Markovian master equations for quantum thermal machines: local vs global approach

The study of quantum thermal machines, and more generally of open quantum systems, often relies on master equations. Two approaches are mainly followed. On the one hand, there is the widely used, but often criticized, local approach, where machine sub-systems locally couple to thermal baths. On the other hand, in the more established global approach, thermal baths couple to global degrees of freedom of the machine. There has been debate as to which of these two conceptually different approaches should be used in situations out of thermal equilibrium. Here we compare the local and global approaches against an exact solution for a particular class of thermal machines. We consider thermodynamically relevant observables, such as heat currents, as well as the quantum state of the machine. Our results show that the use of a local master equation is generally well justified. In particular, for weak inter-system coupling, the local approach agrees with the exact solution, whereas the global approach fails for non-equilibrium situations. For intermediate coupling, the local and the global approach both agree with the exact solution and for strong coupling, the global approach is preferable. These results are backed by detailed derivations of the regimes of validity for the respective approaches.Comment: Published version. See also the related work by J. Onam Gonzalez et al. arXiv:1707.0922

Why Sparing the Rod Does Not Spoil the Child: A Critique of the "Strict Father” Model in Transnational Governance

The United Nations Global Compact (UNGC) is one of the largest transnational governance schemes (TGSs). Its success or failure, however, is a matter of debate. Drawing on research in cognitive linguistics, we argue that when evaluators discuss the UNGC, they apply the metaphorical concept of the family: the UNGC corresponds to the "family,” the UNGC headquarter to the "parent” and the business participants of the UNGC to the "children” of the family. As a corollary, evaluators' implicit understanding of how a family is best organized sets different benchmarks against which the governance structure of the UNGC is assessed. We describe two ideal models of "educating” UNGC business participants. Critics of the UNGC adopt a "strict father” model of transnational governance based on the idea that the proper education of inherently "bad” business firms necessitates obedience, discipline and punishment in case firms are non-compliant. In contrast, the UNGC's advocates follow a "nurturant parent” model, which prioritizes empathy, learning and nurturance to support the moral development of "good” business firms. We develop the "UNGC-as-family” metaphor, explore its implications for transnational governance and discuss under what conditions these idealized models can serve as appropriate guidelines for TGSs. Specifically, we posit that following the behavioral prescriptions of the "strict father” model may, under certain conditions, jeopardize the organizational embedding and institutionalization of UNGC principles, and explain when and why it may be in the best interest of the UNGC and civil society to embrace the instructions of the "nurturant parent” model of transnational governance

Von rhetorischer zu organisationaler Realität? Die globale Standardisierung von Unternehmensverantwortung als diskursiver Aushandlungsprozess

"In diesem Beitrag untersuchen die Autoren den Prozess der globalen Standardisierung von Maßnahmen der Corporate Social Responsibility (CSR). Unter Rückgriff auf Theorieansätze des Neuen Soziologischen Institutionalismus unterscheiden sie hierbei zwischen der Breiten- und Tiefendimension von CSR-Standardisierungsprozessen. Am Beispiel des 'Equator Principles'- Standards in der internationalen Projektfinanzierungsindustrie zeigen sie auf, dass sich CSR-Standards innerhalb einer Industrie zwar rasch und weit verbreiten können (Breitendimension), dass jedoch erst diskursive Aushandlungsprozesse zwischen den beteiligten Akteuren mithin darüber bestimmen, ob und inwieweit die Außendarstellung mit der tatsächlichen Implementierung von Organisationspraktiken (Tiefendimension) in Einklang gebracht wird." (Autorenreferat)"In this paper, the authors examine the process of global corporate social responsibility (CSR) standardization. By drawing on neo-institutionalist theories they distinguish between the breadth and depth dimension of CSR standardization. Based on their empirical study of the 'Equator Principles', a CSR standard in the field of international project finance, they exemplify that CSR standards indeed can disseminate rapidly and widely within an industry (breadth dimension). However, they also show that their impact is contingent upon discursive negotiation processes that affect whether the formal adoption of a standard is perceived as meaningful and legitimate, in turn engendering the actual organizational implementation of practices (depth dimension)." (author's abstract

Markovian master equations for quantum thermal machines: local versus global approach

The study of quantum thermal machines, and more generally of open quantum systems, often relies on master equations. Two approaches are mainly followed. On the one hand, there is the widely used, but often criticized, local approach, where machine sub-systems locally couple to thermal baths. On the other hand, in the more established global approach, thermal baths couple to global degrees of freedom of the machine. There has been debate as to which of these two conceptually different approaches should be used in situations out of thermal equilibrium. Here we compare the local and global approaches against an exact solution for a particular class of thermal machines. We consider thermodynamically relevant observables, such as heat currents, as well as the quantum state of the machine. Our results show that the use of a local master equation is generally well justified. In particular, for weak inter-system coupling, the local approach agrees with the exact solution, whereas the global approach fails for non-equilibrium situations. For intermediate coupling, the local and the global approach both agree with the exact solution and for strong coupling, the global approach is preferable. These results are backed by detailed derivations of the regimes of validity for the respective approaches

