TVOCs and PM 2.5 in Naturally Ventilated Homes: Three Case Studies in a Mild Climate

In southern Europe, the present stock of social housing is ventilated naturally, with practice varying in the di erent seasons of the year. In winter, windows are kept closed most of the day with the exception of short periods for ventilation, whereas the rest of the year the windows are almost permanently open. In cold weather, air changes depend primarily on the air infiltrating across the envelope and when the temperature is warm, on the air flowing in through open windows. CO2, PM2.5, and TVOC concentration patterns were gathered over a year’s time in three social housing developments in southern Europe with di erent airtightness conditions and analyzed to determine possible relationships between environmental parameters and occupants’ use profiles. Correlations were found between TVOC and CO2 concentrations, for human activity was identified as the primary source of indoor contaminants: peak TVOC concentrations were related to specific household activities such as cooking or leisure. Indoor and outdoor PM2.5 concentrations were likewise observed to be correlated, although not linearly due to the presence of indoor sources. Ventilation as presently practiced in winter appears to be insufficient to dilute indoor contaminants in all three buildings, nor does summertime behavior guarantee air quality

Unravelling the complex magnetic structure of multiferroic pyroxene NaFeGe2O6: A combined experimental and theoretical study

Magnetic order and the underlying magnetic model of the multiferroic pyroxene NaFeGe2O6 are systematically investigated by neutron powder diffraction, thermodynamic measurements, density-functional bandstructure calculations, and Monte-Carlo simulations. Upon cooling, NaFeGe2O6 first reveals one-dimensional spin-spin correlations in the paramagnetic state below about 50 K, revealed by magnetic diffuse scattering. The sinusoidal spin-density wave with spins along the a-direction sets in at 13 K, followed by the cycloidal configuration with spins lying in the (ac) plane below 11.6 K. Microscopically, the strongest magnetic coupling runs along the structural chains, J1 ' 12 K, which is likely related to the one-dimensional spin-spin correlations. The interchain couplings J2 ' 3:8K and J3 ' 2:1K are energetically well balanced and compete, thus giving rise to the incommensurate order in sharp contrast to other transition-metal pyroxenes, where one type of the interchain couplings prevails. The magnetic model of NaFeGe2O6 is further completed by the weak single-ion anisotropy along the a-direction. Our results resolve the earlier controversies regarding the magnetic order in NaFeGe2O6 and establish relevant symmetries of the magnetic structures. These results, combined with symmetry analysis, enable us to identify the possible mechanisms of the magnetoelectric coupling in this compound. We also elucidate microscopic conditions for the formation of incommensurate magnetic order in pyroxenes.Comment: 10 pages 10 figures, PRB(accepted

Viable and not viable spore concentrations in National Gallery of Umbria (Italy)

AbstractThe conservation actions towards artworks holding a common patrimony for the community are of primary importance, but also those related to their "container" as museums, libraries or archives are to consider. Fungal spores and bacteria carried by air flows to the artwork surface can colonize it causing biodeterioration through physical and/or chemical alterations of the materials with the irreversible loss of their value. The quality control of the indoor air surrounding the historic building is essential, as well as for the protection and conservation of the artwork, also for the protection of the health of operators and visitors. The aim of this study was to monitor airborne fungal particles, through volumetric spore traps, for improving the knowledge about the conservation and protection of artworks in the museum environment analysing the principal relationships between indoor environmental conditions and potentially biodeteriogen fungal spore growth. The evidence of no significant relationships between spore concentrations and environmental conditions recorded inside the different expositive rooms testified the regular and correct maintenance of the air conditioning system inside the considered building (National Gallery of Umbria, central Italy). Moreover, in a specific museum room a significant spore concentration decreasing trend was recorded mainly due to a structural modification in the same building

Crisis Management on Social Media: a framework

Purpose. Scholars should investigate organization model of companies that successfully manage their Social Media presence, in every circumstance. The main purpose of our research is to provide a network perspective to the relevant topic of Social Media Crisis Management. Methodology. Following an exploratory qualitative approach, Authors have conducted 5 in-depth interviews with key Informants (internal and external to the Company) designated to the task of \u201csocial media crisis management\u201d, linked in a client/suppliers relationship. All the material has been reviewed through a content-analysis. Findings. According to our preliminary research, many are the issues and the topics that companies and digital agencies/consultants must control in their collaboration to face a Social Media crisis. Even if the topic is compelling, many of those elements are unexpected and underestimate. Practical implications. Managerial implications concern three different point of view: how companies and their suppliers interact in facing challenges online and how a network approach could be useful for Social Media Crisis Management. Originality/value. From the best of our knowledge, this study could be the first in analysing how companies and agencies must be organized to face a crisis on Social Media. Moreover, it will allow investigating in an empiric way the sense making approach to the crisis management topic

