402 research outputs found
Step-wise extinctions at the Cretaceous-Tertiary boundary and their climatic implications
A comparative study of planktonic foraminifera and radiolarian assemblages from the Cretaceous-Tertiary (K-T) boundary section of the Beloc Formation in the southern Peninsula of Haiti, and the lowermost Danian sequence of the Micara Formation in southern Cuba reveals a remarkable pattern of step-wise extinctions. This pattern is consistent in both places despite the widely different lithologies of the two formations. Because of a step-wise extinction and the delayed disappearance of taxa known to be more representative of cooler water realms, it is inferred that a cooling trend which characterized the close of the Maastrichtian and the onset of the Tertiary had the major adverse effect on the existing biota. Although repetitive lithologic and faunal fluctuations throughout the Maastrichtian sediments found at Deep Sea Drilling Project (DSDP) site 146/149 in the Caribbean Sea indicate variations reminiscent of known climatically induced cycles in the Cenozoic, rapid biotic succession appears to have taken place during a crisis period of a duration greater than 2 mission years. Widespread and abundant volcanic activities recorded in the Caribbean area during the crisis period gives further credence to earlier contention that intense volcanism may have played a major role in exhacerbating pre-existing climatic conditions during that time
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Paleomagnetic Results from the Cretaceous Dumisseau Formation of Haiti
Paleomagnetic studies of basalts and sediments from the Dumisseau Formation show that: 1) The basalt magnetizations are characterized by very low coercivlty components. The sediments have generally higher but more variable stabilities against alternating field (AF) treatment compared to the basalts. The 200 oe AF mean directions for the Dumlsseau basalt and sediment sites tend to fall near the present geomagnetic dipole field direction corresponding to the Latitude of Haiti. It is suggested that these rocks carry predominantly secondary magnetization of recent origin and there is little evidence for the preservation of remanent magnetization which may correspond to the time of formation of the rock units in the Late Cretaceous. 2) The remanent magnetic properties of the basalts, particularly those from the upper part of the formation in the Dumisseau area, are very similar to those reported for basalts recovered in the Caribbean DSDP Leg 15, Sites 146, 150, 151, 152 and 153, suggesting also similarities in their petrotectonic origin
Productividad cianobacteriana, variaciones del carbono orgánico y facies de la Formación Indidura (Cenomaniano-Turoniano), noreste de México
Las rocas de edad Cenomaniano-Turoniano normalmente asignadas a la Formación de Indidura en México nororiental (Estado de Coahuila) contienen facies distintivas que son indicativas de una variabilidad espacial importante a través de la plataforma de carbonatos. Se han seleccionado tres secciones estratigráficas para probar si estas diferencias existen. La sección de Las Delicias (estratotipo) esta caracterizada por capas naranja claro de biocalciruditas (10-30 centímetros de espesor). Las estructuras internas primarias están ausentes. Los aloquímicos consisten esencialmente en asociaciones ricas en fósiles de equinodermos, pelecípodos, así como amonitas y foraminíferos planctónicos. El contenido de carbonato total (CaCO3) varía entre 48% y 94%, y el contenido de carbono total orgánico (TOC) entre 0,7% y 1,5%.La sección del Cañón La Casita, está al sureste de Las Delicias. Esta consiste en capas café claro amarillento de biocalcilutitas y lutitas laminadas verde oliva a grises con espesores de 3 a 30 cm. No se observa ninguna estructura interna deposicional; en las secciones delgadas se observa claramente abundante bioturbación. Los aloquímicos esencialmente son fragmentos esparcidos de foraminíferos planctónicos y radiolarios concentrados en madrigueras. El carbonato total (CaCo3) varía entre el 0,8% y 59,3%, mientras que el TOC varia entre el 0,17% y 5,8%. En contraste con estas sucesiones pobremente laminadas, en la Sierra de Parras, al sur de La Delicias y al oeste de la Casita, la sucesión se presenta como intercalaciones rítmicas de lutitas laminadas grisverdosas y negroparduzcas con espesores de 8 a 200 cm y biocalcilutitas margosas de 5 a 100 cm de espesor. Ambas facies exhiben estructuras internas similares organizadas en forma de laminillas duales paralelas “varvas” de < 3 mm de espesor, que contienen escasos foraminíferos planctónicos esparcidos en las laminillas oscuras. No se hay restos de epifauna, salvo esporádicos pelecípodos (Inocerámidos). El contenido de carbonato total (CaCO3) varía entre 43% y 78,3%, mientras que el contenido de TOC es relativamente alto con valores entre 7,3% y 24,3%, consistentemente superiores a 20%. La observación, de las laminillas presentes en las facies del área de Parras, muestra que sus diferencias composicionales están asociadas a la variabilidad en la abundancia de esferas microscópicas o “micro-oolitos.” Estas estructuras son interpretadas como de un posible origen cianobacteriano y se entienden como ciclos que representan eventos de florecimientos de cianobacterias, las cuales permanecieron dominantes a lo largo de la sucesión. Aún más, las lutitas laminadas y biocalcilutitas negras y ricas en TOC de la región de Parras documentan unas condiciones paleoceanográficas únicas, las cuales estaban caracterizadas por aguas oceánicas relativamente pobres en oxígeno.La distribución de la epifauna y las variaciones de carbón/carbonato en la región de Parras, sugieren que en los fondos de acumulación hubo fuertes eventos rítmicos de disoxia/anoxia. Esto contrasta claramente con los sedimentos de las áreas de Las Delicias y de La Casita, en las que se documentan condiciones del fondo diferentes, donde la epifauna bentónica y la fauna planctónica y nectónica pudieron proliferar. Asumiendo que estas facies son coetáneas, los análisis de microfacies y de TOC de estas rocas demuestran aún más las diferencias entre estas áreas