Sengers syndrome: six novel AGK mutations in seven new families and review of the phenotypic and mutational spectrum of 29 patients

Background: Sengers syndrome is an autosomal recessive condition characterized by congenital cataract, hypertrophic cardiomyopathy, skeletal myopathy and lactic acidosis. Mutations in the acylglycerol kinase (AGK) gene have been recently described as the cause of Sengers syndrome in nine families. Methods: We investigated the clinical and molecular features of Sengers syndrome in seven new families; five families with the severe and two with the milder form. Results: Sequence analysis of AGK revealed compound heterozygous or homozygous predicted loss-of-function mutations in all affected individuals. A total of eight different disease alleles were identified, of which six were novel, homozygous c.523_524delAT (p.Ile175Tyrfs*2), c.424-1G > A (splice site), c.409C > T (p.Arg137*) and c.877 + 3G > T (splice site), and compound heterozygous c.871C > T (p.Gln291*) and c.1035dup (p.Ile346Tyrfs*39). All patients displayed perinatal or early-onset cardiomyopathy and cataract, clinical features pathognomonic for Sengers syndrome. Other common findings included blood lactic acidosis and tachydyspnoea while nystagmus, eosinophilia and cervical meningocele were documented in only either one or two cases. Deficiency of the adenine nucleotide translocator was found in heart and skeletal muscle biopsies from two patients associated with respiratory chain complex I deficiency. In contrast to previous findings, mitochondrial DNA content was normal in both tissues. Conclusion: We compare our findings to those in 21 previously reported AGK mutation-positive Sengers patients, confirming that Sengers syndrome is a clinically recognisable disorder of mitochondrial energy metabolism

Rare mutations in SQSTM1 modify susceptibility to frontotemporal lobar degeneration

Mutations in the gene coding for Sequestosome 1 (SQSTM1) have been genetically associated with amyotrophic lateral sclerosis (ALS) and Paget disease of bone. In the present study, we analyzed the SQSTM1 coding sequence for mutations in an extended cohort of 1,808 patients with frontotemporal lobar degeneration (FTLD), ascertained within the European Early-Onset Dementia consortium. As control dataset, we sequenced 1,625 European control individuals and analyzed whole-exome sequence data of 2,274 German individuals (total n = 3,899). Association of rare SQSTM1 mutations was calculated in a meta-analysis of 4,332 FTLD and 10,240 control alleles. We identified 25 coding variants in FTLD patients of which 10 have not been described. Fifteen mutations were absent in the control individuals (carrier frequency < 0.00026) whilst the others were rare in both patients and control individuals. When pooling all variants with a minor allele frequency < 0.01, an overall frequency of 3.2 % was calculated in patients. Rare variant association analysis between patients and controls showed no difference over the whole protein, but suggested that rare mutations clustering in the UBA domain of SQSTM1 may influence disease susceptibility by doubling the risk for FTLD (RR = 2.18 [95 % CI 1.24-3.85]; corrected p value = 0.042). Detailed histopathology demonstrated that mutations in SQSTM1 associate with widespread neuronal and glial phospho-TDP-43 pathology. With this study, we provide further evidence for a putative role of rare mutations in SQSTM1 in the genetic etiology of FTLD and showed that, comparable to other FTLD/ALS genes, SQSTM1 mutations are associated with TDP-43 pathology

Tumor-derived GDF-15 blocks LFA-1 dependent T cell recruitment and suppresses responses to anti-PD-1 treatment

Immune checkpoint blockade therapy is beneficial and even curative for some cancer patients. However, the majority don't respond to immune therapy. Across different tumor types, pre-existing T cell infiltrates predict response to checkpoint-based immunotherapy. Based on in vitro pharmacological studies, mouse models and analyses of human melanoma patients, we show that the cytokine GDF-15 impairs LFA-1/β2-integrin-mediated adhesion of T cells to activated endothelial cells, which is a pre-requisite of T cell extravasation. In melanoma patients, GDF-15 serum levels strongly correlate with failure of PD-1-based immune checkpoint blockade therapy. Neutralization of GDF-15 improves both T cell trafficking and therapy efficiency in murine tumor models. Thus GDF-15, beside its known role in cancer-related anorexia and cachexia, emerges as a regulator of T cell extravasation into the tumor microenvironment, which provides an even stronger rationale for therapeutic anti-GDF-15 antibody development