New forms of polar and spin ordering in Pb2(Mn,Co)WO6 double perovskites: symmetry analysis of ferroic properties

In recent years, the scientific community focused on the study of new materials, in which the simultaneous presence of different functionalities in the same compound represents the basis for the fabrication of multifunctional device. In this framework the multiferroics materials, in particular the magneto-electric ones, have a special place. In this type of systems the symmetry constrains, dictated from the magnetic point group, play an essential role in regulating all the physical properties and in particular the magneto-electrical coupling in the system. This Ph.D. thesis presents the study of a double perovskite system, Pb2(Mn,Co)WO6, that reveals a complex and quite interesting magneto-electric multiferroic character. The work is based on the accurate analysis of the magnetic symmetry, exploiting the use of the coloured groups and its generalization to the superspace formalism, which joined with a comprehensive physical characterization, lead to define in detail the complicated picture of the system properties. The study is mainly focused on the two end members of the solid solution and on the intermediate composition containing Mn and Co in the B site in a 50/50 ratio. The manganese end member of the solid solution displays at room temperature (RT) an unusual ferrielectric state characterized by the presence of two independent Pb sublattices. By decreasing the temperature, the system exhibits two magnetic phase transitions and a magnetic ground state characterized by an incommensurate to commensurate (IC/C) magnetic phase transition at 8 K. The magnetic structure is analysed with the use of the superspace formalism that allows an easy description of the IC/C transition. The mixed compound Pb2Mn0.5Co0.5WO6 shows an antiferroelectric character and presents a first magnetic transition at 190 K, characterized by short-range order, whereas a second magnetic transition leading to long-range order is observed at 9 K. The long-range ordered phase is an antiferromagnetic collinear structure presenting an acentric magnetic space groups, suggesting the presence of a spontaneous electrical polarization confirmed by the electrical characterization. The combined use with the magnetic symmetry suggests the symmetric exchange striction mechanism to be at the basis of the observed phenomena. The other end member presents at RT an incommensurate modulated structure that undergoes at 230 K a structural phase transition to an orthorhombic centrosymmetric structure. The magnetic structure analysis indicate a transition to an incommensurate spin structure below 12 K and, as in the previous case, the symmetry analysis suggests the presence of a spontaneous electrical polarization below the magnetic transition. Finally, joining these results with the preliminary ones obtained on other compositions, the multiferroic phase diagram of the Pb2(Mn,Co)WO6 system is sketch, pointing out, with the increase of the Co content, a transition from proper ferrielectricity to improper ferroelectricity, driven by the breaking of the centrosymmetric character of the nuclear structure operated by the magnetism.Negli ultimi anni l'attenzione della comunità scientifica si è incentrata sullo studio di nuovi materiali, in cui la simultanea presenza di funzionalità diverse diventa la chiave di sviluppo di nuovi dispositivi multifunzionali. In tale scenario i materiali multiferroici, in particolare quelli magneto-elettrici, godono di un posto speciale. Infatti, in questi sistemi, i vincoli di simmetria, dettati dal gruppo puntuale magnetico, svolgono un ruolo essenziale nel regolare tutte le proprietà fisiche e in particolare l'accoppiamento magneto-elettrico nel sistema. Questa tesi di dottorato presenta lo studio della soluzione solida Pb2(Mn,Co)WO6, con struttura di doppia perovskite, che mostra un carattere magneto-elettrico complesso e molto interessante. Il lavoro si basa sull’accurata analisi della simmetria magnetica, sfruttando l'uso dei gruppi spaziali colorati e della loro generalizzazione al formalismo del superspazio, che unita ad una caratterizzazione fisica esaustiva, porta alla definizione accurata delle complicate proprietà del sistema. Lo studio è principalmente focalizzato sui due end-members della soluzione solida e sulla composizione intermedia, contenente Mn e Co in sito B in un rapporto 50/50. L’end-member contenente solo manganese mostra a temperatura ambiente (RT) uno stato ferrielettrico caratterizzato dalla presenza di due sotto-reticoli indipendenti del piombo. Abbassando la temperatura, il sistema mostra due transizioni magnetiche e uno stato fondamentale caratterizzato dalla transizione fra una struttura incommensurata e commensurata (IC/C) a 8 K. La struttura magnetica è stata risolta con l’utilizzo del superspazio, che permette facilmente di caratterizzare la transizione IC/C. Il composto Pb2Mn0.5Co0.5WO6 presenta invece una struttura ortorombica centro-simmetrica caratteristica di un sistema anti-ferroelettrico e mostra una prima transizione magnetica a 190 K, caratterizzata da un ordine a corto range, seguita da una seconda transizione a 9 K, che porta l’ordine a lungo range. La struttura magnetica di questa fase consiste in un arrangiamento antiferromagnetico collineare dei momenti e presenta un gruppo di simmetria magnetico acentrico, suggerendo la presenza di una polarizzazione elettrica spontanea. La caratterizzazione elettrica conferma la presenza di questa polarizzazione e l'uso combinato della simmetria magnetica suggerisce che alla base dei fenomeni osservati ci sia un meccanismo di tipo “symmetric exchange striction”. L’altro end-member del sistema presenta a RT una struttura modulata incommensurata, che a 230 K si trasforma in una struttura ortorombica centro-simmetrica. L'analisi magnetica mostra una transizione a 12 K verso una struttura incommensurata, per la quale l’analisi della simmetria suggerisce la presenza di polarizzazione elettrica spontanea. Questi risultati, unitamente a quelli preliminari ottenuti su altre composizioni della soluzione solida, permettono infine di costruire il diagramma di fase multiferroico del sistema, in cui all’aumentare del contenuto di Co, si passa da una ferrielettricità propria ad una ferroelettricità impropria, indotta dalla rottura del carattere centrosimmetrico della struttura nucleare da parte del magnetismo

