SAFETRANS: a system for 3D visibility estimation and cloud cover detection.

The estimation of visibility is of significant importance in aviation safety and forms part of the measurements routinely collected in real time to provide safety guidelines and decisions. Our work concerns the creation and implementation of a lidar-based visibility estimation system as part of the SAFETRANS research program. We created a reproducible system to (1) support standard airport equipment, (2) serve simultaneously as a visibility meter and a ceilometer reporting on cloud cover, (3) offer increased accuracy and improved capabilities compared to standardized equipment currently in use while (4) requiring minimal user training to function. This work presents the visibility estimation and cloud cover algorithms and subsequently reports on results of field tests in a number of Greek airports under various atmospheric conditions.

Bioaerosol detection over Athens, Greece using the laser induced fluorescence technique.

The challenge in today's bioaerosol monitoring is to retrieve real-time information on the qualitative and quantitative composition of the ambient air in bioparticles implicated to human health. A pilot study was conducted during March-May 2018 in Athens, Greece in order to detect bioparticles within the Planetary Boundary Layer (PBL) by implementing the LIF LiDAR (Laser-Induced Fluorescence Light Detection and Ranging) technique at an excitation wavelength of 266 nm in order to determine the major components' contribution on the total fluorescence LiDAR signals aloft (30-100 m above our site). The laboratory characterization of the prevalent pollen grains and fungal spores fluorescence signatures enabled through deconvolution the breaking down of the retrieved LIF LiDAR signals and unravelled each bioparticle's contribution. The bioaerosol occurrence and concentration, as determined by the concurrent sampling with a volumetric particle sampler, verified that the detected fluorescence is related to the fungal and pollen aerosol concentration. The results of this study are very promising for the implementation of remote sensing technology in routine detection and quantification of airborne bioparticles in real-time which is important for allergy sufferers and physicians.

From hygroscopic aerosols to cloud droplets: The HygrA-CD campaign in the Athens basin - An overview.

The international experimental campaign Hygroscopic Aerosols to Cloud Droplets (HygrA-CD), organized in the Greater Athens Area (GAA), Greece from 15 May to 22 June 2014, aimed to study the physico-chemical properties of aerosols and their impact on the formation of clouds in the convective Planetary Boundary Layer (PBL). We found that under continental (W-NW-N) and Etesian (NE) synoptic wind flow and with a deep moist PBL (~2-2.5km height), mixed hygroscopic (anthropogenic, biomass burning and marine) particles arrive over the GAA, and contribute to the formation of convective non-precipitating PBL clouds (of ~16-20µm mean diameter) with vertical extent up to 500m. Under these conditions, high updraft velocities (1-2ms-1) and cloud condensation nuclei (CCN) concentrations (~2000cm-3 at 1% supersaturation), generated clouds with an estimated cloud droplet number of ~600cm-3. Under Saharan wind flow conditions (S-SW) a shallow PBL (<1-1.2km height) develops, leading to much higher CCN concentrations (~3500-5000cm-3 at 1% supersaturation) near the ground; updraft velocities, however, were significantly lower, with an estimated maximum cloud droplet number of ~200cm-3 and without observed significant PBL cloud formation. The largest contribution to cloud droplet number variance is attributed to the updraft velocity variability, followed by variances in aerosol number concentration.

Optical, size and mass properties of mixed type aerosols in Greece and Romania as observed by synergy of lidar and sunphotometers in combination with model simulations: a case study.

A coordinated experimental campaign aiming to study the aerosol optical, size and mass properties was organized in September 2012, in selected sites in Greece and Romania. It was based on the synergy of lidar and sunphotometers. In this paper we focus on a specific campaign period (23-24 September), where mixed type aerosols (Saharan dust, biomass burning and continental) were confined from the Planetary Boundary Layer (PBL) up to 4-4.5 km height. Hourly mean linear depolarization and lidar ratio values were measured inside the dust layers, ranging from 13 to 29 and from 44 to 65sr, respectively, depending on their mixing status and the corresponding air mass pathways over Greece and Romania. During this event the columnar Aerosol Optical Depth (AOD) values ranged from 0.13 to 0.26 at 532 nm. The Lidar/Radiometer Inversion Code (LIRIC) and the Polarization Lidar Photometer Networking (POLIPHON) codes were used and inter-compared with regards to the retrieved aerosol (fine and coarse spherical/spheroid) mass concentrations, showing that LIRIC generally overestimates the aerosol mass concentrations, in the case of spherical particles. For non-spherical particles the difference in the retrieved mass concentration profiles from these two codes remained smaller than ±20%. POLIPHON retrievals showed that the non-spherical particles reached concentrations of the order of 100-140 µg/m(3) over Romania compared to 50-75 µg/m(3) over Greece. Finally, the Dust Regional Atmospheric Model (DREAM) model was used to simulate the dust concentrations over the South-Eastern Europe.

