617 research outputs found
The Origin of the Electromagnetic Interaction in Einstein's Unified Field Theory with Sources
Einstein's unified field theory is extended by the addition of matter terms
in the form of a symmetric energy tensor and of two conserved currents. From
the field equations and from the conservation identities emerges the picture of
a gravoelectrodynamics in a dynamically polarizable Riemannian continuum.
Through an approximate calculation exploiting this dynamical polarizability it
is argued that ordinary electromagnetism may be contained in the theory.Comment: 8 pages. Misprint in eq. 15 correcte
The Electrostatics of Einstein's Unified Field Theory
When sources are added at their right-hand sides, and g_{(ik)} is a priori
assumed to be the metric, the equations of Einstein's Hermitian theory of
relativity were shown to allow for an exact solution that describes the general
electrostatic field of n point charges. Moreover, the injunction of spherical
symmetry of g_{(ik)} in the infinitesimal neighbourhood of each of the charges
was proved to yield the equilibrium conditions of the n charges in keeping with
ordinary electrostatics. The tensor g_{(ik)}, however, cannot be the metric of
the theory, since it enters neither the eikonal equation nor the equation of
motion of uncharged test particles. A physically correct metric that rules both
the behaviour of wave fronts and of uncharged matter is the one indicated by
H\'ely. In the present paper it is shown how the electrostatic solution
predicts the structure of the n charged particles and their mutual positions of
electrostatic equilibrium when H\'ely's physically correct metric is adopted.Comment: 15 pages. Misprints corrected. To appear in General Relativity and
Gravitatio
A review of 71 cases of infected total knee arthroplasty: mid-term to long-term follow-up
Departamentul de Chirurgie Ortopedică și Reabilitare, Universitatea Tech din
Texas, Centrul de Știinţe ale Sănătaţii, Școala de Medicină Paul L. Foster, El Paso,
Texas, Statele Unite ale Americii, Departamentul de Chirurgie Ortopedică, Spitalul General Buffalo, Universitatea de Stat din New York, Buffalo, New York, Statele Unite ale Americii,
Departamentul de Chirurgie Ortopedică a Universităţii Harvard, Spitalul General Massachusetts, Boston, Statele Unite ale AmericiiIntroducere. În cadrul acestui studiu au fost evaluate caracteristici
și rezultate la termen mediu și lung ale cazurilor de
artroplastie totală de genunchi (ATG) și ale infecţiilor asociate
cu acestea, care au fost tratate prin diferite metode.
Material și metode. Studiul retrospectiv reflectă rezultatele
a 71 de cazuri de ATG, infectate și tratate în perioada august
1993 – august 2005. Datele colectate includ înregistrări medicale cu privire la sexe, clasificarea infecţiilor periprotetice
(IPP), comorbiditatea pacienţilor, criteriile de diagnostic
ale IPP, rezultatele microbiologice și histopatologice, tratamentele
chirurgicale și antimicrobiene, modalitaţile de tratament,
complicaţiile, consecinţele, precum și rezultatele tratamentului.
Nivelul de evidenţă: nivel terapeutic III.
Rezultate. Vârsta medie a pacienţilor a constituit 70 de ani
(extreme, 43–88 de ani). Mediana duratei de supraveghere –
10,8 ani (extreme, 5 – 20 de ani). Treizeci și trei (46,5%) de
pacienţi au prezentat multipli factori de risc pentru IPP. Principalii
patogeni izolaţi au fost stafilococii coagulazo-negativi
– 26 (37%), Staphylococcus aureus – 16 (22,4%). Metodele de
tratament ale ATG infectate au fost: înlocuirea în două etape
– 59 (83%) de cazuri, debridare și retenţie – 5 (7,2%) cazuri,
artrodeza – 5 (7,2%) cazuri, excizie-artroplastie – 2 (2,8%)
cazuri. La sfârșitul perioadei de supraveghere, 17 genunchi
(24%) au suportat intervenţie repetată, dintre care 10 (14%)
– îndepărtarea componentelor din cauza reinfectării. Doi genunchi
s-au reinfectat de 3 ori, trei genunchi – de două ori.
Prima reintervenţie după reinfectare a fost efectuată după 1,2
ani (mediana), cu extreme cuprinse între 0,04 și 2,5 ani. Analiza
curbelor Kaplan-Meier „de supravieţuire” a constatat că la
5 ani fără reintervenţie au ajuns 90,5% (95% CI între 85,3%
și 96,1%) dintre pacienţi, iar la 10 ani – 82% (95% CI între
70,3% și 94,5%). Scorurile Asociaţiei Genunchiului (engl. Knee
Society score): scorurile de durere, scorurile funcţionale, amplituda
mișcării (engl. range of motion, ROM) – îmbunătăţite.
Concluzii. Tratamentul ATG infectate este o sarcină dificilă,
cu rezultate nesatisfăcătoare la termen mediu și lung. Aproximativ
fiecare al patrulea pacient a necesitat o reintervenţie,
iar 14% dintre pacienţi s-au reinfectat în primii 2,5 ani. Jumă-
tate dintre pacienţii cu reinfecţie a ATG s-au reinfectat din nou.
În majoritatea cazurilor, pacienţii s-au reinfectat cu același microorganism,
dar mai virulent. Tratamentul unei ATG infectate
ar putea fi ales în funcţie de tipul de infecţie (acută sau cronică),
durata ei, stabilitatea implantului, specia agentului patogen,
calitatea și integritatea osului și ţesutului moale.Introduction. In the present study, the characteristics and
mid-term to long-term outcomes of total knee arthroplasty
(TKA) associated infections treated with different types of approaches
were evaluated.
