95 research outputs found
Exploring the Duality between Product and Organizational Architectures: A Test of the Mirroring Hypothesis
A variety of academic studies argue that a relationship exists between the structure of an organization and the design of the products that this organization produces. Specifically, products tend to "mirror" the architectures of the organizations in which they are developed. This dynamic occurs because the organization's governance structures, problem solving routines and communication patterns constrain the space in which it searches for new solutions. Such a relationship is important, given that product architecture has been shown to be an important predictor of product performance, product variety, process flexibility and even the path of industry evolution. We explore this relationship in the software industry. Our research takes advantage of a natural experiment, in that we observe products that fulfill the same function being developed by very different organizational forms. At one extreme are commercial software firms, in which the organizational participants are tightly-coupled, with respect to their goals, structure and behavior. At the other, are open source software communities, in which the participants are much more loosely-coupled by comparison. The mirroring hypothesis predicts that these different organizational forms will produce products with distinctly different architectures. Specifically, loosely-coupled organizations will develop more modular designs than tightly-coupled organizations. We test this hypothesis, using a sample of matched-pair products. We find strong evidence to support the mirroring hypothesis. In all of the pairs we examine, the product developed by the loosely-coupled organization is significantly more modular than the product from the tightly-coupled organization. We measure modularity by capturing the level of coupling between a product's components. The magnitude of the differences is substantial - up to a factor of eight, in terms of the potential for a design change in one component to propagate to others. Our results have significant managerial implications, in highlighting the impact of organizational design decisions on the technical structure of the artifacts that these organizations subsequently develop.Organizational Design, Product Design, Architecture, Modularity, Open-Source Software.
Pion-Nucleus Scattering at Medium Energies with Densities from Chiral Effective Field Theories
Recently developed chiral effective field theory models provide excellent
descriptions of the bulk characteristics of finite nuclei, but have not been
tested with other observables. In this work, densities from both relativistic
point-coupling models and mean-field meson models are used in the analysis of
meson-nucleus scattering at medium energies. Elastic scattering observables for
790
MeV/ on Pb are calculated in a relativistic impulse
approximation, using the Kemmer-Duffin-Petiau formalism to calculate the
nucleus optical potential.Comment: 9 page
The Architecture of Complex Systems: Do Core-periphery Structures Dominate?
Any complex technological system can be decomposed into a number of subsystems
and associated components, some of which are core to system function while others are
only peripheral. The dynamics of how such “core-periphery” structures evolve and
become embedded in a firm’s innovation routines has been shown to be a major factor in
predicting survival, especially in turbulent technology-based industries. To date
however, there has been little empirical evidence on the propensity with which coreperiphery
structures are observed in practice, the factors that explain differences in the
design of such structures, or the manner in which these structures evolve over time.
We address this gap by analyzing a large number of systems in the software industry.
Our sample includes 1,286 software releases taken from 19 distinct applications. We find
that 75-80% of systems possess a core-periphery structure. However, the number of
components in the core varies widely, even for systems that perform the same function.
These differences appear to be associated with different models of development – open,
distributed organizations developing systems with smaller cores. We find that core
components are often dispersed throughout a system, making their detection and
management difficult for a system architect. And we show that systems evolve in
different ways – in some, the core is stable, whereas in others, it grows in proportion to
the system, challenging the ability of an architect to understand all possible component
interactions. Our findings represent a first step in establishing some stylized facts about
the structure of real world systems
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Hidden Structure: Using Network Methods to Map Product Architecture
In this paper, we describe an operational methodology for characterizing the architecture of complex technical systems and demonstrate its application to a large sample of software releases. Our methodology is based upon directed network graphs, which allows us to identify all of the direct and indirect linkages between the components in a system. We use this approach to define three fundamental architectural patterns, which we label Core—periphery, multi-core, and hierarchical. Applying our methodology to a sample of 1,286 software releases from 17 applications, we find that the majority of releases possess a "core-periphery" structure. This architecture is characterized by a single dominant cyclic group of components (the "Core") that is large relative to the system as a whole as well as to other cyclic groups in the system. We show that the size of the Core varies widely, even for systems that perform the same function. These differences appear to be associated with different models of development—open, distributed organizations develop systems with smaller Cores, while closed, co-located organizations develop systems with larger Cores. Our findings establish some "stylized facts" about the fine-grained structure of large, real-world technical systems, serving as a point of departure for future empirical work