Continuous wave and passively Q-switched Nd:YAG laser with a multisegmented crystal diode-pumped at 885 nm.

Mitigation of thermal effects in a 1064 nm Nd:YAG laser is demonstrated through the combination of a multisegmented crystal rod and upper laser level pumping by diode at 885 nm toward optimizing the generated beam profile. Continuous wave (cw) and passively Q-switched operation is demonstrated obtaining 7.5 W and 2 mJ at 100 Hz, respectively, with excellent beam quality. Comparison with a conventional uniform Nd:YAG rod reveals improvements of up to 64% in optical conversion efficiency and 67% in output power for retaining the beam quality. Thermal-lensing measurements validate the improved thermal management in the multisegmented crystal in conjunction with M-square values better than 1.3.

A study on the atmospheric concentrations of primary and secondary air pollutants in the Athens basin performed by DOAS and DIAL measuring techniques.

In this work an analysis of continuous Differential Optical Absorption Spectroscopy (DOAS) measurements of primary and secondary air pollutants (SO(2), NO(2) and O(3)) in the Athens basin is performed combined with Differential Absorption Lidar (DIAL) vertical ozone measurements obtained inside the Planetary Boundary Layer (PBL) and the lower free troposphere. The measurements took place during the period May 2005-February 2007, at the National Technical University of Athens Campus (200 m above sea level (asl.), 37.96 °N, 23.78 °E). The SO(2) and NO(2) DOAS measurements showed maximum 1-hour mean values (around 20 µg/m(3) and 74 µg/m(3), respectively) in winter and did not exceed the current European Union (EU) air quality standards (European Council Directive 2008/50/EC), in contrast to ozone, which shows its maximum (around 128 µg/m(3)) in summer and frequently exceeds the EU standard for human health protection (120 µg/m(3)). If the measurements are classified according to the two most frequent flow-patterns of the air masses in the Athens basin (northern-southern circulation), it is observed that in general the atmospheric concentrations of all measured pollutants including ozone are higher when the southern circulation occurs, in comparison to the corresponding values under the northern circulation. The vertical ozone profiles obtained by DIAL were also higher under the southern circulation. During the summer months a mean difference (between the southern-northern circulations) of the order of 15-20 µg/m(3), maximized at the 0.9-1.1 km and 1.7-1.8 km height, was observed within the PBL. It was also observed that the summer surface ozone levels remained relatively high (around 80-110 µg/m(3)) even during strong northerly winds, verifying the high levels of rural surface ozone in the surrounding area reported by previous studies.

PM10 composition during an intense Saharan dust transport event over Athens (Greece).

The influence of Saharan dust on the air quality of Southern European big cities became a priority during the last decade. The present study reports results on PM(10) monitored at an urban site at 14 m above ground level during an intense Saharan dust transport event. The elemental composition was determined by Energy Dispersive X-ray Fluorescence Spectrometry (EDXRF) for 12 elements: Si, Al, Fe, K, Ca, Mg, Ti, S, Ni, Cu, Zn and Mn. PM(10) concentrations exceeded the EU limit (50 µg/m(3)) several times during the sampling period. Simultaneous maxima have been observed for the elements of crustal origin. The concentrations of all the elements presented a common maximum, corresponding to the date where the atmosphere was heavily charged with particulate matter permanently for an interval of about 10h. Sulfur and heavy metal concentrations were also associated to local emissions. Mineral dust represented the largest fraction of PM(10) reaching 79%. Seven days back trajectories have shown that the air masses arriving over Athens, originated from Western Sahara. Scanning Electron Microscopy coupled with Energy Dispersive X-ray analysis (SEM-EDX) revealed that particle agglomerates were abundant, most of them having sizes <2 µm. Aluminosilicates were predominant in dust particles also rich in calcium which was distributed between calcite, dolomite, gypsum and Ca-Si particles. These results were consistent with the origin of the dust particles and the elemental composition results. Sulfur and heavy metals were associated to very fine particles <1 µm.