Towards new insights in the phylogeny of the Spermacoce clade: an integrative taxonomic approach using morphology, anatomy, ecology and phylogenetics reveáis the new genus Leonoria
Phylogenetic inference analyses o f two nuclear and four plastid DNA markers from 82 accessions representing 19 genera o f the Spermacoce clade (Spermacoceae-Rubiaceae) confirm that the Brazilian genus Denscantia is biphyletic. By the analyses o f reproductive morphological characters, foliar morpho-anatomy and histochemical, geographical distribution ranges, and ecological niche derived from climatic space, Denscantia caldcóla is shown as a distinct lineage from the other Denscantia species, indicating its taxonomic segregation into a new monospecific genus Leonoria. Significant morphological diíferences o f Leonoria with Denscantia were found in inflorescence organization, stigma shape, fruit dehiscence, and pollen morphology. Morphoanatomical variation among leaf traits were found in epidemial cells, occurrence o f trichomes, mesophyll histochemical, and vascular organization. Analysis o f occurrence records o f 205 specimens demonstrates a clear ecological distinction between o f Denscantia s.s. and Leonoria, which is ecologically confined to limestone outcrops associated with seasonally dry forests. The current study demonstrates the importance of an integrative taxonomic approach - in which múltiple disciplines are combined - to the unravel complex taxonomic pattems within Rubiaceae. The genus Leonoria, to be newly described, is dedicated to Professor Elsa Leonor Cabral
A Large Brightness Enhancement of the QSO 0957+561 A Component
We report an increase of more than 0.2 mag in the optical brightness of the
leading image (A) of the gravitational lens Q0957+561, detected during the
09/2000 -- 06/2001 monitoring campaign (2001 observing season). The brightening
is similar to or even greater than the largest change ever detected during the
20 years of monitoring of this system. We discuss two different provisional
explanations to this event: intrinsic source variability or microlensing
(either short timescale microlensing or cessation of the historical
microlensing). An exhaustive photometric monitoring of Q0957+561 is needed
until summer of 2002 and during 2003 to discriminate between these
possibilities.Comment: 13 pages including 3 figures and 1 table. Accepted for publication in
ApJ Let
Erasure Techniques in MRD codes
This book is organized into six chapters. The first chapter introduces the
basic algebraic structures essential to make this book a self contained one.
Algebraic linear codes and their basic properties are discussed in chapter two.
In chapter three the authors study the basic properties of erasure decoding in
maximum rank distance codes. Some decoding techniques about MRD codes are
described and discussed in chapter four of this book. Rank distance codes with
complementary duals and MRD codes with complementary duals are introduced and
their applications are discussed. Chapter five introduces the notion of integer
rank distance codes. The final chapter introduces some concatenation
techniques.Comment: 162 pages; Published by Zip publishing in 201
Unfolding the Labyrinth: Open Problems in Mathematics, Physics, Astrophysics, and Other Areas of Science
Throughout this book, we discuss some open problems in various branches of
science, including mathematics, theoretical physics, astro-physics, geophysics
etc. It is of our hope that some of the problems discussed in this book will
find their place either in theoretical exploration or further experiments,
while some parts of these problems may be found useful for scholarly
stimulation. The present book is also intended for young physics and
mathematics fellows who will perhaps find the unsolved problems described here
are at least worth pondering. If this book provides only a few highlights of
plau-sible solutions, it is merely to keep the fun of readers in discovering
the answers by themselves.Comment: 139 pages, many figure
Easier to break from inside than from outside / Mai ușor să distrugi din interior decât din exterior
Abstract in English:
This book contains concrete examples from history, economy, biology, digital world, nuclear physics, agriculture and so on about breaking a neutrosophic dynamic system (i.e. a dynamic system that has indeterminacy) from inside.
We define a neutrosophic mathematical model using a system of ordinary differential equations and the neutrosophic probability in order to approximate the process of breaking from inside a neutrosophic complex dynamic system.
It shows that for breaking from inside it is needed a smaller force than for breaking from outside the neutrosophic complex dynamic system.
Methods that have been used in the past for breaking from inside are listed.
Simulation and animation of this neutrosophic dynamical system are needed for the future since, by changing certain parameters, various types of breaking from inside may be simulated.
Abstract in Romana:
Această carte conține exemple concrete din istorie, economie, biologie, spațiu digital, fizică nucleară, agricultură și altele, de distrugere unui sistem neutrosofic dinamic (adică a unui sistem care are indeterminări), acționând din interiorul acestuia.
Descriem un model neutrosofic matematic folosind un sistem de ecuații diferențiale ordinare și probabilitatea neutrosofică, cu scopul de a aproxima procesul de distrugere din interior a unui sistem neutrosofic dinamic complex.
Se demonstrează că, pentru distrugerea din interior a unui astfel de sistem, este necesară o forță mai mică decât pentru distrugerea din exterior.
Sunt enumerate metode folosite în trecut pentru distrugerea din interior.
Simularea și animația acestui sistem neutrosofic dinamic sunt necesare pentru viitor, deoarece, schimbând diferiți parametri, se pot simula diferite tipuri de distrugeri din interior
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