Pitch period segmentation and spectral representation of speech signals
Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1999.Includes bibliographical references (leaves 87-88).by John Joseph Rusnak, Junior.M.Eng
Relativistic Point-Coupling Models as Effective Theories of Nuclei
Recent studies have shown that concepts of effective field theory such as
naturalness can be profitably applied to relativistic mean-field models of
nuclei. Here the analysis by Friar, Madland, and Lynn of naturalness in a
relativistic point-coupling model is extended. Fits to experimental nuclear
data support naive dimensional analysis as a useful principle and imply a
mean-field expansion analogous to that found for mean-field meson models.Comment: 26 pages, REVTeX 3.0 with epsf.sty, plus 5 figure
Resolving subunit degeneracy with nonsymmetric pseudocontact shifts
Protein Science (2002), 11:2464–2470Desulfovibrio gigas desulforedoxin (Dx) consists of two identical peptides, each containing one [Fe-4S]center per monomer. Variants with different iron and zinc metal compositions arise when desulforedoxin is
produced recombinantly from Escherichia coli. The three forms of the protein, the two homodimers
[Fe(III)/Fe(III)]Dx and [Zn(II)/Zn(II)]Dx, and the heterodimer [Fe(III)/Zn(II)]Dx, can be separated by ion exchange chromatography on the basis of their charge differences. Once separated, the desulforedoxins
containing iron can be reduced with added dithionite. For NMR studies, different protein samples were prepared labeled with 15N or 15N + 13C. Spectral assignments were determined for [Fe(II)/Fe(II)]Dx and
[Fe(II)/Zn(II)]Dx from 3D 15N TOCSY-HSQC and NOESY-HSQC data, and compared with those reported previously for [Zn(II)/Zn(II)]Dx. Assignments for the 13C shifts were obtained from an HNCA experiment.
Comparison of 1H–15N HSQC spectra of [Zn(II)/Zn(II)]Dx, [Fe(II)/Fe(II)]Dx and [Fe(II)/Zn(II)]Dx revealed that the pseudocontact shifts in [Fe(II)/Zn(II)]Dx can be decomposed into inter- and intramonomer components, which, when summed, accurately predict the observed pseudocontact shifts observed for
[Fe(II)/Fe(II)]Dx. The degree of linearity observed in the pseudocontact shifts for residues 8.5 Å from the metal center indicates that the replacement of Fe(II) by Zn(II) produces little or no change in the structure of Dx. The results suggest a general strategy for the analysis of NMR spectra of homo-oligomeric proteins
in which a paramagnetic center introduced into a single subunit is used to break the magnetic symmetry and make it possible to obtain distance constraints (both pseudocontact and NOE) between subunits
The Axial-Vector Current in Nuclear Many-Body Physics
Weak-interaction currents are studied in a recently proposed effective field
theory of the nuclear many-body problem. The Lorentz-invariant effective field
theory contains nucleons, pions, isoscalar scalar () and vector
() fields, and isovector vector () fields. The theory exhibits a
nonlinear realization of chiral symmetry and has three
desirable features: it uses the same degrees of freedom to describe the
axial-vector current and the strong-interaction dynamics, it satisfies the
symmetries of the underlying theory of quantum chromodynamics, and its
parameters can be calibrated using strong-interaction phenomena, like hadron
scattering or the empirical properties of finite nuclei. Moreover, it has
recently been verified that for normal nuclear systems, it is possible to
systematically expand the effective lagrangian in powers of the meson fields
(and their derivatives) and to reliably truncate the expansion after the first
few orders. Here it is shown that the expressions for the axial-vector current,
evaluated through the first few orders in the field expansion, satisfy both
PCAC and the Goldberger--Treiman relation, and it is verified that the
corresponding vector and axial-vector charges satisfy the familiar chiral
charge algebra. Explicit results are derived for the Lorentz-covariant,
axial-vector, two-nucleon amplitudes, from which axial-vector meson-exchange
currents can be deduced.Comment: 32 pages, REVTeX 4.0 with 12pt.rtx, aps.rtx, revsymb.sty,
revtex4.cls, plus 14 figures; two sentences added in Summary; two references
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Carboxylic ester hydrolases from hyperthermophiles
Carboxylic ester hydrolyzing enzymes constitute a large group of enzymes that are able to catalyze the hydrolysis, synthesis or transesterification of an ester bond. They can be found in all three domains of life, including the group of hyperthermophilic bacteria and archaea. Esterases from the latter group often exhibit a high intrinsic stability, which makes them of interest them for various biotechnological applications. In this review, we aim to give an overview of all characterized carboxylic ester hydrolases from hyperthermophilic microorganisms and provide details on their substrate specificity, kinetics, optimal catalytic conditions, and stability. Approaches for the discovery of new carboxylic ester hydrolases are described. Special attention is given to the currently characterized hyperthermophilic enzymes with respect to their biochemical properties, 3D structure, and classification
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