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Effective nanoprobes and contrast agents are urgently sought for earlystage cancer diagnosis. Upconversion nanoparticles (UCNPs) are considerable alternatives for bioimaging, cancer diagnosis, and therapy. Yb 3+ / Tm 3+ co-doping brings both emission and excitation wavelengths into the near-infrared (NIR) region, which is known as "optical transmission window" and ideally suitable for bioimaging. Here, NIR emission intensity is remarkably enhanced by 113 times with the increase of Yb 3+ concentration from 20% to 98% in polyethylene glycol (PEG) modifi ed NaYF 4 :Yb 3+ / Tm 3+ UCNPs. PEG-UCNPs-5 (98% Yb 3+ ) can act as excellent nanoprobes and contrast agents for trimodal upconversion (UC) optical/CT/T 2 -weighted magnetic resonance imaging (MRI). In addition, the enhanced detection of lung in vivo long-lasting tracking, as well as possible clearance mechanism and excretion routes of PEG-UCNPs-5 have been demonstrated. More signifi cantly, a small tumor down to 4 mm is detected in vivo via intravenous injection of these nanoprobes under both UC optical and T 2 -weighted MRI modalities. PEG-UCNPs-5 can emerge as bioprobes for multi-modal bioimaging, disease diagnosis, and therapy, especially the early-stage tumor diagnosis.

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Please check the document version of this publication:• A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. Abstract Condition-based maintenance (CBM) is becoming increasingly important due to the development of advanced sensor and information technology, which facilitates the remote collection of condition data. We propose a new CBM policy for multi-component systems with continuous stochastic deteriorations. To reduce the high setup cost of maintenance, a joint maintenance interval is introduced. With this interval and the control limits of components as decision variables, we develop a model for the minimization of the average long-run maintenance cost rate of the systems. Moreover, a numerical study of a production system consisting of a large number of non-identical components is presented, including a sensitivity analysis. Finally, our policy is compared to a failure-based policy and an age-based policy, in order to evaluate the cost-saving potential.

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