in series and complex fault zones with intense folding) determine the pattern and intensity of local structures. Regional displacement transfer of strain along and across faults has produced local variations in structural style. Duplex-like systems of second-order faults terminate laterally into zones of intense folding and third-order faulting. Fold tightness, cleavage intensity, strain magnitude and total longitudinal strain ( e T ) are maximum in these regions. Contraction faults in this thrust-sheet have propagated along zones of high strain rate associated with mesoscopic folding and intense cleavage. Regional hinge migration, and greater structural complexity along the southeast limb of the Clover Hollow anticline, are considered to be due to emplacement of the adjacent thrust-sheet.