Material and methods. A retrospective study of the results
of 71 infected TKA treated between August 1993 and
August 2005. The data included medical records, gender, periprosthetic infection (PPI) classification, patients’ comorbidities,
PPI diagnostic criteria, microbiology and histopathology
results, surgical and antimicrobial therapy, treatment
modality, complications, follow up, and treatment results.
Level of Evidence: Therapeutic Level III.
Results. Median age was 70 years (range, 43–88). Median
follow-up 10.8 years (range, 5–20). Thirty-three patients
had multiple risk-factors for PPI. The main pathogens isolated
were Coagulase-negative staphylococci 26 (37%), Staphylococcus
aureus 16 (22.4%). The treatment methods of TKA
infection were two-stage exchange in 59 (83%), debridement
and retention – 5 (7.2%), arthrodesis – 5 (7.2%), excision arthroplasty
2 (2.8%). At final follow up, 17 knees (24%) had required
reoperation: 10 knees (14%) – component removal for
reinfection. Two knees were reinfected 3 times, three knees
– two times. The median time to first reoperation for reinfection
was 1.2 years (range, 0.04–2.5 years). By Kaplan-Meier
survival analysis the estimated survivals free of reoperation
for infection were 90.5% (95% confidence intervals, 85.3% to
96.1%) at 5 years and 82% (95% confidence intervals, 70.3%
to 94.5%) at 10 years. The Knee Society scores: Pain scores,
Functional scores, ROM improved.
Conclusions. TKA infections treatment is a difficult task
leading to a high rate of unsatisfactory mid-term and longterm
results. About one forth of patient require reoperation,
14% become reinfected in first 2.5 years. Half of reinfected
patients get reinfected repeatedly. In most cases patients are
reinfected with the same microorganism but more virulent.
TKA infection treatment option should be chosen according
to the type of infection (acute or chronic), the duration of infection,
the stability of the implant, the type of microorganism
causing infection, bone quality and integrity, and the quality of
the soft-tissue
Consumption of private goods as substitutes for environmental goods in an economic growth model
We analyze growth dynamics in an economy where a private good
can be consumed as a substitute for a free access environmental good. In
this context we show that environmental deterioration may be an engine of
economic growth. To protect themselves against environmental deterioration,
economic agents are forced to increase their labour supply to increase the
production and consumption of the private good. This, in turn, further depletes
the environmental good, leading economic agents to further increase their labour
supply and private consumption and so on. This substitution process may give
rise to self-enforcing growth dynamics characterized by a lack of correlation
between capital accumulation and private consumption levels, on one side, and
economic agents’ welfare, on the other.
Furthermore, we show that agents’ self-protection consumption choices can
generate indeterminacy; that is, they can give rise to the existence of a continuum
of (Nash) equilibrium orbits leading to the same attracting fixed point or periodic
orbit
Environmental degradation and indeterminacy of equilibrium selection
This paper analyzes an intertemporal optimization problem in which agents derive utility from three goods: leisure, a public environmental good and the consumption of a produced good. The global analysis of the dynamic system generated by the optimization problem shows that global indeterminacy may arise: given the initial values of the state variables, the economy may converge to different steady states, by choosing different initial values of the control variable
Bowling alone but tweeting together: the evolution of human interaction in the social networking era
The objective of this paper is to theoretically analyze how human interaction may evolve in a world characterized by the explosion of online networking and other Web-mediated ways of building and nurturing relationships. The analysis shows that online networking yields a storage mechanism through which any individual contribution—e.g. a blog post, a comment, or a photo—is stored within a particular network and ready for virtual access by each member who connects to the network. When someone provides feedback, for example by commenting on a note, or by replying to a message, the interaction is finalized. These interactions are asynchronous, i.e. they allow individuals to relate in different moments, whenever they have time to. When the social environment is poor of participation opportunities and/or the pressure on time increases (for example due to the need to increase the working time), the stock of information and ties stored in the Internet can help individuals to defend their sociability
The {\gamma} Dor stars as revealed by Kepler : A key to reveal deep-layer rotation in A and F stars
The {\gamma} Dor pulsating stars present high-order gravity modes, which make
them important targets in the intermediate-and low-mass main-sequence region of
the Hertzsprung-Russell diagram. Whilst we have only access to rotation in the
envelope of the Sun, the g modes of {\gamma} Dor stars can in principle deliver
us constraints on the inner layers. With the puzzling discovery of unexpectedly
low rotation rates in the core of red giants, the {\gamma} Dor stars appear now
as unique targets to explore internal angular momentum transport in the
progenitors of red giants. Yet, the {\gamma} Dor pulsations remain hard to
detect from the ground for their periods are close to 1 day. While the CoRoT
space mission first revealed intriguing frequency spectra, the almost
uninterrupted 4-year photometry from the Kepler mission eventually shed a new
light on them. It revealed regularities in the spectra, expected to bear
signature of physical processes, including rotation, in the shear layers close
to the convective core. We present here the first results of our effort to
derive exploitable seismic diagnosis for mid- to fast rotators among {\gamma}
Dor stars. We confirm their potential to explore the rotation history of this
early phase of stellar evolution.Comment: 4 pages, 1 figure, proceedings of the 22nd Los Alamos Stellar
Pulsation Conference, "Wide-field variability surveys: a 21st-century
perspective" held in San Pedro de Atacama, Chile, Nov. 28-Dec. 2, 201
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