Optical properties of tropospheric aerosols determined by lidar and spectrophotometric measurements (Photochemical Activity and Solar Ultraviolet Radiation campaign).

We present the results of the aerosol measurements carried out over the Aegean Sea during the Photochemical Activity and Solar Ultraviolet Radiation campaign held in Greece during June 1996. Simultaneous observations performed with a lidar and a double-monochromator spectrophotometer allowed us to retrieve the optical depth, the Angström coefficient, and the backscatter-to-extinction ratio. The Sun photometric data can be used to improve quantitative aerosol measurements by lidar in the Planetary Boundary Layer. Systematic errors could arise otherwise, because the value of the backscatter-to-extinction ratio has to be supplied. Instead this ratio can be retrieved experimentally by use of an iterative solution of the lidar equation.

Multiwavelength lidar for ozone measurements in the troposphere and the lower stratosphere.

To study the ozone spatial and temporal evolution in the atmosphere, lidar systems have proved to be adequate but have remained complex. We define in this paper the main characteristics of a UVDIAL system for ground based and airborne ozone measurements in the troposphere and the lower stratosphere both for daytime and nighttime operation. A multiwavelength lidar system using either Rayleigh/Mie signals or the Raman nitrogen signal, is discussed as a way to efficiently correct the ozone measurements from the systematic bias due to aerosol and other interference gases (i.e. SO(2)) in the lower troposphere. Two types of lasers (solid state and excimer) are compared, as both lasers are suitable for long term field operation and airborne use.

Lymphocyte markers and clinical expression of lymphoproliferative disorders with moderate lymphocytosis.

Lymphoproliferative syndrome with well differentiated lymphocytes and moderate lymphocytosis in the peripheral blood includes a heterogeneous group of disorders, that present often difficulties in classification. We have studied the lymphocyte markers (ER, EMR, sIg and T3, T4, T8 antigens) in 36 cases who had lymphocytic infiltration in the bone marrow and peripheral lymphocyte counts less than 15 X 10(9) l-1. Four cases (11.1%) had the characteristics of T8 lymphocytosis and 31 had a B cell monoclonal proliferation in the peripheral blood. Of these, four were sIg-, EMR+, 19 were sIg+, EMR+ and 8 were sIg+, EMR-. Most patients (17/32) had the clinical picture of stage 0 and I B-CLL. Six cases presented as pure splenomegalic form of CLL, three had the features of immunocytic lymphoma and five had the features of lymphocytic lymphoma. It is concluded that the majority of lymphoproliferative disorders presenting with moderate lymphocytosis represent early forms of B-CLL. Occasionally cases of lymphocytic or immunocytic lymphoma may present problems of differential diagnosis since there may be a dissociation of phenotypic characteristics of lymphocytes between tissues and peripheral blood.

Development of chronic lymphocytic leukaemia in a patient with polycythaemia vera.

A 73-year-old patient who had polycythaemia vera (PV), and who 6 years later developed chronic lymphocytic leukaemia (CCL) is described. 2 years after the appearance of CLL, the polycythaemic phase showed a remission following treatment with phlebotomy and busulfan. CLL did not make all the characteristics of PV disappear: leucocyte alkaline phosphatase and fibrosis of the bone marrow remained increased and the erythrocyte sedimentation rate remained low. The abnormal lymphocytes were B-cells and had the peculiarity that most of their nuclei showed a deep cleft, and some were bilobed. Chromosomal studies of the bone marrow showed the presence of a metacentric chromosome in the C-group, while the karyotype of the peripheral blood was normal. This case is described because of the rarity of the coexistence of these 2 diseases in the same patient.

Effect of ionizing radiation on platelet function in vitro.

