3,215 research outputs found
Government spending shocks and labor productivity
A central question in the empirical fiscal policy literature is the magnitude, in fact even
the sign, of the fiscal multiplier. Standard identification schemes for fiscal VAR models
typically imply positive output as well as labor productivity responses to expansionary
government spending shocks. The standard macro assumption of decreasing returns to
labor, however, implies that expansionary government spending shocks should lead to
increasing output and hours, but to decreasing labor productivity. To potentially reconcile
theory and empirical analysis we impose, amongst other sign restrictions, opposite signs
of the impulse responses of output and labor productivity to government spending shocks
in eight- to ten-variable VAR models, estimated on quarterly US data. Doing so leads to
contractionary effects of positive government spending shocks. This potentially surprising
finding is robust to the inclusion of variable capital utilization rates and total factor
productivity
Inherited arc signature in Ediacaran and Early Cambrian basins of
Geochemical data from clastic rocks of the Ossa-Morena Zone (Iberian Massif) show that the main source for the Ediacaran
and the Early Cambrian sediments was a recycled Cadomian magmatic arc along the northern Gondwana margin. The geodynamic
scenario for this segment of the Avalonian-Cadomian active margin is considered in terms of three main stages: (1) The 570–540 Ma
evolution of an active continental margin evolving oblique collision with accretion of oceanic crust, a continental magmatic arc
and the development of related marginal basins; (2) the Ediacaran–Early Cambrian transition (540–520 Ma) coeval with important
orogenic magmatism and the formation of transtensional basins with detritus derived from remnants of the magmatic arc; and (3)
Gondwana fragmentation with the formation of Early Cambrian (520–510 Ma) shallow-water platforms in transtensional grabens
accompanied by rift-related magmatism. These processes are comparable to similar Cadomian successions in other regions of
Gondwanan Europe and Northwest Africa. Ediacaran and Early Cambrian basins preserved in the Ossa-Morena Zone (Portugal
and Spain), the North Armorican Cadomian Belt (France), the Saxo-Thuringian Zone (Germany), the Western Meseta and the
Western High-Atlas (Morocco) share a similar geotectonic evolution, probably situated in the same paleogeographic West African
peri-Gondwanan region of the Avalonian-Cadomian active margin
The provenance of Late Ediacaran and Early Ordovician siliciclastic rocks in the
U–Pb geochronology of detrital zircon from Late Ediacaran (Beiras Group greywackes) and Early Ordovician
(Sarnelhas arkosic quartzites and Armorican quartzites of Penacova) sedimentary rocks of the
southwest Central Iberian Zone (SW CIZ) constrain the evolution of northern Gondwana active-passive
margin transition. The LA-ICP-MS U–Pb data set (375 detrital zircons with 90–110% concordant ages) is
dominated by Neoproterozoic ages (75% for the greywakes and 60% for the quartzites), among which the
main age cluster (more significant for Beiras Group greywackes) is Cryogenian (c.840–750 Ma), while a
few Mesoproterozoic and Tonian ages are also present (percentages <8%). These two features, and the
predominance of Cryogenian ages over Ediacaran ages, distinguish the Beiras Group greywackes (SW
CIZ) from the time-equivalent Serie Negra (Ossa-Morena Zone – OMZ), with which they are in inferred
contact. The age spectra of the Beiras Group greywackes also reveal three major episodes of zircon crystallisation
in the source area during the Neoproterozoic that are probably associated with a long-lived
system of magmatism that developed either along or in the vicinity of the northern Gondwana margin
at: (1) c. 850–700 Ma – Pan-African suture (not well represented in OMZ); (2) c. 700–635 Ma – early
Cadomian arc; and (3) c. 635–545 Ma – late Cadomian arc. Comparison of Neoproterozoic ages and those
of the Paleoproterozoic (c. 2–1.8 Ga) and Archean (mainly Neoarchean – 2.8–2.6 Ga, but also older) in the
Beiras Group greywackes with U–Pb ages of Cadomian correlatives shows that: (1) SW CIZ, OMZ, Saxo-
Thuringian Zone, North Armorican Cadomian Belt and Anti-Atlas) evolved together during the formation
of back-arc basins on the northern Gondwana active margin and (2) all recorded synorogenic basins that
were filled during the Ediacaran by detritus resulting from erosion of the West African craton, the Pan-
African suture and a long-lived Cadomian magmatic arc. Differences in detrital zircon age populations in
the greywackes of the Beiras Group (SW CIZ Cadomian basement) and the Serie Negra (OMZ Cadomian
basement) are also observed in their respective overlying Early Ordovician quartzites. Since both these
SW Iberia Cadomian basements evolved together along the active margin of Gondwana (but sufficiently
separated to account for the differences in their detrital zircon content), this continuation of differing
zircon populations into the Early Ordovician suggests that the inferred contact presently juxtaposing
the Beiras Group and the Serie Negra is not pre-Early Ordovician and so is unlikely to demonstrate a
Cadomian suture
Idades U-Pb dos zircões detrÃticos do Grupo das Beiras - implicações para a evolução do SW da Ibéria durante o Neoproterozóico
Evidence formulti-cycle sedimentation and provenance constraints from
Laser ablation ICP-MS U–Pb analyses were conducted on detrital zircons of Triassic sandstone and conglomerate
from the Lusitanian basin in order to: i) document the age spectra of detrital zircon; ii) compare U–Pb detrital
zircon ages with previous published data obtained from Upper Carboniferous, Ordovician, Cambrian and Ediacaran
sedimentary rocks of the pre-Mesozoic basement of western Iberia; iii) discuss potential sources; and iv) test the
hypothesis of sedimentary recycling. U–Pb dating of zircons established a maximum depositional age for this
deposit as Permian (ca. 296Ma),which is about sixty million years older compared to the fossil content recognized
in previous studies (Upper Triassic). The distribution of detrital zircon ages obtained points to common source
areas: the Ossa–Morena and Central Iberian zones that outcrop in and close to the Porto–Tomar fault zone. The
high degree of immaturity and evidence of little transport of the Triassic sediment suggests that granite may
constitute primary crystalline sources. The Carboniferous age of ca. 330 Ma for the best estimate of crystallization
for a granite pebble in a Triassic conglomerate and the Permian–Carboniferous ages (ca. 315Ma) found in detrital
zircons provide evidence of the denudation of Variscan and Cimmerian granites during the infilling of continental
rift basins in western Iberia. The zircon age spectra found in Triassic strata are also the result of recycling from the
Upper Carboniferous Buçaco basin,which probably acted as an intermediate sediment repository.U–Pb data in this
study suggest that the detritus from the Triassic sandstone and conglomerate of the Lusitanian basin is derived
fromlocal source areas with features typical of Gondwana,with no sediment from external sources from Laurussia
or southwestern Iberia
TeV Gamma-Ray Sources from a Survey of the Galactic Plane with Milagro
A survey of Galactic gamma-ray sources at a median energy of ~20 TeV has been
performed using the Milagro Gamma Ray Observatory. Eight candidate sources of
TeV emission are detected with pre-trials significance in the
region of Galactic longitude and latitude
. Four of these sources, including the Crab nebula
and the recently published MGRO J2019+37, are observed with significances
after accounting for the trials involved in searching the 3800
square degree region. All four of these sources are also coincident with EGRET
sources. Two of the lower significance sources are coincident with EGRET
sources and one of these sources is Geminga. The other two candidates are in
the Cygnus region of the Galaxy. Several of the sources appear to be spatially
extended. The fluxes of the sources at 20 TeV range from ~25% of the Crab flux
to nearly as bright as the Crab.Comment: Submitted to Ap
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