Intermultiplet transitions and magnetic long-range order in Sm-based pyrochlores

We present bulk and neutron scattering measurements performed on the isotopically enriched $^{154}\mathrm{Sm_2Ti_2O_7}$ and $^{154}\mathrm{Sm_2Sn_2O_7}$ samples. Both compounds display sharp heat capacity anomalies, at 350 mK and 440 mK, respectively. Inelastic neutron scattering measurements are employed to determine the crystalline electric field (CEF) level scheme, which includes transitions between the ground-state and first excited $J$ multiplets of the $\mathrm{Sm}^{3+}$ ion. To further validate those results, the single-ion magnetic susceptibility of the compounds is calculated and compared with the experimental DC-susceptibility measured in low applied magnetic fields. It is demonstrated that the inclusion of intermultiplet transitions in the CEF analysis is fundamental to the understanding of the intermediate and, more importantly, low temperature magnetic behaviour of the Sm-based pyrochlores. Finally, the heat capacity anomaly is shown to correspond to the onset of an all-in-all-out long-range order in the stannate sample, while in the titanate a dipolar long-range order can be only indirectly inferred.Comment: 13 pages, 10 Figure

Coupling between spin and charge order driven by magnetic field in triangular Ising system LuFe2O4+δ

We present a study of the magnetic-field effect on spin correlations in the charge ordered triangular Ising system LuFe2O4+δ through single crystal neutron diffraction. In the absence of a magnetic field, the strong diffuse neutron scattering observed below the Neel temperature (TN = 240 K) indicates that LuFe2O4+δ shows short-range, two-dimensional (2D) correlations in the FeO5 triangular layers, characterized by the development of a magnetic scattering rod along the 1/3 1/3 L direction, persisting down to 5 K.We also found that on top of the 2D correlations, a long range ferromagnetic component associated with the propagation vector k1 = 0 sets in at around 240 K. On the other hand, an external magnetic field applied along the c-axis effectively favours a three-dimensional (3D) spin correlation between the FeO5 bilayers evidenced by the increase of the intensity of satellite reflections with propagation vector k2 = (1/3, 1/3, 3/2). This magnetic modulation is identical to the charge ordered superstructure, highlighting the field-promoted coupling between the spin and charge degrees of freedom. Formation of the 3D spin correlations suppresses both the rod-type diffuse scattering and the k1 component. Simple symmetry-based arguments provide a natural explanation of the observed phenomenon and put forward a possible charge redistribution in the applied magnetic field