The effect of ionizing radiation on platelet function was investigated in vitro. Platelet-rich plasma (300 x 10(9/1)) was irradiated with doses of 1, 4, 10, 20 and 50 Gy. Platelet function tests were performed on both irradiated and control (non-irradiated) platelet samples. The platelet function tests were (1) platelet aggregation by ADP (1, 2, 4 mumol final concentration), adrenaline and collagen, (2) ADP-release from platelets, (3) clot retraction and (4) platelet factor-3 availability. It was found that roentgen irradiation of platelets in vitro did not affect these platelet functions tests.

Chromosome aberrations and prognosis in preleukaemia.

24 patients with preleukaemia were cytogenetically studied by the G-banding staining technique. All patients developed later frank acute non-lymphocytic leukaemia and died. 13 patients had a completely normal karyotype (NN-patients) with a median survival time of 8 months. 6 patients had both normal and abnormal metaphases (AN-patients) with a median survival time of 18.5 months, while 5 patients had abnormal metaphases only (AA-patients) with a median survival time of 3 months.

Cytogenetic studies in preleukaemia using the G-banding staining technique.

15 patients with preleukaemia were cytogenetically studied during the preleukaemic state by using the G-banding staining technique. It was found that 9 patients had a completely normal karyotype, while the other 6 showed various chromosomal abnormalities, numerical (trisomies in 5 cases) and structural (deletion in 1 case and a marker chromosome in 1 case). The abnormalities concerned group C in all 6 cases, while group A was involved in 3 cases. G-banding technique revealed that trisomy C affected the chromosomes nos 8 (2 cases) and 9 (3 cases); also a deleted chromosome 11 (11q-) was identified in 1 case and a marker chromosome in 1, the origin of which was established as a translocation between chromosomes 3 and 6. The abnormalities of group A concerned chromosome no 3. The abnormalities found in our cases, using the G-banding technique, were similar to those described in acute leukaemia.

Platelet function, blood coagulation and fibrinolysis in Behcet's syndrome.

In 10 patients with Behcet's syndrome, various parameters of platelet function, blood coagulation and fibrinolysis were studied. With varying frequency the following abnormalities were found: increased retention of platelets in glass bead column, reduced platelet aggregation to low concentrations of adenosine diphosphate, elevated plasma levels of fibrinogen concentration and factor VIII activity, increased plasma antiheparin activity and impairment of fibrinolytic activity. The above abnormalities were found long after the last thrombotic episode and were more frequent in patients with a history of thrombophlebitis. It is suggested that certain hemostatic abnormalities accompany or form part of Behcet's syndrome and that they are related to the thrombotic complications characteristic of this syndrome.

Platelet function tests during major operation for gastro-intestinal carcinoma.

Platelet function tests were performed on 15 patients undergoing major operation preoperatively, during anaesthesia and 30 minutes and 3 hours after the beginning of operation. It was found that during anaesthesia platelet retention in a glass bead column and platelet aggregation were slightly reduced. During operation the bleeding time and the delay period of the collagen-induced aggregation were progressively prolonged, and the aggregation induced by ADP at a final concentration of 1 and 2 micrometer and by adrenaline was progressively reduced.

Postoperative platelet function in patients on small subcutaneous doses of heparin.

Several platelet function tests were performed on 31 patients undergoing major operations, who recieved prophylactically small subcutaneous doses of heparin. A group of 15 similar patients without heparin served as controls. It was found that postoperatively in both groups (a) the platelet retention in glass bead column was significantly increased (p less than 0.001), (b) the platelet aggregation by ADP 1 micronM was slightly increased, (c) the collagen-induced aggregation, ADP release and the bleeding time remained unchanged and (d) the platelet counts decreased in the first 2 postoperative days and increased thereafter. There was no difference between patients on heparin and controls.

Familial thrombosis due to antithrombin III deficiency in a Greek family.

A Greek family with hereditary antithrombin III (AT III) deficiency associated with venous thrombosis is reported. 5 members of the family were affected. In these patients, AT III and heparin cofactor activities were decreased. Immunoreactive AT III showed a positive correlation to both AT III and heparin cofactor activities. alpha2-Macroglobulin and alpha1-antitrypsin were normal. The pattern of inheritance of the defect is autosomal dominant.